development of novel method for rapid extract of
TRANSCRIPT
The Pennsylvania State University
The Graduate School
College of Engineering
Development of Novel Method for Rapid Extract of
Radionuclides from Solution Using Polymer Ligand Film
A Dissertation in
Nuclear Engineering
by
Jung H. Rim
2013 Jung H. Rim
Submitted in Partial Fulfillment of the Requirements
for the Degree of
Doctor of Philosophy
December 2013
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The dissertation of Jung H. Rim was reviewed and approved by the following: Kenan Ünlü Professor of Nuclear Engineering, Director of Radiation Science and Engineering Center Dissertation Advisor Chair of Committee Dominic S. Peterson Deputy Group Leader, MST-7 Polymers and Coatings Los Alamos National Laboratory Special Member Jack S. Brenizer Jr. J. ‘Lee’ Everett Professor of Mechanical and Nuclear Engineering Igor Jovanovic Associate Professor of Nuclear Engineering Bashore Faculty Development Professorship
Dan Sykes Senior Lecturer and Director, Analytical Instructional Laboratories Stephen LaMont Chief Scientist, Nuclear Materials Information Program Los Alamos National Laboratory Special Member Arthur Motta Chair of Nuclear Engineering Professor of Nuclear Engineering and Materials Science and Engineering *Signatures are on file in the Graduate School
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Abstract
Accurate and fast determination of the activity of radionuclides in a sample is
critical for nuclear forensics and emergency response. Radioanalytical techniques are
well established for radionuclides measurement, however, they are slow and labor
intensive, requiring extensive radiochemical separations and purification prior to
analysis. With these limitations of current methods, there is great interest for a new
technique to rapidly process samples. This dissertation describes a new analyte extraction
medium called Polymer Ligand Film (PLF) developed to rapidly extract radionuclides.
Polymer Ligand Film is a polymer medium with ligands incorporated in its matrix that
selectively and rapidly extract analytes from a solution. The main focus of the new
technique is to shorten and simplify the procedure necessary to chemically isolate
radionuclides for determination by alpha spectrometry or beta counting.
Five different ligands were tested for plutonium extraction: bis(2-ethylhexyl)
methanediphosphonic acid (H2DEH[MDP]), di(2-ethyl hexyl) phosphoric acid (HDEHP),
trialkyl methylammonium chloride (Aliquat-336), 4,4'(5')-di-t-butylcyclohexano 18-
crown-6 (DtBuCH18C6), and 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]).
The ligands that were effective for plutonium extraction further studied for uranium
extraction. The two ligands, H2DEH[MDP] and HDEHP, which showed effectiveness in
plutonium extraction were extensively studied. The extraction of strontium was
exclusively studied with DtBuCH18C6. This particular ligand was effective for strontium
separation in resin bead form. However, in PLF form, the ligand became completely
ineffective for strontium extraction.
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The plutonium recovery by PLFs has shown dependency on nitric acid
concentration and ligand to total mass ratio. H2DEH[MDP] PLFs performed best with
1:10 and 1:20 ratio PLFs. 50.44% and 47.61% of plutonium were extracted on the surface
of PLFs with 1M nitric acid for 1:10 and 1:20 PLF, respectively. HDEHP PLF provided
the best combination of alpha spectroscopy resolution and plutonium recovery with 1:5
PLF when used with 0.1M nitric acid. The overall analyte recovery was lower than
electrodeposited samples, which typically has recovery above 80%. However, PLF is
designed to be a rapid field deployable screening technique and consistency is more
important than recovery. PLFs were also tested using blind quality control samples and
the activities were accurately measured. It is important to point out that PLFs were
consistently susceptible to analytes penetrating and depositing below the surface. The
internal radiation within the body of PLF is mostly contained and did not cause excessive
self-attenuation and peak broadening in alpha spectroscopy. The analyte penetration issue
was beneficial in the destructive analysis. The extra plutonium contained in the PLF body
gave additional signal in the analysis. Plutonium was successfully back-extracted from
PLF and procedures were established for isotopic analysis by thermal ionization mass
spectrometry (TIMS). H2DEH[MDP] PLFs showed few advantages over HDEHP PLFs.
H2DEH[MDP] PLFs showed better sample recovery consistency than HDEHP. The
sample to sample variation in plutonium recovery was comparable to variation observed
with electrodeposited samples. H2DEH[MDP] PLF was also capable of co-extracting or
selectively extracting plutonium over uranium depending on the PLF composition. With
1:5 H2DEH[MDP] PLF, about 23% of plutonium and 20% uranium were co-extracted.
v
On the other hand, both 1:10 and 1:20 PLFs were preferably extracting plutonium over
uranium at the same condition.
H2DEH[MDP] PLF was tested with environmental samples to fully understand
the capabilities and limitations of the PLF in relevant environments. The extraction
system was very effective in extracting plutonium from environmental water collected
from Mortandad Canyon at Los Alamos National Laboratory with minimal sample
processing. Soil samples were tougher to process than the water samples. Analytes were
first leached from the soil matrixes using nitric acid before processing with PLF. This
approach had a limitation in extracting plutonium using PLF. The soil samples from
Mortandad Canyon, which are about 1% iron by weight, were effectively processed with
the PLF system. Only 5.11x10-3% of iron from soil was leached using 1M nitric acid. The
Rocky Flats soils with higher iron content (2.6%) were unsuccessfully processed with
PLF for plutonium extraction. The leached solutions from the soil with higher iron
concentration had dark reddish color, which indicates a presence of large concentration of
iron. The large amount of iron in leached solution interfered and rendered PLF ineffective
for analyte extraction. No detectable activities were measured from Rocky Flats samples
processed with PLFs.
Even with certain limitations of the PLF extraction system, this technique was
able to considerably decrease the sample analysis time. The entire environmental sample
was analyzed within one to two days. The decrease in time can be attributed to the fact
that PLF is replacing column chromatography and electrodeposition with a single step for
preparing alpha spectrometry samples. The two-step process of column chromatography
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and electrodeposition takes a couple days to a week to complete depending on the
sample. The decrease in time and the simplified procedure make this technique a unique
solution for application to nuclear forensics and emergency response. A large number of
samples can be quickly analyzed and selective samples can be further analyzed with more
sensitive techniques based on the initial data. A procedure was established to perform
TIMS analysis and plutonium isotopics were measured in a number of PLF samples. The
deployment of a PLF system as a screening method will greatly reduce a total analysis
time required to gain meaningful isotopic data for the nuclear forensics application.
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TABLE OF CONTENTS
LIST OF FIGURES ..................................................................................................... x
LIST OF TABLES ....................................................................................................... xvi
ACKNOWLEDGEMENTS ......................................................................................... xviii
Chapter 1 Introduction ................................................................................................ 1
Chapter 2 Polymer Ligand Film Preparation .............................................................. 5
2.1 Introduction ..................................................................................................... 5 2.2 Background: Polymer Thin Film Deposition Techniques .............................. 5
2.2.1 Solvent Casting ..................................................................................... 5 2.2.2 Spin Coating ......................................................................................... 7 2.2.3 Spray Coating ....................................................................................... 9 2.2.4 Chemical Vapor Deposition ................................................................. 10 2.2.5 Pulsed Laser Deposition ....................................................................... 12 2.2.6 PLF Preparation Method Selection ...................................................... 13
2.3 PLF Preparation Experiment .......................................................................... 15 2.3.1 PLF Stock Solution ............................................................................... 15 2.3.2 Solvent Casting Method ....................................................................... 19 2.3.3 Nebulizer Spraying Coating Method .................................................... 22 2.3.4 Spin Coating Method ............................................................................ 24
2.4 PLF Preparation Conclusions ......................................................................... 26
Chapter 3 Bis(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP]) ................ 28
3.1 Introduction ..................................................................................................... 28 3.2 Theory and Background ................................................................................. 28 3.3 Plutonium and Uranium Extraction ................................................................ 31
3.3.1 Analyte Extraction Characterization .................................................... 32 3.3.2 Time Dependency Test ......................................................................... 42 3.3.3 Consistency Study ................................................................................ 45 3.3.4 Blind Study ........................................................................................... 49 3.3.5 Alternate PLFs ...................................................................................... 50
3.4 Digital Autoradiography ................................................................................. 52 3.5 Uranium Analysis ........................................................................................... 54 3.6 Mass Spectroscopy Analysis .......................................................................... 56
3.6.1 Back-extraction with Nitric Acid and Deionized Water ...................... 58 3.6.2 Back-extraction with Isopropanol ........................................................ 60 3.6.3 TIMS Analysis ...................................................................................... 61
3.7 H2DEH[MDP] PLF Conclusions .................................................................... 67
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Chapter 4 Di(2-ethylhexyl) phosphoric acid (HDEHP).............................................. 69
4.1 Introduction ..................................................................................................... 69 4.2 Theory and Background ................................................................................. 69 4.3 Plutonium and Uranium Extraction ................................................................ 72
4.3.1 Analyte Extraction Characterization .................................................... 73 4.3.2 Analyte Extraction Time Dependency ................................................. 80 4.3.3 Consistency Study ................................................................................ 82 4.3.4 Alternate PLFs ...................................................................................... 89
4.4 Surface Characterization ................................................................................. 90 4.5 Uranium Analysis ........................................................................................... 93 4.6 Mass Spectroscopy Analysis .......................................................................... 94
4.6.1 Back-extraction with Nitric Acid and Deionized Water ...................... 95 4.6.2 Back-extraction with Isopropanol ........................................................ 96 4.6.3 TIMS Analysis ...................................................................................... 97
4.7 HDEHP PLF Analysis Conclusions ............................................................... 99
Chapter 5 Other Ligands ............................................................................................. 101
5.1 Trialkyl methylammonium chloride (Aliquat-336) ........................................ 101 5.1.1 PLF Preparation and Testing ................................................................ 103
5.2 4,4’,(5’)-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) ................. 104 5.2.1 Plutonium Extraction ............................................................................ 106 5.2.2 Strontium Extraction ............................................................................ 109
5.3 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]) ............................... 111 5.3.1 Plutonium Extraction ............................................................................ 114
Chapter 6 Environmental Sample Analysis ................................................................ 118
6.1 Soil Sample Analysis ...................................................................................... 119 6.1.1 Soil Characterization ............................................................................ 119 6.1.2 Mortandad Canyon Soil Leaching Study ............................................. 122 6.1.3 Rock Flats Soil Leaching Study ........................................................... 127
6.2 Water Sample Analysis................................................................................... 132 6.2.1 Environmental Water Characterization ................................................ 132 6.2.2 Environmental Water Processing with PLF ......................................... 133
6.3 Environmental Sample Analysis Conclusions ................................................ 135
Chapter 7 Summary and Conclusions ......................................................................... 137
7.1 Recommendations and Future Studies............................................................ 140
Appendix A Counting Software Code ........................................................................ 142
Appendix B H2DEH[MDP] PLF Plutonium Distribution Maps................................. 146
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Appendix C HDEHP PLF Plutonium Distribution Maps ........................................... 149
Appendix D Gamma Spectra from Mortandad Canyon Soil Samples ....................... 152
Bibliography ................................................................................................................ 154
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LIST OF FIGURES
Figure 1-1 Diagram comparing conventional sample preparation method and PLF method .................................................................................................................. 4
Figure 2-1 (A) Stationary solvent casting operation, (B) Continuous solvent casting using a belt system ................................................................................... 6
Figure 2-2 A graphical depiction of four stages in spin coating .................................. 7
Figure 2-3 Chemical vapor deposition setup .............................................................. 11
Figure 2-4 Pulsed laser deposition setup ..................................................................... 12
Figure 2-5 PLF stock solution (A) with un-dissolved polystyrene, (B) with polystyrene completely dissolved ......................................................................... 18
Figure 2-6 PLFs prepared with solvent casting method .............................................. 20
Figure 2-7 Crown ether PLFs with large population of bubbles along the edge ......... 20
Figure 2-8 A Latex and Nitrile substrates damaged by THF ....................................... 22
Figure 2-9 Nebulizer setup for PLF spraying .............................................................. 22
Figure 2-10 Nebulizer spray coating setup .................................................................. 23
Figure 2-11 Sprayed PLF (A) before heat treatment (B) after heat treatment ............. 24
Figure 2-12 Uneven polymer film coating on stainless steel substrates by spin coating method ...................................................................................................... 25
Figure 2-13 PLF spin coating setup ............................................................................. 25
Figure 3-1 Chemical structure of H2DEH[MDP] ........................................................ 29
Figure 3-2 Alkaline earth metal extraction mechanism with H2DEH[MDP] .............. 30
Figure 3-3 H2DEH[MDP] distribution ratio dependency on HCl concentration for various ions ........................................................................................................... 31
Figure 3-4 Alpha spectroscopy sample tray (A) before modification (B) after modification .......................................................................................................... 33
Figure 3-5 The baseline performance of H2DEH[MDP] PLF in plutonium extraction as a function of nitric acid concentration ............................................. 34
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Figure 3-6 Plutonium recovery by 1:10 through 1:20 H2DEH[MDP] PLF as a function of nitric acid concentration ..................................................................... 35
Figure 3-7 1:25 H2DEH[MDP] PLF with damaged surface ....................................... 36
Figure 3-8 Unaccounted plutonium by H2DEH[MDP] PLF as function of nitric acid concentration ................................................................................................. 37
Figure 3-9 Unaccounted plutonium activity with 8M nitric acid ................................ 38
Figure 3-10 Plutonium penetration mechanism experiment by varying tracer solution volumes ................................................................................................... 39
Figure 3-11 Schematic diagram of PLF analyte extraction mechanism ...................... 40
Figure 3-12 H2DEH[MDP] PLF plutonium recovery at different exposure time ....... 43
Figure 3-13 H2DEH[MDP] PLFs from two batches ................................................... 47
Figure 3-14 Plutonium recoveries by two different batch 1:20 H2DEH[MDP] PLFs with 0.1M nitric acid solution ..................................................................... 47
Figure 3-15 Digital autoradiography image from 1:20 H2DEH[MDP] PLF ............. 53
Figure 3-16 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image .............................................................................. 54
Figure 3-17 Uranium recovery by H2DEH[MDP] PLF as function of nitric acid concentration ......................................................................................................... 55
Figure 3-18 H2DEH[MDP] PLF Pu and U extraction efficiency with 1M nitric acid ........................................................................................................................ 56
Figure 3-19 (A) TIMS turret with triple-filament (B) TIMS sample turret in chamber ................................................................................................................. 62
Figure 3-20 Comparison of TIMS 240/239Pu isotopic ratio measurements from back-extracted samples and known values ........................................................... 63
Figure 3-21 Illustration of PLF direct sample mounting on TIMS filament ............... 64
Figure 3-22 TIMS filament prepared with (A) ligand-polymer method (B) ligand complex method .................................................................................................... 65
Figure 3-23 TIMS spectrum from 242Pu sample prepared by ligand-polymer method .................................................................................................................. 66
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Figure 4-1 Chemical structure of HDEHP ................................................................... 69
Figure 4-2 HDEHP distribution ratio dependency on HNO3 concentration for various ions [50] ................................................................................................... 72
Figure 4-3 HDEHP ligand based PLFs ........................................................................ 73
Figure 4-4 The baseline performance of HDEHP PLF in plutonium extraction as a function of nitric acid concentration ..................................................................... 74
Figure 4-5 Alpha spectra for 1:2 (blue) and 1:5 (red) PLFs ........................................ 76
Figure 4-6 Plutonium recovery by 1:6 through 1:20 HDEHP PLF as a function of nitric acid concentration ....................................................................................... 78
Figure 4-7 Plutonium recovery by 1:2 through 1:5 HDEHP PLF as a function of nitric acid concentration ....................................................................................... 78
Figure 4-8 Plutonium recovery by HDEHP PLF as function of PLF composition ..... 79
Figure 4-9 Unaccounted plutonium by H2DEH[MDP] PLF as function of nitric acid concentration ................................................................................................. 80
Figure 4-10 HDEHP and H2DEH[MDP] PLF plutonium recoveries at different exposure time ........................................................................................................ 81
Figure 4-11 Plutonium recoveries by 1:5 HDEHP PLFs with 0.1M nitric acid solution ................................................................................................................. 84
Figure 4-12 Comparison of two HDEHP PLF batches after alpha counting ............... 85
Figure 4-13 1:5 HDEHP PLF (A) after heat treatment (B) after 16 day outgassing ... 86
Figure 4-14 Alpha spectra comparison between heat treated HDEHP PLF (blue) and air dried PLF (red) ......................................................................................... 87
Figure 4-15 1:5 HDEHP PLF surface color progression over 12 days ....................... 88
Figure 4-16 Heat treated 1:5 HDEHP PLF surface color progression over 12 days ... 89
Figure 4-17 Alpha spectra comparison between for heat treated 1:5 HDEHP and regular PLFs .......................................................................................................... 90
Figure 4-18 SEM images for different ratio HDEHP PLFs ......................................... 91
Figure 4-19 Digital autoradiography image of 1:2 and 1:5 HDEHP PLFs.................. 92
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Figure 4-20 Plutonium distribution map of HDEHP PLF generated from digital autoradiography image ......................................................................................... 93
Figure 4-21 Uranium recovery by HDEHP PLF as function of nitric acid concentration ......................................................................................................... 94
Figure 4-22 Comparison of TIMS 239/240Pu isotopic ratio measurements from back-extracted samples and known values ........................................................... 98
Figure 5-1 Chemical structure of Aliquat-336 ............................................................. 101
Figure 5-2 Aliquot-336 distribution ratio dependency on HNO3 concentration for various ions ........................................................................................................... 102
Figure 5-3 Aliquat-336 PLF damaged by high concentration nitric acid .................... 104
Figure 5-4 Strontium 18-crown-6 complex ................................................................. 105
Figure 5-5 Chemical structure of (A) DC18C6 (B) DtBuCH18C6 ............................. 105
Figure 5-6 DtBuCH18C6 distribution ratio dependency on HNO3 concentration for various ions ..................................................................................................... 106
Figure 5-7 Crown ether PLFs prepared with solvent casting method ......................... 107
Figure 5-8 Plutonium recovery by crown ether PLF as a function of nitric acid concentration ......................................................................................................... 108
Figure 5-9 Unaccounted plutonium recovery by crown ether as a function of nitric acid concentration ................................................................................................. 108
Figure 5-10 Crown ether PLFs damaged by high concentrated nitric acid ................. 109
Figure 5-11 Crown ether PLF coated LSC vial diagram ............................................. 110
Figure 5-12 Chemical structure of HEH[EHP] ............................................................ 112
Figure 5-13 HEH[EHP] distribution ratio dependency on HNO3 concentration for various ions ........................................................................................................... 113
Figure 5-14 HEH[EHP] distribution ratio relative to HDEHP [79] ............................ 114
Figure 5-15 Plutonium recovery by HEH[EHP] PLF as a function of nitric acid concentration ......................................................................................................... 115
Figure 5-16 Unaccounted plutonium recovery by HEH[EHP] as a function of nitric acid concentration ....................................................................................... 116
xiv
Figure 6-1 Mortandad Canyon soil samples ................................................................ 119
Figure 6-2 Fusion sample (A) before (B) after processing with the muffle furnace ... 122
Figure 6-3 Leached solution (A) before (B) after syringe filtering ............................. 123
Figure 6-4 Plutonium leaching dependency on the nitric acid concentration .............. 125
Figure 6-5 Plutonium leaching dependency on time for 1M ntiric acid and white distilled vinegar .................................................................................................... 126
Figure 6-6 239+240Pu extracted with 1:20 H2DEH[MDP] PLF at different leaching and exposure time ................................................................................................. 127
Figure 6-7 Rocky Flats soil leaching with vinegar or various concentration nitric acid solutions ........................................................................................................ 129
Figure 6-8 Rocky Flats soil leached solutions after syringe filtering .......................... 129
Figure 6-9 Residue left on beaker after leached nitric acid was dried ......................... 131
Figure 6-10 Rocky Flats leached solution stippled on 1:20 H2DEH[MDP] PLFs ...... 131
Figure B-1 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2A) ......................................... 146
Figure B-2 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2B) ......................................... 146
Figure B-3 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2C) ......................................... 147
Figure B-4 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2D) ......................................... 147
Figure B-5 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2G) ......................................... 147
Figure B-6 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2H) ......................................... 148
Figure B-7 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2I) .......................................... 148
Figure B-8 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2J) .......................................... 148
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Figure C-1 Plutonium distribution map of 1:2 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2A) .................................................... 149
Figure C-2 Plutonium distribution map of 1:2 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2B) .................................................... 149
Figure C-3 Plutonium distribution map of 1:2 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2C) .................................................... 150
Figure C-4 Plutonium distribution map of 1:5 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2D) .................................................... 150
Figure C-5 Plutonium distribution map of 1:5 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2E) .................................................... 150
Figure C-6 Plutonium distribution map of 1:5 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2F) ..................................................... 151
Figure D-1 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2A) .............................................................................................................. 152
Figure D-2 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2B) .............................................................................................................. 153
Figure D-3 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2C) .............................................................................................................. 153
Figure D-4 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2D) .............................................................................................................. 153
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LIST OF TABLES
Table 2-1 Advantages and disadvantages of each thin film technique ........................ 14
Table 2-2 Commonly used solvents to dissolve polymers ........................................... 17
Table 2-3 Polystyrene and Tetrahydrofuran properties ............................................... 18
Table 3-1 Plutonium penetration dependency on solution volume ............................. 40
Table 3-2 Average FWHM and Tailing for H2DEH[MDP] PLFs tested for plutonium extraction ............................................................................................. 42
Table 3-3 Plutonium activities per 100 fg of analyte ................................................... 45
Table 3-4 Mass of components used to prepare two H2DEH[MDP] PLF batches for the consistency study ...................................................................................... 46
Table 3-5 Average plutonium recovery by each batch ................................................ 48
Table 3-6 Plutonium activity measurements from blind samples using 1:20 H2DEH[MDP] PLF .............................................................................................. 49
Table 3-7 Uranium tracer activity information ............................................................ 55
Table 3-8 Plutonium back-extraction with nitric acid and DI water ........................... 59
Table 3-9 Plutonium back-extracted from H2DEH[MDP] PLF using isopropanol ..... 61
Table 3-10 240/239Pu isotopic ratio for each samples .................................................... 62
Table 3-11 Information of plutonium standards used in TIMS analysis ..................... 66
Table 4-1 Alpha spectra resolutions and tailing terms for HDEHP PLFs ................... 75
Table 4-2 Mass of components used to prepare two HDEHP PLF batches for consistency study .................................................................................................. 83
Table 4-3 Average plutonium recovery by HDEHP PLF batches ............................... 84
Table 4-4 Plutonium recovery improvement after outgassing and heat treatment ...... 86
Table 4-5 HDEHP PLF plutonium back-extraction with nitric acid and DI water ..... 95
Table 4-6 HDEHP PLF plutonium back-extraction with isopropanol......................... 97
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Table 6-1 Mortandad Canyon soil radionuclide activities measured with HPGe ........ 120
Table 6-2 Elemental information gained from NAA ................................................... 121
Table 6-3 Elements leached from Mortandad Canyon soil using nitric acid ............... 124
Table 6-4 Rocky Flats standard soil certified radionuclide activities .......................... 128
Table 6-5 239+240Pu leached activities from Rock Flats soil and percent activity recoveries based on certified values ..................................................................... 130
Table 6-6 Elemental composition of Rocky Flats SRM .............................................. 132
Table 6-7 Simulated environmental water sample plutonium recoveries .................... 134
xviii
ACKNOWLEDGEMENTS
I would like to thank my Dissertation Advisor, Dr. Kenan Ünlü, for his advice and
the support for this research. His guidance was instrumental in completion of this study. I
would like to also sincerely appreciate my laboratory mentor, Dr. Dominic Peterson, for
providing me with an opportunity to conduct research at the Los Alamos National
Laboratory. It was truly a valuable experience that I have had and will never forget all the
expert guidance that was given to me. In addition, I would not have been able to complete
my work without the help from the Claudine Armenta and Edward Gonzales. Dr. Stephen
LaMont was also essential in completing this study. I also would like to show my
gratitude to staffs at the Penn State Radiation Science & Engineering Center for their
support. Finally, I would like to thank my family, Miel and Aleena, for all their patience
and support.
This research was performed under the Nuclear Forensics Graduate Fellowship
Program which is sponsored by the U.S. Department of Homeland Security’s Domestic
Nuclear Detection Office and the U.S. Department of Defense’s Defense Threat
Reduction Agency. Los Alamos National Laboratory is operated by Los Alamos National
Security, LLC for the U.S. Department of Energy under contract number DE-AC52-
06NA25396. This document had been reviewed and assigned publication number: LA-
UR-13-26848 Version 3.
1
1. Chapter 1
Introduction
The goal of this research was to develop a novel method to selectively extract
uranium, plutonium, and strontium from a solution using Polymer Ligand Films (PLF) to
assist with generating rapid data during nuclear forensics investigations. This new
radioanalytical technique showed a great potential to be deployed during a nuclear
emergency as a way to deliver fast and reliable nuclear forensics or consequence
management data. High sample throughput is critical in an emergency response since
there is a potential need to analyze an enormous number of samples in a short time.
Current radioanalytical techniques are quite mature and well established for the analysis
of many radionuclides of interest. However, these are not well suited for rapid analysis or
pre-screening of samples to determine which might be the best suited for performing a
more accurate but time consuming set of analyses. Also, these classical methods require a
fully functional chemistry laboratory to process the samples, which greatly limits the
possibility of field analysis. These limitations of classical procedures greatly hinder the
ability to accurately assess and respond to an incident in a prompt manner.
A PLF is a thin polymer medium with ligands incorporated on to its structure to
enable selective extraction of analytes from a solution. PLFs developed in this research
were designed to use as a fast screening method for radionuclide measurement. The main
focus will be to shorten and simplify the procedure for chemically processing samples
and preparing them for radiometric counting. To achieve this goal, PLFs were
2
synthesized to separate anlaytes directly from solution onto a surface suitable for
radiometric counting techniques, such as alpha, beta, and gamma spectroscopy.
Several authors have reported the possibility of extracting both radioactive and
non-radioactive analytes using thin film substrates [1]–[7]. The thin film extraction
technique is similar to a resin based extraction with an added benefit of easier path
forward for radiometric analysis. Koulouridakis et al. were successful in selectively
extracting mercury from a large volume solution using a membrane with 24 hours of
equilibration time. The active components of the membrane were poly(vinylchloride),
dibutyl phthalate plasticizer, tetrahydrofuran, and DTBNBA [1]. Surbeck has reported the
possibility of using 400 mm2 MnO2 thin film to effectively extract radium from a water
sample with six-hour exposure time [2]. MnO2 films were directly counted with alpha
spectroscopy and showed similar energy resolution as electrodeposited sources. Surbeck
also has used commercially available resin beads to prepare thin films for uranium
extraction. The films were prepared from finely ground resin beads, and the fine powder
was fixed onto a flat surface. Fifty percent of uranium was recovered within 4 hours, and
80% was extracted in about 20 hours [2]. The alpha spectroscopy peak resolution was not
as good as the electrodeposited samples; probably due to the unevenness of the film
surface. Wang et al. used a 54 mm2 Aliquat-366/PVC liquid membrane system to extract
Cd(II) from HCl solution [7]. The membrane was prepared by dissolving Aliquat-366 and
PVC in THF then poured into a mold. Gonzales et al. have used Bis(2-ethylhexyl)
methanediphosphonic acid based thin film for plutonium and americium separation from
the solution with a 2 hour collection time [4]. The thin film was synthesized by dissolving
ligand and poly(styrene) in THF. Gonzales et al. have also applied their technique to
3
environmental samples. Extraction efficiency and alpha spectrum resolution showed
dependency on the solution and surface chemistry [3], [4].
All reviewed literature demonstrated the effectiveness of utilizing thin films for
extraction of analytes in a solution. These studies have shown that extraction efficiencies
are greatly influenced by ligands used in the film. Also, the alpha spectroscopy resolution
is dependent on surface structure. The most important characteristic to consider a ligand
is its ability to extract analytes from the solution. The second characteristic to consider is
how strongly the ligand forms a complex with analytes. It is important to have a stable
complex to ensure that radionuclides are not discharged during extensive non-destructive
analysis.
Polymer Ligand Film is a thin polymer medium with ligands incorporated onto its
structure to enable selective extraction of analytes from a solution. PLFs developed in
this research were designed to facilitate the fast isolation of radionuclides from solutions
for screening samples. The main focus was to shorten and simplify the procedure for
separating radionuclides from solutions onto a surface appropriate for radiometric
counting. To achieve this goal, PLFs were synthesized to perform direct sorption of
analytes onto its surface for direct counting using radiometric techniques, such as alpha
and beta spectroscopy. A diagram comparing the classical method and PLF technique is
shown in Figure 1-1. The new technique combined column chromatography and
electrodeposition into a single step for alpha ray emitting samples.
4
Figure 1-1 Diagram comparing conventional sample preparation method and PLF method
PLFs were examined for plutonium, uranium, and strontium extraction. Plutonium
and uranium have always been the most important elements in nuclear forensics and
incident response due to their potential use in nuclear weapons. Isotopic ratio data for
these elements provides crucial information for identifying the origin and the intended
use of the material. The two most important uranium isotopes are 235U and 238U, which
can be determined with alpha spectroscopy. Plutonium is a man-made element with at
least 15 different radioactive isotopes. Alpha decay is the most common form of decay
for plutonium isotopes. The 240Pu/239Pu isotopic ratio provides the most important
forensic information. The origin and intended use of the material can be gathered from
the plutonium isotopic ratio. However, unlike uranium, the conventional alpha
spectroscopy is not capable of making this isotopic measurement due to similar energy of
alpha particles emitted by 239Pu and 240Pu. Mass spectrometry is the only reliable
measurement technique capable of accurately measuring the 240Pu/239Pu isotope ratio.
PLF was designed mainly for radiometry techniques but plutonium can be extracted out
of the PLF for further analysis including mass spectrometry to determine the 240Pu/239Pu
ratio.
5
2. Chapter 2
Polymer Ligand Film Preparation
2.1 Introduction
Several thin film preparation methods were investigated for Polymer Ligand Film
(PLF) preparation. Each technique was evaluated for practicality and consistency in
synthesizing PLF. Three techniques were selected and used to prepare PLFs. All three
methods used a solvent to dissolve ligand and polystyrene into a solution. Each of three
components, ligand, polystyrene, and solvent, has unique role and is equally important in
generating the PLF. Each component was carefully evaluated to select best combination
of materials.
2.2 Background: Polymer Thin Film Deposition Techniques
Polymer thin films can be prepared with several different deposition techniques.
Each of these techniques provides certain advantages and disadvantages. In this section,
these techniques are reviewed and compared for polymer thin film preparation.
2.2.1 Solvent Casting
Solvent casting is the oldest technology used to manufacture plastic films. This
technique is extremely simple to implement and produce uniform thickness film with a
maximum optical purity [8]. The polymer must be dissolved in a solvent before being
6
used in this process. Dissolving a polymer in a solvent is a slow process. At first, solvent
molecules slowly diffuse into the polymer to produce a swollen gel. If polymer-solvent
interaction is stronger than the polymer-polymer intermolecular force, then the gel slowly
dissolves into the solvent [9], [10]. Once the polymer is completely dissolved in a
solvent, the solution is transferred into a cast to form a film. The polymer film is formed
once the solvent is completely evaporated. The film is then removed from the cast. The
commercial solvent casting is a continuous process, where moving belt is utilized to
continuously generate a film. This technique is used in the industrial production of
engineering plastics, films, and sheet forming for electronic applications [8]. Stationary
and continuous solvent casting process is shown in Figure 2-1.
Figure 2-1 (A) Stationary solvent casting operation, (B) Continuous solvent casting using a belt system
Solvent casting may affect the physical and mechanical properties of the polymer
[11]. The casting process also may affect the orientation of the polymeric chains. Solvent
7
evaporation from a polymer film results in one-dimensional thickness reduction. The
orientation of the polymeric chains is determined by stretching the polymer in the planar
directions during the solvent evaporation process [11].
2.2.2 Spin Coating
Spin coating technique is widely utilized to produce thin and uniform films on the
flat substrates [12], [13]. It is a mature and cost effective technique that has been studied
extensively [14]. It has been reported that thin film thickness of 1-2 µm is routinely
prepared with this technique [13]. The technique uses centrifugal forces to spread
solution to thinly cover the entire substrate. There are four distinct stages in this process:
deposition, spin-up, spin-off, and finally evaporation [12]. Each step is illustrated
graphically in Figure 2-2.
Figure 2-2 A graphical depiction of four stages in spin coating
In the deposition step, the polymer solution is transferred to the flat substrate. The
solution can cover the entire surface or just deposited on the center of the surface. In the
spin-up step, the substrate is accelerated rapidly to a high angular velocity to radially
spread the polymer solution over the entire surface. Once the solution is spread over the
entire surface, excess mass is removed in the spin-off process. The process is similar to
the spin-up. It uses a high angular velocity to remove solution and leaves only thin
8
polymer coating on a substrate. The last step in the spin coating method is evaporation. In
this step, solvent that may still be within the film evaporates. The thickness of the film
can slightly change based on the amount of solvent evaporated in this process [15].
The thickness of the film is mainly determined by the rotation speed, solvent
viscosity, and solvent volatility [12], [13], [15]. Generally a higher rotation speed
produces thinner polymer films. The greater the solution viscosity the slower the solution
spreads over the substrate. The total spin time and speed required to achieve the thickness
increases with the increase in viscosity. Equation 2.1 shows the relation of the film
thickness to viscosity and spin speed [16],
𝑡 ∝ �𝜇𝜔
Equation 2.1
where µ is viscosity and ω is spin speed. The viscosity of the polymer solution changes
during the spin-up and spin-off processes due to the evaporation of the solvent. Rapid
acceleration may be needed for the volatile solution to achieve the desired film thickness
[16]. One of the advantages of this technique is that once the film becomes completely
uniform during the coating process, it will remain for the duration of the process [14].
The two main disadvantages of spin coating are low efficiency and limitation on
substrate size. Typical spin coating only retains 2-5% of solution dispensed onto the
substrate [14]. The rest of the solution is spun off from the substrate during the coating
process. Also, the spin coating is not ideal for the large substrates. Large substrates need
to be spun at higher angular velocity than the smaller substrates to prepare thin films [14].
9
At certain substrate size, the cost of the spin coater that can provide the required angular
speed start to become too costly.
2.2.3 Spray Coating
Polymer spray coating is a technique used to prepare thin coating on a substrate.
This technique can produce thin coating layer on irregular shaped objects at a very fast
rate [17]. Spray coating may involve liquids, gases, or solids depending on the polymer
used and the type of spray system used. The polymer can be dissolved in a suitable
solvent and this polymer solvent mixture can be used to produce a thin film using a spray
coating method. In liquid polymer system, the fluid is atomized into small droplets and
sprayed over the substrate [17], [18]. The polymer solution is forced through an orifice
and as it exits the opening, high pressure gas is used to atomize the solution [17]. A
device such as a nebulizer is routinely used for atomization purpose. The size of the
droplet exiting the orifice can be adjusted by changing solution viscosity, pressure, and
orifice size [17].
For the solid polymer, a thermal polymer spraying technique is used. As the name
implies, in thermal spraying, the polymer is melted with heat to a molten state or semi-
molten state. [18], [19]. The molten polymer is then blown through a flame shrouded
orifice by running compressed gas through the orifice [18]. The molten polymer particles
coalesce and flow to form a homogeneous coating on a substrate as it cools and dries
[19].
10
Spray coating has several drawbacks. It is difficult to have precise control over
the coating area. The stream of polymer leaving the orifice may not cover the entire
substrate and multiple coatings have to be applied to cover the entire surface. During the
spraying operation, some area may be sprayed multiple times and leave an un-even
thickness. Another issue is the large amount of volatile organic compound emitted when
using solvent to dissolve the polymer. [17]
2.2.4 Chemical Vapor Deposition
Chemical vapor deposition (CVD) is a widely used technique to produce thin
coating on substrates [20]–[22]. The technique offers highly pure and extremely uniform
films even at large specimen [20]. It was first developed to prepare inorganic films but
the majority elements have been successfully processed with CVD [20]. In a typical
CVD, volatile precursors are introduced into a reactor and react with substrate that is
heated to 1000 oC. The reaction occurs on and near the substrate and produces a desired
thin film [20], [23], [24]. The conventional CVD process works well with inorganics,
which typically do not degrades under high temperature. However, this high temperature
is undesired for the polymer thin film process. The polymer function groups are damaged
due to the temperature and lead to unwanted crosslinking [24]. Unreacted precursors and
chemical by-products are evacuated through the exhaust in the reactor. The general CVD
setup is shown in Figure 2-3.
11
Figure 2-3 Chemical vapor deposition setup
The limitation of conventional CVD is overcome by modifications to the reactants
and reactor designs [24]. In polymer CVD, vapor phase monomers are reacted to form a
pure polymer film on a substrate. One of the advantages of polymer CVD is that it can
prepare wide variety of polymers that are not typically possible with other methods. CVD
can prepare highly crosslinked insoluble polymers, conductive polymers, and copolymers
of incompatible monomers [24]. Also, the process is solventless and can be coated on
virtually any surface [23], [24]. The disadvantages of CVD are mostly related to safety
and chemical hazards. Precursors are generally toxic, corrosive, flammable, and/or
explosive [25]. Extra care must be taken to operate the system due to the precursor
toxicity.
12
2.2.5 Pulsed Laser Deposition
Pulsed laser deposition (PLD) is a widely used technique to prepare inorganic thin
films. It is also possible to prepare certain polymer thin films without any modification
and a large range of polymer films can be prepare with slight modification to the
deposition system. A typical PLD system uses a high-power UV pulsed laser, such as
krypton fluoride excimer laser, to ablate material from surface. Once material is freed
from the target surface, it is collected on a heated sample substrate to form a thin film
[26], [27]. The photon energy emitted from the UV laser is high enough to break polymer
chains and change chemical and physical properties of the polymer material [28]. This
phenomenon can be used with certain polymers, such as PTFE, to prepare thin film [29],
[30]. Polymer is ablated in monomer form then subsequently re-polymerized on sample
substrate [31].
Figure 2-4 Pulsed laser deposition setup
The PLD technique can be modified by replacing UV laser with IR pulse laser to be more
favorable for polymer film preparation. With an IR laser, chemical structure of polymer
13
is maintained during the ablation step and final product has the same property as the bulk
target material.
There are a few advantages of PLD over other techniques. It requires relatively
simple setup to prepare samples; a typical PLD setup is shown in Figure 2-4. The target
materials can be in many different solid forms, such as a powder, sintered pellets, and
single crystal [32], [33]. This technique is certainly not without limitations. The pulse
laser produces microscopic particles during the ablation process causing uneven
deposition [32], [34]. Further, the deposition area is limited to a few cm2 [34].
2.2.6 PLF Preparation Method Selection
The five methods discussed in the previous sections were carefully evaluated for
the PLF synthesis and the most suitable methods were selected. Each technique requires
vastly different sample preparation apparatus and procedures. The main advantages and
disadvantages of each polymer thin film technique are given in Table 2-1. The technique
must be easy to implement and result in minimal variation between sample to sample.
Table is generated to list pros and cons of each technique. A large number of samples
were needed to effectively test PLF for analyte extraction in varying conditions. It is
important that the PLF preparing method is cost effective and easy to scale up to provide
adequate supply of PLFs. Five methods can be categorized into two groups, solvent based
or solventless techniques.
14
Table 2-1 Advantages and disadvantages of each thin film technique Technique Pros Cons Solvent casting Simple setup
Easy to scale up Use of volatile solvent Thick deposition
Spray coating Thin coating Odd size and shape
Use of volatile solvent Uneven deposition
Spin coating High purity Use of volatile solvent Limitation on deposition size
Chemical vapor deposition
Solventless Uniform deposition
Complex setup High cost equipment Safety issue Need highly pure compounds
Pulsed laser deposition
Solventless Target materials
High cost equipment Uneven deposition Limitation on deposition size
Solvent casting, spray coating, and spin coating are all solvent based techniques.
Solvent based techniques generally have limited choices of materials that can be used as a
backing plate due to use of volatile solvent. Solvent casting is the simplest technique to
implement for PLF preparation. It is also the best method to generate large number of
PLF required for the testing. Spray and spin coating methods are both capable of
producing thinner film but these need more complicated setups than solvent casting. With
spray coating, solvent evaporates instantaneously and does not damage substrates, which
allows this technique to be possibly used with multiple substrates that are normally
impossible with other techniques.
Chemical vapor deposition and pulsed laser deposition are both solventless
techniques. These techniques are capable of producing thin films. However, both
methods are more complicated and require complex setup than the three solvent based
techniques discussed in this section. These two methods are not ideal for PLF preparation
due to the complexity and cost of apparatus.
15
Solvent casting, spray coating, and spin coating were selected for PLF
preparation. These are cost effective and simple to apply for PLF preparation. Also these
methods are easy to scale up. In the next section, each of PLF preparation methods are
carefully examined and discussed in detail.
2.3 PLF Preparation Experiment
Polymer Thin Films were prepared with three different methods: solvent casting,
spin coating, and spray coating. These three methods were easy to implement and provide
consistency in producing PLFs. All three methods used a stock solution prepared with
ligand, polystyrene, and tetrahydrofuran. The detailed discussion on the stock solution is
given in following section. The stock solution was only slightly modified for the spray
coating method to help the solution to easily flow through the nebulizer.
2.3.1 PLF Stock Solution
The stock solution was the starting point in preparing Polymer Ligand Film (PLF).
The stock solution is prepared by mixing three components: ligand, polymer, and solvent.
Each component has its unique role and is equally important in generating the PLF for
analyte extraction. The role of each component will be reviewed in this section.
The ligands are the only component within PLF that show any affinity to
radionuclides and provide active sites for the analytes extraction. It is important to select
ligands that have a strong affinity to the analyte of interest to maximize extraction by
16
forming a strong bond. The amount of ligand present in the PLF also plays a critical role
in the extraction efficiency. Several ligands are commercially available for radionuclide
extraction.
The polymer component in PLF plays a critical role in determining the film
structure stability. The structure stability of the film is important since PLF medium is
directly exposed to various concentration of nitric acid during analyte extraction process.
PLF must withstand nitric acid exposure. The thin film also must maintain its structure
rigidity during analysis. The film medium is investigated with various analytic techniques
to characterize and examine performance of each PLF. Some of these analytic techniques
are performed in special condition. Alpha spectroscopy, for example, is operated under
high vacuum conditions and requires a rigid polymer structure to prevent sample
degradation during the analysis. Electron microscopy, which is used to examine the
surface of PLF, also operates in extremely high vacuum condition. The polymer support
also influences overall resolution obtained using radiometry systems. It is essential to
have a smooth surface to achieve optimal alpha spectral resolution. The rough surface
greatly degrades the resolution of the spectrum due to source self-attenuation.
The solvent is the component that dissolves both ligand and polymer into a
solution. Ligands normally dissolve in an organic solvent very easily, but the polymer, on
the other hand, is generally harder to dissolve. Solvents that are commonly used to
dissolve polymers are listed in Table 2-2.
17
Table 2-2 Commonly used solvents to dissolve polymers Polymer Solvent Polystyrene Toluene, Benzene, Chloroform,
o-dichlorobenzene Poly(ethylene oxide) Toluene, distilled water Poly(vinyl alcohol) Distilled water Poly(vinyl chloride) N, N-dimethylacetamide (DMA), cyclohexanone,
acetone/carbon disulfide Poly(vinylidene fluoride) Tetrahydrofuran Poly(ethylen terephthalate) Tetrachloroethylene, hexan Polycarbonate Chloroform, dichloromethane Polyethylene 1,2,4-trichlorobenzene, decalin, di-namyl
ether, halogenated hydrocarbons, higher aliphatic esters and ketones, hydrocarbons, xylene (Above 80 oC for high density and 20-30 oC lower for lower density polyethylene)
Nylon 11 Trifluoroacetic acid (TFA) Polysulfone Chlorobenzene
Five different ligands were used in this study: bis(2-ethylhexyl)
methanediphosphonic acid, di(2-ethyl hexyl) phosphoric acid, trialkyl methylammonium
chloride, 4,4'(5')-di-t-butylcyclohexano 18-crown-6, and 2-ethylhexyl 2-
ethylhexylphosphonic acid. Polystyrene was exclusively used as a polymer support in this
research due to the rigidity it provides to the PLF and the good alpha spectra resolution
achieved with PLF synthesized with it. The ligands and polystyrene were dissolved with
tetrahydrofuran (THF). Physical properties of polystyrene and THF are listed in Table
2-3. THF is one of the most effective polar ethers in dissolving polystyrene bead and
ligands. THF is not commonly used for polystyrene, but it is moderately toxic compared
to other solvents. Commonly used solvents are toluene, benzene, chloroform, and o-
dichlorobenzene. The danger associated with THF is its tendency to form peroxide when
exposed to air [35]. The explosive danger can be easily mitigated by using an inhibitor
and completely sealing off the solvent from oxygen.
18
The pictures of stock solution are shown in Figure 2-5. It normally takes about
two days to completely dissolve polystyrene beads and only a short time to dissolve
ligands in THF. The stock solutions were mixed with a vortex mixer before each use to
ensure even distribution of ligands and polystyrene. It is important to have a stock
solution with an even distribution of ligands and polymer to limit variability in PLFs
from the same batch solution.
Table 2-3 Polystyrene and Tetrahydrofuran properties Polystyrene Tetrahydrofuran Molecular Formula [CH2CH(C6H5)]n C4H8O Density (g/mL) 1.05 0.889 Boiling Point (ºC) N/A 65-67 Melting Point (ºC) 240 -108 Flash Point (ºC) N/A -17.2
Ligands used in this experiment were purchased from Eichrom Technologies, Inc.
The polystyrene beads and THF were obtained from Sigma-Aldrich. All chemicals were
used without further purification.
Figure 2-5 PLF stock solution (A) with un-dissolved polystyrene, (B) with polystyrene completely dissolved
19
Ligand, polystyrene, and THF were weighed with an analytical balance to have
precise amount of chemicals in the stock solution. For each ligand, several stock
solutions were prepared by varying the mass of ligand to examine effect of the ligand
mass on the analyte extraction performance. The amount of polymer in solution was kept
constant at around 2.8g and the mass of ligand was varied from 0.147g to 2.8g. Each
stock solution was described as the ratio between ligand and the entire solid mass. For
example stock solution with one part ligand and one part polystyrene was assigned 1:2
(w/w) ratio. Ligand and polymer mixture was dissolved with about 14g of THF.
2.3.2 Solvent Casting Method
Solvent casting method is the simplest of the three sample preparation techniques.
Most PLFs were prepared by this method. This method is capable of generating a smooth
surface and a uniform thickness PLF with minimum intervention. In this method,
polymer ligand stock solution is directly stippled onto a 33 mm diameter stainless steel
substrate to form a PLF. Roughly about 1 to 1.5 mL of the solution is deposited on a
substrate using this method. THF is highly volatile and polymer starts to solidify in a few
hours after stock solution is stippled onto a substrate. PLFs were placed in a fume hood
overnight to evaporate THF and leaving only solidified film on the substrate. PLFs
prepared with solvent casting deposited about 220 mg of polymer after evaporation of
THF. Figure 2-6 is a 1:5 HDEHP PLF prepared with the solvent casting method.
20
Figure 2-6 PLFs prepared with solvent casting method
The color of PLF generated from this technique differs based on the type of ligand
used and the amount that is mixed into the stock solution. The polystyrene used is clear in
its natural form and the ligand is the only component causing the color change. A large
amounts of ligand in a stock solution generally turns the PLF to a more opaque color
once THF is completely evaporated.
Some PLFs form bubbles along the edge of the film. These bubbles have a
tendency to develop in clear color PLFs. The bubbles are suspected to be from the THF.
It is believed that some of THF is encapsulated in the polymer medium as PLF solidifies.
These THF bubbles are generated on the entire medium and then migrate to the edge and
start combining into a larger size. As the bubble grows in size, it causes polymer film to
expand on the edge as shown in Figure 2-7.
Figure 2-7 Crown ether PLFs with large population of bubbles along the edge
21
Further tests were carried out to test possibility of THF encapsulated on PLF. First, PLFs
were placed under the heat lamp to cause any THF in a polymer medium to boil. The
boiling point of THF is around 65 oC, and temperature under the heat lamp reaches up to
90 oC. Bubbles slowly formed on the PLF once temperature reached around 90 oC.
Bubbles did not migrate towards the edge as observed during PLF preparation. Most
bubbles burst and disappeared as THF escaped from the PLF medium. The second
experiment used a furnace to expedite the formation of bubbles. Temperature was set
around 150 oC and formation of bubbles was faster than when the heat lamp was used.
The bubbles generated in the furnace still only traveled vertically and no horizontal
movement was observed. Both in the heat lamp and furnace experiments, boiling of THF
caused localized expansion of polymer film and unevenness on the PLF surface. The
unevenness of the surface maybe resurfaced by raising the temperature to get polystyrene
to slightly melt and expanded area to re-level. Applicability of thermal resurfacing is
depended on ligand used in the PLF. HDEHP based PLFs work well with this operation.
However, H2DEH[MDP] based PLFs cracked once removed from furnace and cooled.
There are a few limitations in preparing PLF with this technique. First, there are
limited choices of materials that can be used as a backing plate for the film. THF is a
moderately polar solvent, which is capable of dissolving a wide range of nonpolar and
polar chemical compounds. A large amount of THF is used in preparation of PLF, and it
is enough volume to damage any backing material that is dissolvable by THF. This limits
most of the polymer substrates from being used as the backing plate. Figure 2-8 shows
damage caused by THF on nitrile and latex substrates. Also, the large volume of solution
used to generate PLF causes emission of large amount of volatile organic compounds.
22
Figure 2-8 A Latex and Nitrile substrates damaged by THF
2.3.3 Nebulizer Spraying Coating Method
The nebulizer method is developed to prepare a thin PLF by spraying a solution
on a backing material. In this technique, the stock solution is slowly fed into the nebulizer
aperture using a syringe pump, and nitrogen is fed in from the bottom outlet to generate
aerosol droplets of polymer ligand solution as shown in Figure 2-9. The technique is
capable of producing extremely thin film with minimal use of stock solution. The
nebulizer spraying method expands the possibility of applying PLF on many different
shapes and materials. In this method, THF aerosols evaporate instantaneously and only
polymer and ligand reach the substrate, which eliminates the possibility of THF
damaging the substrate.
Figure 2-9 Nebulizer setup for PLF spraying
23
The PLF stock solution was slightly modified to be used with the nebulizer. The
regular stock solution starts clogging the nebulizer capillary after spraying about 4 mL,
causing uneven flow. The stock solution was diluted with THF to make the solution less
viscous to prevent clogging of the capillary. About 40 g of THF was used for 2.2 g of
polystyrene.
The nebulizer used in this experiment was manufactured by Meinhard®. The
nebulizer is rated for up to 1 L/min at 50 psi. The capillary inner diameter is about 0.30
mm. The stock solution is delivered to the nebulizer by KD Scientific syringe pump at a
consistent speed of 150 µl/minute. Nitrogen was passed through the nozzle at 20 psi to
spread PLF stock solution once it left the nebulizer opening. The entire nebulizer
spraying setup is shown in Figure 2-10. The polymer ligand coating was extremely thin
and only 0.012±0.007 g of PLF was used to coat on the 33mm stainless steel substrate.
Figure 2-10 Nebulizer spray coating setup
24
PLF was sprayed on several different substrates ranging from metal to polymer.
THF evaporated instantaneously as the PLF stock solution left the nebulizer nozzle and
polymer ligand mixture formed a web like structure on the substrate as shown in Figure
2-11. Once the entire surface is coated, substrate was placed in a furnace and polymer
was melted to form a film. The PLF on aluminum substrate before and after heat
treatment is shown in Figure 2-11. The polymer coating on the substrate was extremely
thin after the heat treatment. However, the coating was visibly uneven regardless of the
type of substrate used in the process. The control of the spraying apparatus was difficult
to evenly spread the polymer film onto the substrate.
Figure 2-11 Sprayed PLF (A) before heat treatment (B) after heat treatment
2.3.4 Spin Coating Method
The spin coating method is another technique that is capable of producing a thin
circular film on a flat substrate. An excess amount of a solution is placed on the substrate,
which is then rotated at high speed in order to spread the fluid by centrifugal force.
PLFs were prepared by first attaching stainless steel substrate to a spin coater.
Once substrate is securely attached, PLF stock solution is transferred to the substrate then
spun at high speed to spread solution and then remove any excess liquid from the surface.
25
Spin coating conditions were varied to find optimal conditions to generate ideal thin film
for analyte extraction.
Figure 2-12 Uneven polymer film coating on stainless steel substrates by spin coating method
The PLF stock solution used in the experiment was too viscous to evenly spread
over the substrate by high speed spinning. When solution was only dispensed on the
center of the substrate only a section of the substrate was covered as shown in Figure
2-12. Also, swirl pattern can be observed in some samples, which indicates that the spin
speed was too high for the particular solution used in spin coating.
Figure 2-13 PLF spin coating setup
The optimum result was achieved by covering the entire substrate with the PLF
stock solution before spinning the substrate. Any excess liquid was removed by
26
centrifugal force and only a very thin layer was coated on the substrate surface. The
substrate was spun at 750 rpm for 29 seconds. The spin coater is shown in Figure 2-13.
The white spots shown in Figure 2-13 are from the excess PLF solution that was removed
from the substrate. The technique coated 0.013±0.003 g of PLF onto the 33mm stainless
steel substrate. The total PLF mass coated on the substrate was similar to the one
generated with the spray coating method.
2.4 PLF Preparation Conclusions
Several thin film preparation methods were carefully evaluated for the PLF
synthesis. Each technique requires vastly different sample preparation apparatus and
procedures. Out of these techniques, solvent casting, spray coating, and spin coating
were selected and used to prepare PLF. These techniques were simple to implement and
required low initial setup cost. All three methods required use of THF to dissolve ligand
and polymer. Five different ligands were used: bis(2-ethylhexyl) methanediphosphonic
acid, di(2-ethyl hexyl) phosphoric acid, trialkyl methylammonium chloride, 4,4'(5')-di-t-
butylcyclohexano 18-crown-6, and 2-ethylhexyl 2-ethylhexylphosphonic acid.
Polystyrene was exclusively used as a polymer support in this research due to the rigidity
it provides to the PLF and the good alpha spectra resolution achieved with it.
Most of PLFs were prepared with the solvent casting method due to its ability to
easily scale up the production. PLFs prepared using this technique had uniform thickness
and very smooth surface. The color of PLF generated with solvent casting differs based
on the ligand and the ligand to polymer ratio. A relatively large volume of 1mL of stock
27
solution was used to prepare a PLF. The large volume of THF limits choice of backing
substrate that can be used with the method. Most polymer substrates are incompatible
with THF. Also, there were several indications that THF was encapsulated in polymer
medium as PLF solidifies. THF was so volatile that it evaporated and formed a solid
polymer layer on the top and prevented complete evaporation of solvent from the
polymer structure.
The nebulizer spray coating method expands the possibility of applying PLF on
various types of surfaces. In this method, THF aerosols evaporate instantaneously and
form a web like structure on the substrate. Once the entire surface was coated, substrate
was heat treated to melt the polymer to form a film. The polymer coating on the substrate
was extremely thin after the heat treatment. However, the coating was visibly uneven.
The spin coating method was also able to generate extremely thin polymer films. An
excess amount of stock solution was removed with centrifugal force and only thin film
was left on the substrate. Both the nebulizer spray coating and spin coating methods
deposited similar mass of PLF on the stainless substrate. , which indicates a similar film
thickness.
PLFs prepared in this chapter were tested for analyte extraction in various
conditions. Plutonium was mostly used to test PLFs. Detailed information of each PLF is
discussed in following three chapters.
28
3. Chapter 3
Bis(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP])
3.1 Introduction
Bis(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP]) ligand based PLFs
were studied for plutonium and uranium extraction. H2DEH[MDP] was chosen as an
extractant due to its ability to extract actinides over a wide range of acid concentrations.
PLFs were examined in a wide range of conditions for plutonium and uranium extraction.
3.2 Theory and Background
Diphosphonic acids are known for their ability to form strong complexes with
metal ions through ionized phosphonic acid groups and P=O groups [36]. Bis(2-
ethylhexyl) methanediphosphonic acid (H2DEH[MDP]), which contains the diphosphonic
group, is known to effectively retain alkaline earth metals and actinides, particularly for
tetra and hexavalent oxidation states [37], [38]. This extractant is synthesized by mixing
one equivalent of MDPA and two equivalents of 2-ethylhexanol in dry tetrahydrofuran
(THF). The mixture is refluxed and a solution of dicyclohexylcarbodimide is added
dropwise over a period of three hours. The solution is refluxed for three more days. The
crude product is obtained by evaporating the solvent under reduced pressure. Further
purification is done by dissolving the crude product in warm 1 M ammonium hydroxide
and impurities are extracted with CH2Cl2. HCl is then added to adjust pH to below 1 and
a purified compound is extracted with CH2Cl2 [39]. The chemical structure of Bis(2-
29
ethylhexyl) methanediphosphonic acid (H2DEH[MDP]) is shown in Figure 3-1.
H2DEH[MDP] is a clear and extremely viscous oil that is insoluble in water, but soluble
in organic diluent [37], [38], [40]. The two phosphoryl groups in the extractant are very
effective in retaining actinides, particularly for tetra and hexavalent oxidation states [37],
[38].
Figure 3-1 Chemical structure of H2DEH[MDP]
H2DEH[MDP] exists in dimeric form in organic diluents. Dimerization is
achieved by displacement of H+ ion from the H2DEH[MDP] molecule and through strong
hydrogen bond interaction between the phosphoryl and P-OH groups [41].
Studies have shown that selectivity of H2DEH[MDP] among the alkaline earth
metal ions is independent of acidity [39], [41]. Alkaline earth metals are extracted from a
solution by two dimeric H2DEH[MDP] molecules. The alkaline metal is captured by a
number of six-membered chelate rings through metal and P=O bonds in the center of a
complex molecule as shown in Figure 3-2 [39].
30
Figure 3-2 Alkaline earth metal extraction mechanism with H2DEH[MDP]
Am(III) is also extracted in a similar manner with the metal ion bonded to two
dimeric extractants and with three H+ ions displaced to neutralize the charge on the metal
ion [41]. The exact extraction chemistry for Fe(III), U(VI), and Th(IV) has not been
reported. It is only expected to be more complicated than alkaline earth metals and
Am(III).
H2DEH[MDP] is used by Eichrom Technologies, Inc. to manufacture their
Acinide® resin. The resin is produced by coating H2DEH[MDP] onto 20-50 um size
Amberchrom CG-71ms acrylic ester resin beads [37]. The main application for this
particular resin is for group actinide separations and gross alpha measurements. The
manufacturer’s data on this resin shows extremely high k’ for Am(III), Pu(IV), Th(IV),
Np(IV), and U(VI) as shown in Figure 3-3 [42]. The high k’ is an indication that
extractant has high affinity for that particular analyte.
31
Figure 3-3 H2DEH[MDP] distribution ratio dependency on HCl concentration for various ions
3.3 Plutonium and Uranium Extraction
H2DEH[MDP] based PLFs were tested for plutonium extraction in various
conditions. Several different ratio PLFs were first tested over various nitric acid
concentrations. The amount of ligand plays a critical role in extraction capability and
integrity of PLF. Also, the extraction of analytes using ligands showed high dependency
on the pH in liquid/liquid extraction. Since the ligands are incorporated into a polymer
support matrix, the extraction dependency on solution pH may differ from liquid/liquid
extraction cases. It is important to find the optimal amount of ligand that will provide the
best analyte extraction and at the same time provide a robust film structure.
32
3.3.1 Analyte Extraction Characterization
1:5, 1:10, and 1:20 ratio H2DEH[MDP] PLFs were tested over 0.01 to 8M nitric
acid solutions to generate baseline plutonium extraction performance. 1:2 PLF was also
prepared for the study, but it was not structurally robust to use with the nitric acid. 239Pu
solutions used in this study were prepared with 0.01, 0.1, 1, or 8M nitric acid solution.
Plutonium tracer solution was first dried on a hot plate then re-dissolved in a
concentration adjusted nitric acid solution. For the PLF testing, 2.5 to 3mL 239Pu tracer
was directly stippled on the PLF surface, allowing the analyte to equilibrate for 3 hours
before removing the solution. Solution volume was selected to cover the entire PLF
surface. Some of the tracer solution evaporated during the equilibration time but left
anywhere from 1 to 2 ml solution on the PLF substrate. Tracer solution left on the PLF
was collected and electrodeposited to measure plutonium activity left in the solution.
After removing the tracer solution, PLFs were thoroughly rinsed with deionized water to
remove any nitric acid remaining on the surface and to remove any tracer that was not
bound to the surface. PLFs were then allowed to air dry to remove any water that may
have been left on the polymer medium. The plutonium activity of each sample was
measured by direct alpha counting to quantify the plutonium recovery by H2DEH[MDP]
PLF.
Octet Plus system from Ortec, equipped with 900 mm2 ion implanted silicon
detectors, was used in the entire experiment performed in this study. The vacuum
chambers can accept sample size up to 51mm and chambers were large enough to accept
all PLF samples. However, the sample tray provided with the detector system was not
33
designed for the PLF analysis. PLFs could not be secured to the tray and it had a
tendency to move out of position when vacuum was applied. This might cause inaccurate
activity measurement as the sample would move out of the detector line of sight. Also,
the consistency of the PLF placement relative to the detector could not be ensured in this
setup. This caused inconsistent activity measurement from sample to sample. The sample
trays were modified by cutting a hole in the middle to have the PLF substrate sit securely
on the tray. This modification eliminated sample movement during the analysis and
increased the consistency in sample analysis condition. The modification ensured
consistent sample placement in the vacuum chamber and also provided easier sample
handling. The picture of the sample tray before and after the modification is shown in
Figure 3-4.
Figure 3-4 Alpha spectroscopy sample tray (A) before modification (B) after modification
The plutonium recovery by H2DEH[MDP] PLF showed a dependence both on the
nitric acid concentration and the composition of the polymer film. H2DEH[MDP] PLF
34
was able to extract plutonium in all nitric acid concentration tested as shown in Figure
3-5. Both 1:10 and 1:20 PLFs were effective for plutonium extraction from 0.01 to 1M
nitric acid. There was no statistical difference in plutonium recovery between 1:10 and
1:20 PLF at each nitric acid concentration from 0.01 to 1M. The highest recovery for
both PLFs occurred at 1M tracer solution. The percent recoveries were 50.44±8.27 and
47.61±7.17 for 1:10 and 1:20 PLF, respectively. The plutonium recovery for 1:5 PLF was
noticeably lower than the other two from 0.01 to 1M. However, the recovery was higher
at 8M than other two PLF types tested.
Figure 3-5 The baseline performance of H2DEH[MDP] PLF in plutonium extraction as a function of nitric acid concentration
The plutonium extraction study was further expanded to include other PLF compositions
to have more detailed picture on the role of the composition in the extraction efficiency.
1:15 and 1:25 PLFs were prepared and tested in same manner as other H2DEH[MDP]
PLFs. 1:15 PLF followed the plutonium extraction trend shown by 1:10 and 1:20 PLFs.
Figure 3-6 shows a similarity of 1:10, 1:15, and 1:20 PLFs in plutonium extraction. 1:25
0
10
20
30
40
50
60
70
0.01 0.1 1 10
Pu re
cove
ry (%
)
Nitric concentration [M]
1:5
1:10
1:20
35
PLF was unstable and showed tendency to develop large bubbles while in the vacuum
chamber of the alpha spectroscopy system. 1:25 PLF with large bubbles is shown in
Figure 3-7. About 90% of 1:25 PLFs developed bubbles and in some cases polymer film
shattered into pieces. The bubbles were believed to be caused by gas trapped in the
polymer structure, most likely THF. Larger ligand content in PLF is believed to provide
more porous surface for gas to escape from the polymer structure. In 1:25 PLF, which
contain lowest amount of ligand, large amount of gas is being trapped during PLF
synthesis due to inadequate venting. Once vacuum was applied trapped gas in PLF
ballooned the surface as it escapes from polymer structure. Due to the stability issue, 1:25
data was not included in Figure 3-6.
Figure 3-6 Plutonium recovery by 1:10 through 1:20 H2DEH[MDP] PLF as a function of nitric acid concentration
0
10
20
30
40
50
60
70
0.01 0.1 1 10
Pu re
cove
ry (%
)
Nitric concentration [M]
1:10
1:15
1:20
36
Figure 3-7 1:25 H2DEH[MDP] PLF with damaged surface
It was expected for 1:5 H2DEH[MDP] PLF to have the highest recovery due to
higher number of ligands presented in the PLF compared to 1:10, 1:15, and 1:20 PLFs.
Ligand is the only component within the PLF to have any significant affinity to
plutonium and the more ligands means more binding sites for plutonium. This result
clearly shows that the plutonium extraction is not only dependent on the amount of ligand
presented in the PLF but many other factors, such as ligand orientation, ligand
complexation, and plutonium oxidation state. Plutonium has five oxidation states, and up
to four different oxidation states can co-exist in a solution [43]. It was impossible to
measure the plutonium oxidation states in the solutions used in the experiment due to low
plutonium quantity in each solution. However, it is suspected that both +3 and +4
oxidation states co-exist in the tracer solution [43]. The H2DEH[MDP] have shown
effectiveness in both Pu(III) and Pu(IV). The H2DEH[MDP] ligands are theorized to
form various length complexes with each other as the PLF is synthesized and plutonium
extraction behavior changes based on the length of the complex. This means that certain
complexes are only effective for Pu(III) extraction, and the other complexes are only
effective for Pu(IV). More ligands in the stock solution seems to cause H2DEH[MDP] to
37
form complexes that are mostly effective for Pu(IV) extraction. As the amount of ligand
in the stock solution decreases, two distinctive ligand complexes form, one for Pu(III)
and the other for Pu(IV). Another possible explanation for the plutonium extraction
behavior observed is that nitric acid is changing the orientation of ligands to be more
favorable for plutonium extraction at certain nitric acid concentrations. For example,
ligands in 1:10, 1:15, and 1:20 PLFs are oriented more favorably for plutonium extraction
at 0.1 or 1M nitric acid.
Tracer solutions left on the PLFs were collected after 3 hour exposure to measure
plutonium activities that were not extracted by PLFs. Each sample was traced with 242Pu
and electrodeposited for the analysis. Samples were prepared on 5/8 inch stainless steel
substrates using sulfuric acid based electrolytes. The addition of plutonium recovered
from the PLF and the electrodeposited sample was expected to be close to 100%;
however, in most samples, the recovery was below 100%.
Figure 3-8 Unaccounted plutonium by H2DEH[MDP] PLF as function of nitric acid concentration
0
10
20
30
40
50
60
70
0.01 0.1 1 10
Pu re
cove
ry (%
)
Nitric concentration [M]
1:5
1:10
1:20
38
Unaccounted plutonium activities are plotted and shown in Figure 3-8. About 20 to 40%
of the activities were unaccounted for PLFs tested with 0.01 to 1M nitric acid. There was
no missing activity dependency based on the PLF compositions from 0.01 to 1M nitric
acid. PLFs tested with 8M nitric acid, however, showed considerably different behavior
than ones tested with 0.01 to 1M. With 8M nitric acid, unaccounted 239Pu activity
increased as a function of ligand mass in PLF. Figure 3-9 was prepared with only 8M
nitric acid data to better show the changes in missing activities by different composition
PLFs.
Figure 3-9 Unaccounted plutonium activity with 8M nitric acid
It is inevitable that some activity will be lost during the sample preparation
process due to multiple solution transfer involved in the procedure. However, the missing
activities are too great to be only associated to the activities lost during the sample
preparation. The missing plutonium activities observed for samples are most likely
caused by analyte depositing below the surface of a PLF. Plutonium deposited below the
surface will not be measured by alpha spectroscopy due to the heavy charged particle
39
interactions causing energy from alpha particles to be absorbed by PLF. The total activity
deposited on the H2DEH[MDP] PLF will most likely be higher than the one measured
with alpha spectroscopy.
There are two possibilities on how the plutonium is deposited below the surface.
The first possibility is tracer solution penetrating through the space between the stainless
steel substrate and the PLF body. The second possibility is that PLF is permeable to the
nitric acid solution and plutonium is depositing on the entire polymer body. It is
important to know the penetration mechanism to control or manage the overall analysis.
Figure 3-10 Plutonium penetration mechanism experiment by varying tracer solution volumes
The penetration mechanism was studied by varying plutonium tracer volume
stippled onto the PLF to adjust area covered by the tracer solution. Three different
volumes, 1, 2, and 3 mL, were used in the study. Figure 3-10 shows how much surface
the tracer solution covered at different solution volumes. 1 mL of tracer solution covered
only a portion of the PLF surface, and it stayed away from the edge of the PLF. 2 mL
solution also only covered a portion of the surface, but some of solution touched the edge.
The largest volume used, 3mL, was able to cover the entire surface. Each sample was
prepared in an identical condition except for the tracer volume. Any tracer left on the PLF
surface was collected after exposure. The collected tracer solution was electrodeposited
onto a 5/8 inch stainless steel for alpha spectroscopy. Plutonium activity deposited on the
surface and activity left on the tracer solution were listed in Table 3-1. Assuming that
most missing activity was deposited on the PLF medium, it is shown that the normalized
40
penetration activity has no dependence on the tracer solution volume. This result
indicates that analyte was penetrating through the entire PLF surface, and there was no
gap between the stainless steel substrate and the PLF to allow analyte penetration.
Table 3-1 Plutonium penetration dependency on solution volume Solution Volume
(mL) PLF Recovery (%) Electrodeposition
Recovery (%) Unaccounted Activity (%)
1 28.19±4.75 19.15±2.92 52.66±3.53 2 28.87±4.20 19.90±2.23 51.23±1.97 3 29.21±8.63 14.49±3.19 56.30±5.55
This phenomenon of analyte depositing through the depth of the PLF gives one
major advantage in destructive analysis, such as mass spectroscopy. The PLF technique is
developed as a screening method and the goal is to perform destructive analysis on
selective samples to gain much needed isotopic information in the shortest possible time.
Larger amounts of analyte present in the PLF gives better chance of performing precise
analysis to gain analyte isotopic information. Figure 3-11 is a schematic view of
radionuclides extraction by PLF, where analytes are depositing on surface and throughout
the depth of the film.
Figure 3-11 Schematic diagram of PLF analyte extraction mechanism
41
One of the possible issues arising from analyte penetrating phenomenon is the
potential for degradation of alpha spectrum. The alpha spectrum resolution is extremely
dependent on the quality of the source. In most cases, the best resolution is achieved with
clean, thin, and uniform layer samples. Multi-layer samples tend to have a broad
spectrum peak due to a source self-attenuation. The spectrum resolution from the PLF
was compared to the resolutions attained with electrodeposited samples to measure the
effect of analyte penetration on the spectral resolution. The spectra were analyzed by
fitting the peaks with Bortels’ equation, which is given in Equation 3.1.
𝑓(𝑥) = �ℎ𝑖𝜎√2𝜋
2𝜏𝑒𝑥𝑝 �
𝑥 − 𝜇𝑖𝜏
+𝜎2
2𝜏2� 𝑒𝑟𝑓𝑐 �
1√2
�𝑥 − 𝜇𝑖𝜎
+𝜎𝜏��
𝑛
𝑖=1
Equation 3.1
where n is number of peaks, μ is the mean, σ is the standard deviation, τ is the distortion,
and h is the height of a peak. The resolution of the detector systems was determined by
measuring a full width at half maximum (FWHM) of the peak. The FWHM was
calculated from the Gaussian width or standard deviation of the peak using Equation 3.2.
The FWHM and distortion term, τ, were used to compare peak broadening.
𝐹𝑊𝐻𝑀 = 2√2𝑙𝑛2𝜎 ≈ 2.35𝜎 Equation 3.2
All four H2DEH[MDP] PLF compositions showed similar FWHM and distortion in the
nitric acid range tested as shown in Table 3-2. Variations in peak fitting terms between
samples were low, which indicate consistent peak shape between samples. The resolution
and distortion were comparable to the one achieved with a typical electrodeposition
sample.
42
Table 3-2 Average FWHM and Tailing for H2DEH[MDP] PLFs tested for plutonium extraction PLF ratio Nitric Acid (M) FWHM (keV) Tailing 1:5 0.01 19.42±1.08 23.70±2.18 1:5 0.1 18.81±1.39 24.63±0.69 1:5 1 19.35±2.94 28.20±2.40 1:5 8 12.74±1.62 24.72±1.02 1:10 0.01 19.86±1.50 20.49±1.76 1:10 0.1 18.44±0.83 21.48±0.34 1:10 1 18.81±2.01 21.48±0.98 1:10 8 20.71±2.49 24.49±4.46 1:15 0.01 24.71±3.83 19.35±2.83 1:15 0.1 25.94±1.44 21.03±1.20 1:15 1 26.51±1.54 20.11±0.88 1:15 8 23.83±6.60 17.90±1.17 1:20 0.01 19.99±2.70 19.90±2.49 1:20 0.1 21.15±1.65 19.22±1.01 1:20 1 17.89±2.18 19.83±0.72 1:20 8 18.42±3.68 14.52±3.34
1:10, 1:15, and 1:20 PLFs were all suitable for plutonium extraction. Out of three
compositions, 1:20 used the least amount of H2DEH[MDP] ligands to manufacture PLFs,
which makes it more cost effective. Due to the cost saving, 1:20 PLF was more closely
inspected for plutonium extraction.
3.3.2 Time Dependency Test
The equilibration time of 3 hours was used in the previous section to generate a
baseline for plutonium extraction behavior for the H2DEH[MDP] PLF. The time was
chosen to provide enough time for ligands to form complexes with the plutonium.
However, the PLF method is being developed to rapidly process samples and shorter
equilibration time is always preferred. It is important to examine plutonium extraction
43
dependency on equilibration time to decrease analysis time. In this experiment, 1:20
H2DEH[MDP] PLF was tested with 0.1M nitric acid.
The extraction condition was kept consistent throughout the experiment except for
the exposure time. The exposure times used in this experiment were from 10 to 180
minutes. The plutonium recovery linearly increased from 10 to 90 minute exposure time
then started to level off after 90 minute exposure time as shown in Figure 3-12. The
maximum plutonium recovery of 44% was achieved at 180 minute equilibration time.
However, the standard deviation at 180 minute exposure time was larger than other
measurements. 90 min and 120 min recoveries were within the standard deviation of the
180 min recovery. Student’s t-test was performed to confirm and assess the statistic
difference between plutonium recoveries between 90 to 180 minutes. The recoveries
measured at 90 and 120 min exposure time was statistically indifferent from the 180 min
measurement at 95% confidence level.
Figure 3-12 H2DEH[MDP] PLF plutonium recovery at different exposure time
44
The most important aspect that can be gathered from this time study is that the
PLF was able to extract plutonium even at 10 min equilibration time. The recovery was
only slightly higher than 10%, however, even 10% may provide sufficient activity to
perform a radiometric analysis depending on the sample activity. In a post-detonation
situation, sample activity near ground zero will be high enough for even a very short
equilibration time to extract enough plutonium for a radiometric analysis. In the case of
an environmental sample, which will typically have low activity, 10% recovery most
likely will not provide enough analyte for reliable radiometric analysis. However, if the
PLF technique is only used as a screening method before performing a more precise
analysis, this technique can be utilized to decrease total sample numbers and shorten the
total analysis time. Alpha spectroscopy can be used to measure any plutonium activity
above background level and plutonium can then be back-extracted from a PLF for mass
spectroscopy. The mass spectroscopy analysis only requires a trace amount of plutonium
to reliably perform an isotopic measurement. In the case of Thermal Ionization Mass
Spectroscopy (TIMS), approximately 100 femtogram of plutonium is needed for analysis
with a routine sample preparation method. The detection limit can be even lower with
more sophisticated sample preparation methods, such as resin bead loading, carbonized
filament, and etc. 100 femtogram of 239Pu translates to about 1.399x10-2 dpm, and other
plutonium isotope activities are listed in Table 3-3. Silicon alpha detectors are not
sensitive to measuring any decay energy given from plutonium isotopes listed in Table
3-3. TIMS analysis can be reliably performed if any activity is measured from the sample
using alpha spectroscopy.
45
Table 3-3 Plutonium activities per 100 fg of analyte Plutonium Isotope Alpha Activity for 100 fg analyte(dpm) 239Pu 1.399x10-2 240Pu 5.106x10-2 242Pu 8.880x10-4
3.3.3 Consistency Study
It is enormously important to have consistency in analyte recovery for PLFs to be
used as a reliable sample preparation method. The recovery does not necessary have to be
high but it must be consistent and reproducible. There are two main possible causes for
the inconsistent PLF plutonium extraction efficiency. The first source of the inconsistent
analyte extraction is due to variability in PLF itself. The second possible cause of the
inconsistency is the plutonium oxidation state discrepancy between tracer solutions. The
plutonium oxidation effect on extraction efficiency was already discussed in 3.3.1
Analyte Extraction Characterization section in this chapter. There may also be a small
inconsistency in activity measurement resulting from a counting uncertainty. However,
measurement variation due to the counter system should be minimal compared to PLF
variation or plutonium oxidation variation.
The data from the previous experiments showed a large standard deviation from
1:20 PLFs that were tested with 0.1M tracer solution for 3 hour equilibration time. This
high variation could have been a result of either PLF variation or oxidation state
difference in solutions used. The PLFs used in previous experiments were prepared and
used as needed and so were the 239Pu tracer solutions. In other words, no controlled
experiment was carried out to carefully test the PLF consistency. The plutonium
46
oxidation states are hard to control in a real world situation and the focus was on
examining the consistency of the PLF itself.
The experiment was designed to test the PLF consistency with 1:20
H2DEH[MDP] PLF and 0.1M nitric plutonium tracer solution. For this experiment, two
1:20 H2DEH[MDP] PLF stock solutions were prepared on a different date. The stock
solutions were carefully prepared to minimize inconsistency. The amounts of each PLF
component used in the stock solutions are listed in Table 3-4. These two stock solutions
were used to synthesize two batches of PLFs. There was no visible difference between
two batches of PLFs as shown in Figure 3-13.
Table 3-4 Mass of components used to prepare two H2DEH[MDP] PLF batches for the consistency study Batch 1 Batch 2 H2DEH[MDP] (g) 0.291 0.298 Polystyrene (g) 5.672 5.586 THF (g) 28.105 28.013
Six PLFs from each batch were selected for the experiment; a total of 12 samples were
prepared by stippling 3 ml of 0.1M 239Pu tracer solution on each PLF. The standard
equilibration time of three hours was used in the experiment. Each sample was counted in
six different detectors to measure 239Pu activity deposited on the PLF. Samples were
counted in multiple detectors to measure activity variability caused by the detector
system.
47
Figure 3-13 H2DEH[MDP] PLFs from two batches
The plutonium recoveries by PLFs are plotted in Figure 3-14. There were slight
differences in activities measured as samples were counted by six different 900 mm2
alpha detectors. However, as shown in Figure 3-14, the trends were similar for all
detectors; the plutonium recovery for sample 5 was considerably lower than other
samples. Sample 5 was deemed an outlier, and it was excluded from the data analysis.
Figure 3-14 Plutonium recoveries by two different batch 1:20 H2DEH[MDP] PLFs with 0.1M nitric acid solution
15.00
20.00
25.00
30.00
35.00
40.00
45.00
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Plut
oniu
m R
ecov
ery
(%)
Sample #
Detector1
Detector2
Detector3
Detector4
Detector5
Detector6First set Second set
48
The variability between the batches was examined by computing the plutonium
percent recovery mean from six PLFs from each batch as shown in Table 3-4. The second
batch consistently showed higher recovery than the first batch, but the values were within
the standard deviation. Based on this data, the plutonium recovery was not significantly
different from the first batch to the second batch. The overall plutonium recovery showed
about 16 to 17.5% standard deviations in this experiment depending on the detector.
Table 3-5 Average plutonium recovery by each batch First Batch Second Batch Overall
Detector 1 33.12±3.30% 36.34±4.12% 35.23±3.25% Detector 2 33.19±3.23% 35.43±3.57% 34.76±3.64% Detector 3 35.16±3.03% 38.51±3.54% 37.36±3.75% Detector 4 32.48±3.64% 37.56±3.73% 35.61±4.52% Detector 5 32.09±2.33% 36.75±3.85% 34.98±4.03% Detector 6 32.87±3.56% 36.53±3.38% 35.22±3.95%
The PLF method was developed to be used as an alpha source preparation
method. It is important to compare PLF standard deviation to the standard deviation
normally observed in an electrodeposition sample preparation, since the electrodeposition
method is the most widely used alpha source preparation technique. Ten electrodeposited
239Pu samples were carefully prepared and samples were counted under the 450mm2
alpha particle detectors. The electrodeposited samples had about 17.6% standard
deviation, which was very similar to one observed from the PLF method.
The total surface plutonium recoveries by H2DEH[MDP] PLF were consistently
lower than one observed with combination of column separation and electrodeposition.
However, H2DEH[MDP] PLF is capable in providing consistent plutonium recovery that
are similar to the consistency seen in electrodeposition samples.
49
3.3.4 Blind Study
All of the previous sections looked into characterizing PLF behavior in plutonium
extractions. Only known activity samples were processed and analyzed with alpha
spectroscopy. An experiment was designed to verify ability of H2DEH[MDP] PLF to
process unknown samples and pin point the activities of the samples. Six unknown 239Pu
samples were prepared by a third person with no activity indication on beakers. Each
sample was traced with 242Pu then dried on a hotplate. Once samples were all dried, those
were brought back up with 3mL of 1M nitric acid. Each sample was directly stippled on
to 1:20 H2DEH[MDP] PLF and equilibrated for 3 hours. These samples were directly
counted with alpha spectroscopy for 24 and 96 hours. Once data was processed, the
measured activity of each sample was compared with the actual activity.
Table 3-6 Plutonium activity measurements from blind samples using 1:20 H2DEH[MDP] PLF
Known Activity (dpm) 24 hour counting (dpm)
96 hour counting (dpm)
Sample 1 17.86±1.12 19.03±0.47 17.49±0.33 Sample 2 8.88±0.57 7.65±0.32 8.56±0.21 Sample 3 8.83±0.56 8.23±0.28 9.05±0.20 Sample 4 0.00 0.02±0.03 0.01±0.01 Sample 5 3.30±0.23 4.37±0.19 4.27±0.12 Sample 6 1.72±0.15 1.62±0.14 1.78±0.08
The 96 hour counting time gave more accurate measurement as expected. Every
measurement was within the uncertainty of the true activity except for sample 5 as shown
in Table 3-6. In the 24 hour count, activity measurements from sample 2 and 5 were
slightly outside of the true activities. The activity measurements from sample 5 were
consistently higher than the true value in both 24 and 96 hour counting. Sample 5 was
counted in different detectors to eliminate possible systematic error caused by the
50
counting system. The detector system itself was not the cause of the deviation in
measurement. The inaccurate measurement could have been a result of inconsistent
delivery of 242Pu tracer solution. The tracer solution was volumetrically measured and
delivered using micro-pipette. There is a higher degree of uncertainty involved with
volumetric measurement compared to the gravimetric measurement. There is also a small
possibility of unknowingly delivering inaccurate volume with a pipette.
The blind test proves that the PLF system can be effectively used to process
unknown samples. It is important to point out that tracer recovery was significantly lower
than the electrodeposition method. For six samples processed with PLF in this
experiment, 20-28% tracer recoveries were observed. The tracer recoveries with
electrodeposition are normally around 80 to 90%. Even with this inherent limitation, PLF
system was able to pin point the activities of samples ranging from 0 to 18 dpm.
3.3.5 Alternate PLFs
Three PLF preparation methods were used to synthesis PLF samples. These
preparation methods are described in Chapter 2. Most of the experiments were carried out
with PLFs prepared by the solvent casting method. Data gathered from the solvent cast
PLF was used as a starting point in studying spray coated PLF and spin coated PLF for
plutonium extraction. Two main aspects were examined in this section: effectiveness of
alternate PLFs in plutonium extraction and effects of alternate PLFs on the alpha spectra
resolution.
51
The spray coated 1:10 H2DEH[MDP] PLFs were used to test for plutonium
extraction with 239Pu tracer solutions prepared with 0.1M nitric acid. In spray coating,
only about 12 mg of polymer film is being deposited on a stainless substrate compared to
about 220 mg for solvent casting method. The amount of ligands on the surface of the
film is similar in both spray coating and solvent casting. However, overall quantity of
ligands in the film is obviously lower for spray coated PLF than one prepared by solvent
casting. The plutonium recovery with spray coated PLF was lower compare to solvent
casting PLFs. Only 1.81% of 239Pu was extracted from 0.1M nitric acid.
One possible application of spray coating method is to prepare PLF on alternate
substrates and/or non-standard shape substrates. One of the examples is preparing a PLF
on an 8 x 10 inch aluminum foil. The increase in total surface area provides larger and
more active sites for analyte extraction on the surface. This provides a better PLF design
to be used for analyte extraction from a large volume. One limitation of the large
substrate is that PLF becomes too big to place in an alpha spectroscopy vacuum chamber,
which eliminates any possibility of direct sample analysis. However, destructive analysis
still can be performed to quantify plutonium extracted with such setup.
The PLFs prepared using the spin coating method have similar masses as the
PLFs prepared with the spray coating method. The surface was noticeably smoother than
the one prepared with the spray coating. 1:20 PLFs were tested for plutonium extraction
with the tracer solutions prepared with 0.1M nitric acid. About 30.61% of 239Pu was
recovered by the spin coated PLFs. Tracer solution left on PLFs were collected and
electrodeposited to measure any plutonium that may have penetrated through the PLF.
About 53.80% of activity was unaccounted for, which was highly likely to have been
52
deposited below the surface. The surface activity for spin coated PLF was about 13%
lower than one seen with the solvent casted.
3.4 Digital Autoradiography
Digital autoradiography is a great tool to study distribution of radioactive particles
on a sample. This technique works the same way as a conventional radiography except
that the process is digitized for convenience. The digitization of the entire process
eliminates a need for a darkroom and a need for developing a film using chemicals. This
saves time from exposure to analysis.
Samples were placed on an imaging plate (Fujifilm BAS-TR 2025) and kept in a
lead shielded cave for 24 to 48 hours depending on the sample activity. This particular
imaging plate is about ten to one hundred times more sensitive than film, which decreases
exposure time considerably compared to the conventional film [44]. Once the imaging
plate was removed from the sample, it was then digitally scanned using GE Typhoon
FLA 7000 system. The radiography image in Figure 3-15 was generated after 24 hour
exposure and the locations of plutonium were clearly visible over the background. The
image generated with the digital autoradiography was mathematically analyzed using
computer programs to more closely study the plutonium distribution.
53
Figure 3-15 Digital autoradiography image from 1:20 H2DEH[MDP] PLF
The image was first imported into ImageJTM software to analyze plutonium
locations. The location of every particle in the image was recorded in a Cartesian
coordinate system. The particle distribution was studied by importing the coordinates
from ImageJ to the in-house developed particle distribution analysis software. The source
code is attached in Appendix A. The code was developed in C++ language in Microsoft
Windows® environment. The software divides the image into rectangular bins and counts
particles in each bin. The bin size was adjusted to give an average of 40-50 counts per bin
to achieve about 15% uncertainty in each bin. The plutonium distribution maps were
created from the processed data. Eight samples shown in Figure 3-15 were all processed,
and it all showed uneven plutonium distribution with hot spots as shown in Figure 3-16
and Appendix B.
54
Figure 3-16 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image
The location of hot spots were different from sample to sample. PLF samples were
prepared in the same condition, and percent plutonium recovery showed little difference
between samples. It is strongly suspected that local hot spots were originated from the
PLF itself. These hot spots may be the result of high localized concentration of ligands or
surface defects. Plutonium may preferentially deposit around a defect due to a surface
area increase. Also, the ligands in a defect area may be oriented in such a way that it is
more favorable for plutonium extraction.
3.5 Uranium Analysis
H2DEH[MDP] was designed for an actinide group separation and also showed
high affinity for uranium. Since uranium alpha spectra peaks are well separated from
plutonium peaks, it is possible to co-extract plutonium and uranium onto PLF then
perform alpha spectroscopy to qualify. PLFs were examined for uranium extraction using
a natural uranium tracer. Uranium stock tracer information is given in Table 3-7.
55
Table 3-7 Uranium tracer activity information Uranium Isotope Activity (Bq/g)
238U 5.694±0.108 235U (2.620±0.050)x10-1 234U 5.580±0.106
The condition tested for uranium extraction was the same as the baseline
plutonium experiment; 1:5, 1:10, and 1:20 H2DEH[MDP] PLFs were tested over 0.01 to
8M nitric acid solutions. The uranium extraction behavior was entirely different than the
plutonium extraction. Neither 1:10 nor 1:20 PLF was effective in uranium extraction over
all nitric acid ranges tested. 1:5 PLF showed the highest recovery of ~30% with 1M nitric
acid as shown in Figure 3-17. Also, about 22.5% of uranium was extracted using 1:5 PLF
at 0.1M nitric acid. Data shows that H2DEH[MDP] PLF can be used to selectively extract
plutonium over uranium or simultaneously extract uranium and plutonium by changing
the composition of the PLF. For example, with 1:5 PLF, uranium can be co-extracted
along with plutonium at 0.1 or 1M nitric acid. At the same nitric acid concentration, 1:20
PLF can be used to extract plutonium over uranium.
Figure 3-17 Uranium recovery by H2DEH[MDP] PLF as function of nitric acid concentration
0
5
10
15
20
25
30
35
0.01 0.1 1 10
U re
cove
ry (%
)
Nitric concentration [M]
1:5
1:10
1:20
56
The analyte selectivity based on PLF composition was further verified in the co-
extraction experiment by using mixed uranium and plutonium tracer solution. The mixed
tracer solution was prepared by drying 239Pu and natural uranium then re-dissolved in 1M
nitric acid. The standard PLF testing procedure was used with the mixed tracer solution.
4.95 dpm of plutonium and 5.24 dpm of uranium were used to prepare each sample.
The experiment confirmed that H2DEH[MDP] PLF is capable of co-extracting or
selectively extract plutonium over uranium depending on the PLF composition.
Plutonium and uranium percent recovery by each PLF is shown in Figure 3-18. With 1:5
PLF, about 23% of plutonium and 20% uranium were simultaneously extracted. Opposite
to 1:5, both 1:10 and 1:20 PLFs were preferably extracting plutonium over uranium.
Figure 3-18 H2DEH[MDP] PLF Pu and U extraction efficiency with 1M nitric acid
3.6 Mass Spectroscopy Analysis
The plutonium isotopic ratio provides critical information on the origin and
intended use of the material. Alpha spectroscopy can offer some degree of isotopic
0
10
20
30
40
50
60
1:5 1:10 1:20
Reco
very
(%)
Dipex PLF ratio
Pu
U
57
information; however, it has limitations due to its resolution. For instance, 240/239Pu
measurement is impossible to make with alpha spec due to the closeness of its peaks.
This limitation is why plutonium isotopic measurements are made using mass
spectroscopy, mainly with Thermal Ionization Mass Spectrometry (TIMS). The final goal
of this project is to develop a screening method to rapidly process samples for
radiometric analysis then further perform destructive analysis on selective samples to
gain more precise measurement. This involves first back-extracting analyte of interest
from the PLF and process samples for the TIMS analysis.
Several experiments were performed to back-extract plutonium from
H2DEH[MDP] PLF substrates and perform TIMS analysis. For PLF samples, it is
essential to effectively back-extract plutonium from PLF to perform TIMS analysis.
Several different reagents were used to back-extract plutonium, including nitric acid,
deionized water, and isopropanol.
Once plutonium was back-extracted from the PLF, GV Instruments IsoProbe-T™
Multi-Collector Thermal Ionization Mass Spectroscopy (TIMS) was used for the
analysis. The system is equipped with a multiple-Faraday/ion-counting collector
assembly for precise isotopic measurement. Generally about 200 femtogram of sample is
needed to measure the plutonium isotopic ratio with techniques that was used in this
research.
58
3.6.1 Back-extraction with Nitric Acid and Deionized Water
The uptake of plutonium by H2DEH[MDP] has some dependency on acid
concentration. Based on Horwitz et al., the plutonium uptake decreases as concentration
of hydrochloride increases from 0.2 to 10 M[8]. For this study, nitric acid was used
instead of hydrochloride to prevent stainless steel substrates from corroding. Also,
deionized water was used to see how dramatic change acidity affects the extraction of
analytes from H2DEH[MDP] PLF.
First, the dependency of plutonium back-extraction on the nitric concentration
was studied by placing PLFs in 3M, 8M, or concentrated nitric acid baths for about 24
hours. Extraction solution was then electrodeposited on a stainless steel substrate for
alpha spectroscopy to quantify the amount of plutonium extracted using nitric acid. The
239Pu back-extraction was ineffective with 3M and 8M nitric acid. The average plutonium
extractions were 9.87±4.18% and 3.93±4.00% for 8M and 3M nitric acid, respectively.
The 239Pu recovery was the highest with concentrated nitric acid. The percent recovery
was over 100% as shown in Table 3-8. The possibility of introducing impurities or
contamination during the sample preparation process was ruled out due to consistent high
recovery in the entire sample population. Also tracers and reagents used in the process
were inspected with mass spectroscopy for presence of plutonium and no significant
239Pu was measured.
The percent recoveries were calculated based on the alpha spectroscopy
measurement. This means that only the PLF surface activity was used to calculate a back-
extraction recovery. A higher than 100% analyte recovery confirms that unaccounted
59
activity discussed in 3.3.1 Analyte Extraction Characterization section is indeed being
deposited on the entire body of the PLF not just on the surface. Based on an assumption
that all unaccounted activity is being deposited on the PLF, percent back-extraction was
adjusted to reflex the unaccounted activity. The adjusted percent recovery for
concentrated nitric acid was well below 100% and percent recoveries for the rest of
reagents are shown in Table 3-8.
Table 3-8 Plutonium back-extraction with nitric acid and DI water
The same experiments were performed with deionized (DI) water to back-extract
plutonium from the PLF. The ligand is normally used in acidic condition and placing it
under DI water has potential to change the characteristic of the ligand. Ultrapure
deionized water used in the experiment was obtained from Barnstead Fi-Stream II Glass
Still purification system. About 50% of the plutonium was removed based on surface
activity measurement, and 19% was extracted based on the entire PLF activity.
Plutonium back-extraction was effective with concentrated nitric acid and DI
water. The activities back-extracted in these experiments were high enough to perform
TIMS. However, a considerable amount of activity was still left on the PLF based on the
unaccounted activity data. It is always advantageous to fully back-extract analyte of
interest from PLF to perform destructive analysis. A problem may arise in the case of an
environmental sample where the total activity available for analysis is in few dpm range,
Reagent Percent recovery based on PLF surface activity (%)
Percent recovery based on unaccounted activity (%)
3M nitric acid 3.93±4.00 N/A 8M nitric acid 9.87±4.18 N/A 16M nitric acid 132.55±20.95 45.64±15.84
DI water 50.03±9.97 19.13±6.26
60
which will require the most analyte to be back-extracted to perform reliable analysis. The
nitric acid or DI water back-extraction method will not provide sufficient activity to
perform TIMS analysis for such a sample.
3.6.2 Back-extraction with Isopropanol
One possible method to increase the recovery of plutonium from PLF substrate is
completely extracting plutonium and ligand complex from the polymer matrix.
H2DEH[MDP] is insoluble in water but soluble in organic diluent [37]. With this
information, PLFs were placed in isopropanol bath to completely remove H2DEH[MDP]-
plutonium complexes from the polystyrene structure. Once PLF was removed from the
bath and isopropanol was completely evaporated, white residue was observed in the
bottom of the beaker. Hydrogen peroxide and sodium vanadate were added to samples to
destroy the plutonium complex. Samples were cleaned with anion column
chromatography then electrodeposited on a stainless steel planchet. The plutonium
recovered with isopropanol was similar to one achieved by the concentrated nitric acid.
Table 3-9 shows percent plutonium recovered by the isopropanol method. PLF surface
based activity recovery calculation showed over 100% recovery, which again confirms
that plutonium had penetrated through the depth of the PLF and deposited under the
surface. The percent plutonium recovery was readjusted based on the PLF surface and
unaccounted activity. The isopropanol back-extraction was less effective than expected.
Since isopropanol would have removed the entire plutonium-ligand bonds from polymer
structure, it was theorized that the low back-extraction was caused due to ineffectiveness
61
in breaking bond between plutonium and ligand. The improvement can be made by
utilizing more aggressive chemical method. However, it would be more time consuming
and complicated than the current procedure. It was decided to focus on establishing TIMS
analysis process for the back-extracted samples since both concentrated nitric acid and
isopropanol methods provide enough plutonium activities to perform mass spectroscopy
analysis.
Table 3-9 Plutonium back-extracted from H2DEH[MDP] PLF using isopropanol
3.6.3 TIMS Analysis
Selected samples from the extraction studies were further analyzed with Thermal
Ionization Mass Spectrometry (TIMS) to investigate feasibility of performing plutonium
isotopic measurements. Four samples from the nitric acid experiment and eight samples
from the isopropanol samples were selected for TIMS analysis. For nitric acid experiment
samples, only 239Pu was added to the samples and 242Pu tracer was used to measure the
yield from the process. 240Pu and 239Pu were used in samples from the isopropanol
experiment. 240/239Pu samples were also traced with 242Pu. The 240/239Pu ratio was
controlled from 4 to 27% as shown in Table 3-10.
Reagent Percent recovery based on PLF surface activity (%)
Percent recovery based on unaccounted activity (%)
Isopropanol 129.60±9.15 32.51±2.11
62
Table 3-10 240/239Pu isotopic ratio for each samples
Sample ID 240/239Pu Ratio (%) Isopropanol-A 4.37 Isopropanol-B Isopropanol-C 8.81 Isopropanol-D Isopropanol-E 17.78 Isopropanol-F Isopropanol-G 26.71 Isopropanol-H
Each sample was cleaned using the Bio-rad AG® MP-1 resin. Samples were
processed with perchloric acid to eliminate any organic matter that may pass through the
resin bed. Samples were electrodeposited on a degassed zone-refined rhenium filament.
These filaments were loaded on a 20 slot sample turret shown in Figure 3-19. Once
samples were loaded on the TIMS system, filament was ramped up to 1450 oC to ionize
plutonium.
All samples analyzed with TIMS had low background and showed that the
procedure was adequate to process PLF samples. Sample cleanup process was effective
in removing any organic and inorganic compounds that may have presented in the
sample.
Figure 3-19 (A) TIMS turret with triple-filament (B) TIMS sample turret in chamber
63
As expected, almost no 240Pu was measured from samples back-extracted by nitric acid.
Samples that were back-extracted with isopropanol all showed presence of both 239Pu and
240Pu. The 240/239Pu ratio measured with TIMS were accurate when compared to the
known values as shown in Figure 3-20.
Figure 3-20 Comparison of TIMS 240/239Pu isotopic ratio measurements from back-extracted samples and known values
TIMS analysis for PLF samples are time consuming process due to the back-
extraction and column chromatography. The entire process takes at least 3 to 4 days to
complete. One way to decrease total analysis time is by directly placing PLF on a TIMS
filament without chemical processing. In the sample preparation, section of the PLF will
be removed from substrate and directly mounted on a filament as shown in Figure 3-21.
This will shorten the total analysis time and at the same time may also provide
enhancement in analyte ionization potential. The thermal ionization efficiency of
plutonium is extremely low. The best reported ionization efficiency for plutonium is 1-
2% [45]. One of way to improve plutonium ionization efficiency is to use additive, such
0
5
10
15
20
25
30
0 1 2 3 4 5
240/
239 P
u ra
tio (%
)
Sample
PLF TIMS
Mass
64
as graphite. The additive increases the work function of the metal filament, which
effectively increases the ionization potential. The work function of carburized rhenium is
about 0.4 eV higher than the pure rhenium [46]. H2DEH[MDP] and polystyrene are
mainly consisted of carbon and hydrogen. With large population of carbon atoms, it is
possible to have ligand and/or polystyrene greatly improve a thermal ionization
efficiency of plutonium.
Figure 3-21 Illustration of PLF direct sample mounting on TIMS filament
With the current PLF design, directly mounting a sample on a TIMS filament is
inadequate due to the possibility of iron residue from stainless steel substrate interfering
with the TIMS signal. So instead of removing PLF from substrate and mounting onto a
filament, two approaches were taken to validate compatibility of ligand and polystyrene
with TIMS analysis. The first approach was coating PLF directly onto the filament, then
stippling the plutonium tracer solution onto the PLF to test the effect of the polystyrene
and ligand on the TIMS signal. This first approach will be called the ligand-polymer
method. The second approach was complexing plutonium with H2DEH[MDP] ligand
then stippling the solution on filament. This approach will be called the ligand complex
65
method. The second method would eliminate polystyrene from the process and only test
H2DEH[MDP] ligand’s role in TIMS process. This was intended as a surrogate samples
to represent isopropanol back-extracted Pu-ligand complex directly deposited on filament
without column chromatography process. The optical microscopic views of the filaments
from the two methods are shown in Figure 3-22.
Figure 3-22 TIMS filament prepared with (A) ligand-polymer method (B) ligand complex method
TIMS filaments for ligand-polymer method were prepared by stippling 1 µl 1:20
H2DEH[MDP] PLF stock solution directly onto a rhenium filament. PLF coatings
solidify and are ready for the use within few hours of stippling. Once the PLF filament
was ready to use, 1 µl of plutonium standard was stippled onto the filament and air dried.
Two plutonium standards were used and information is given in Table 3-11. The ligand
complex method samples were prepared with same plutonium standard as the ligand-
polymer samples. The standard solution was first dried then re-dissolved in 0.01M nitric
acid and H2DEH[MDP]-isopropanol solution. Samples were left for two hours to form
Pu-ligand complexes then transferred onto rhenium filaments. Both type of samples were
run the same way as the standard electrodeposited samples.
66
Table 3-11 Information of plutonium standards used in TIMS analysis Standard 1 Standard 2 Certification agency New Brunswick Laboratory National Institute of
Standard & Technology Certification number CRM 128 SRM 4334G Radionuclides 239Pu and 242Pu 242Pu Atom ratio 0.9993±0.0002 (239Pu/242Pu) NA
TIMS data showed several deficiencies with the new sample preparation methods.
The ligand complex samples did not run well and showed very low counts. Plutonium
isotopic measurement could only made on few samples due to generally low counts.
Plutonium was not effectively transferred to the filament with this technique. Only a few
µl of solution was used to prepare each sample and solution volume seems to be too
small to effectively form ligand-plutonium complexes. This deficiency may be eliminated
by increasing the overall solution volume used to increase change of ligands to form
complexes with analyte. A longer equilibration time with slight agitation could also help
with the formation of complexes.
Figure 3-23 TIMS spectrum from 242Pu sample prepared by ligand-polymer method
67
The ligand-polymer samples consistently showed good and stable signal.
However, the background was consistently high at each mass number as shown in Figure
3-23. This behavior is unexpected and unusual. Normally the background is consistently
high in the entire spectrum and not just at each mass number. This behavior was not
observed with the ligand complex samples, which do not contain polystyrene. Also,
conventional electrodeposited samples did not show any background issue, which means
that plutonium standard was not the issue. These samples were prepared in a clean room
and sample contamination was not the cause of the background. This is a good indication
that polystyrene is causing the background issue during the ionization process.
3.7 H2DEH[MDP] PLF Conclusions
H2DEH[MDP] PLFs were effective in plutonium and uranium extraction. 1:10,
1:15, and 1:20 PLF showed similar plutonium extraction behavior. Since 1:20
H2DEH[MDP] PLF was most cost effective, most experiments were performed with 1:20
PLFs. Close to 50% of plutonium was extracted on the surface of 1:20 PLF with 1M
nitric acid. It is important to point out that H2DEH[MDP] PLFs were consistently
susceptible to plutonium penetrating and depositing below the surface. The internal
radiation within the body of PLF did not cause a noticeable degradation in alpha spectra.
The analyte penetration issue was beneficial in the TIMS analysis. Plutonium was
successfully back-extracted from PLF with DI water, concentrated nitric acid, and
isopropanol. The isopropanol removed H2DEH[MDP]-plutonium complexes from
68
polymer structure and showed best back-extraction ability. TIMS analysis was completed
without any issues and the isotopic measurement was accurate. TIMS analysis for PLF
samples are time consuming process due to back-extraction and column chromatography.
The entire process takes least 3 to 4 days to complete. One way to shorten the time was to
directly mounting PLF onto the filament. Preliminary studies showed that direct
mounting has great potential to be utilized in TIMS analysis. Further studies are required
to fine tune the method to be effective.
H2DEH[MDP] PLF showed consistency similar to the electrodeposited samples.
The overall analyte recovery was lower than electrodeposited samples. However, PLF is
designed to be a rapid field deployable screening technique and consistency is more
important than the recovery. H2DEH[MDP] PLFs were also tested with unknown activity
samples and confirmed that the PLF system can be effectively used to process unknown
samples.
H2DEH[MDP] PLF was capable of co-extracting or selectively extracting
plutonium over uranium depending on the PLF composition. With 1:5 PLF, about 23% of
plutonium and 20% uranium were simultaneously extracted with 1M nitric acid. 1:10 and
1:20 PLFs preferably extracted plutonium over uranium with 1M nitric acid. The uranium
alpha spectra peaks were well separated from plutonium peaks, and it was possible to
perform isotopic measurements.
69
4. Chapter 4
Di(2-ethylhexyl) phosphoric acid (HDEHP)
4.1 Introduction
Di(2-ethyl hexyl) phosphoric acid (HDEHP) ligand based PLF were studied for
plutonium and uranium extraction in various conditions. Samples prepared in the
experiment were examined using alpha spectroscopy and thermal ionization mass
spectroscopy (TIMS) to measure analyte content in the PLF. Digital autoradiography
technique was also used to study distribution of plutonium on the PLF surface. PLFs
were effective in plutonium extraction but generally ineffective for uranium in conditions
tested.
4.2 Theory and Background
HDEHP is an effective metal extractant. It has very efficient chelating properties
for a wide variety of metal ions. HDEHP is an amphiphillic molecule with two long
hydrocarbon chains and a polar end with a phosphoryl oxygen (P=O) and an acidic –OH
group as shown in Figure 4-1 [47].
Figure 4-1 Chemical structure of HDEHP
70
HDEHP can be easily synthesized by reacting phosphorus pentoxide with 2-ethylhexanol
to produce a mixture of mono, di, and tri phosphates. Di(2-ethyl hexyl) phosphoric acid is
isolated from the rest of the phosphates based on solubility. The solubility in water is
highest for mono and lowest for tri phosphates. The order of solubility is opposite for
nonpolar solvents [48].
4𝐶8𝐻17𝑂𝐻 + 𝑃4𝑂10 → 2[(𝐶8𝐻17𝑂)𝑃𝑂(𝑂𝐻)]2𝑂
[(𝐶8𝐻17𝑂)𝑃𝑂(𝑂𝐻)]2𝑂 + 𝐶8𝐻17𝑂𝐻 → (𝐶8𝐻17𝑂)2𝑃𝑂(𝑂𝐻) + (𝐶8𝐻17𝑂)𝑃𝑂(𝑂𝐻)2
HDEHP has two metal extraction mechanisms. The first mechanism involves an
ion-exchange between H+ and metal ions. In this process, HDEHP loses the H+ ion and
form a conjugate base. A sufficient number of these extractant anions come together to
form a complex with a metal cation [49]. This process is a dominating extraction
mechanism at the low acidity condition [50]. The second mechanism utilizes a
phosphoryl oxygen group to form a complex with the metal cation. The P=O group has a
strong electron donor and it is in a sterically favorable position to form a metal complex
[49]. This P=O extracting mechanism is the main process to extract metal in the high
acidity condition [50].
HDEHP has shown effectiveness in extracting lanthanides, selective actinides,
and other trivalent elements [49]. Several authors have reported that lanthanides and
elements with +3 oxidation state have similar extraction behavior in nitric acid [50]–[52].
The distribution ratio for lanthanides rapidly decreases at lower nitric concentration then
71
start to increase at higher concentration as shown in Figure 4-2 [50], [51]. The trivalent
americium, curium, and yttrium exhibit similar trend as trivalent lanthanides [53]. This
extraction trend can be also observed from hydrogen chloride solution [54]. The
distribution ratio plot shown in Figure 3-1 was generated based on Svantesson’s
empirical equations, which shows good agreement with experimental data [50].
Plutonium and uranium distribution ratios are less dependent on the nitric
molarity than trivalent elements. The dependency is linear with negative slope as shown
in Figure 4-2. For plutonium, it had been reported that HDEHP has high affinity to both
trivalent and pentavalent plutonium [55].
Neptunium extraction by HDEHP has a unique dependency on nitric acid
concentration. The behavior is believed to be a result of neptunium oxidation state change
due to the change in solution acidity. Np(IV) and Np(VI) have very high affinity to
HDEHP. However, Np(V) has low extractability by HDEHP. Pentavalent neptunium is a
dominating specie in a high acidity solution. As the acidity of the solution decreases,
Np(V) is converted to Np(IV) and Np(VI), which in turn leads the distribution ratio to
increase rapidly.
72
Figure 4-2 HDEHP distribution ratio dependency on HNO3 concentration for various ions [50]
4.3 Plutonium and Uranium Extraction
HDEHP PLF analyte extraction behavior was tested over various conditions. The
set of experiments performed for HDEHP PLF was similar to H2DEH[MDP] based PLF.
The analyte extraction by HDEHP is well known in liquid/liquid and in resin bead
extraction condition. However, there is a great possibility that extraction behavior is
completely different for the PLF form. In case of H2DEH[MDP] based PLF (which was
73
examined in Chapter 3) the PLF analyte extraction behavior is noticeably different from
one observed from liquid/liquid or resin bead based extraction.
4.3.1 Analyte Extraction Characterization
Four different composition HDEHP PLFs – 1:2, 1:5, 1:10, and 1:20 – were
prepared and tested for plutonium extraction over 0.01 to 8M nitric acid solution to
establish the baseline behavior. Different ratio PLFs showed significantly difference in
color as shown in Figure 4-3. 1:10 and 1:20 were both clear with no visual difference
between two. 1:5 PLF was mostly clear but it had opaque colored spot. The entire surface
of 1:2 PLF was opaque in color and it was noticeably soft compare to other ratio PLFs.
1:2 PLF visibly had rough surface and it was easily damaged during sample handling.
239Pu solutions used in this study were prepared with 0.01, 0.1, 1, or 8M nitric acid
solution. The PLF testing procedure was same as the procedure used for H2DEH[MDP]
PLF. 2.5 to 3mL of nitric acid concentration adjusted 239Pu tracer was stippled on the
PLF surface and equilibrate time of 3 hours were used.
Figure 4-3 HDEHP ligand based PLFs
The plutonium recovery by HDEHP PLF was dependent on both nitric acid
concentration and ligand to polymer ratio. 1:2 PLF consistently had the highest recovery
74
in nitric concentration examined in this experiment followed by 1:5 as shown in Figure
4-4. It should be noted that spectra from 1:2 ratio PLFs consistently had long tailing and
the ROI for the plutonium peak had to be increased to encompass total counts from the
tracer. 1:10 and 1:20 PLFs had close to zero percent recovery in all nitric acid
concentration except for 0.01M. The highest plutonium recovery was observed in 0.1M
nitric acid for both 1:2 and 1:5 ratio PLFs.
Figure 4-4 The baseline performance of HDEHP PLF in plutonium extraction as a function of nitric acid concentration
The alpha spectrum resolution was quantified by measuring Full Width at Half of
the Maximum (FWHM) using Bortels’ equation. The tailing component of the peak was
also measured along with FWHM. The tailing term combined with the resolution
represented the total broadness of a peak. The peak resolutions and tailing measurements
for 0.1M nitric acid solution samples are given in Table 4-1.
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
0.01 0.1 1 10
Reco
very
(%)
Nitric Acid (M)
1:2
1:5
1:10
1:20
75
Table 4-1 Alpha spectra resolutions and tailing terms for HDEHP PLFs PLF ratio FWHM (keV) Tailing 1:2 7.85±2.95 305.19±5.84 1:5 15.86±0.67 18.65±0.51 1:10 12.37±2.43 22.10±2.40 1:20 12.74±1.62 24.72±1.48
At a glance, the data from Table 4-1 seems to indicate that the 1:2 ratio PLF
sample has the best resolution among the HDEHP PLFs. However, it is important to note
that the spectrum of 1:2 PLF was not conforming to the typical alpha spectrum. The
Bortels’ equation was not designed for such an uncommon peak shape, and there was
large uncertainty in the peak fitting. Also, it must be noted that the tailing term from an
alpha spectrum is as important as the resolution in analyzing the spectrum. The tailing
term for 1:2 is extremely large compared to other PLFs as shown in Figure 4-5. This
indicates that alpha spectrum from 1:2 ratio PLF is too broad to be effectively used in any
meaningful analysis. A large tailing term from 1:2 PLF is a possible indication that large
amount of ligands present in the film reduced the smoothness of the surface as compared
to the other PLFs. A rough surface is known to cause source attenuation in an alpha
source, which leads to degradation in spectrum. Also, it can be noted that the 1:2 ratio
PLF surface was not as rigid as the other ratio PLFs, and it was prone to scratching
during sample handing. The resolutions and tailing terms for the other three PLFs were
similar to each other and comparable to the electrodeposited alpha sources. This is a good
indication that the source attenuation in 1:5, 1:10, and 1:20 PLFs are minimal and
suitable for alpha spectroscopy.
76
Figure 4-5 Alpha spectra for 1:2 (blue) and 1:5 (red) PLFs
Based on the alpha spectroscopy resolution and recovery, 1:5 HDEHP PLF was
the best candidate to be used in plutonium separation from 0.1M nitric acid. The main
reason that different ratio PLFs provided different recovery is due to the number of active
sites available on the surface for plutonium. The active sites were less on 1:10 and 1:20
PLFs than either 1:2 or 1:5 PLFs, and plutonium recovery was expected to be affected by
the amount of ligand in PLF. However, it was not expected to see significantly drop off in
plutonium recovery from 1:5 PLFs to 1:10 and 1:20. All four PLFs examined should have
provided enough ligands to extract plutonium from the solution. Based on the plutonium
extraction behavior, it was theorized that there is some kind of interaction between ligand
and polystyrene that cause the orientation of ligands to change based on ligand to
polymer ratio. The orientation of ligands in 1:2 and 1:5 ratio PLFs are clearly more
favorable for plutonium extraction than in 1:10 and 1:20 ratio PLFs. Another possible
exploration of such an extraction behavior is that the low amount of ligand in the
77
polystyrene may have caused most of the ligands to be entangled in the bulk polymer
structure and only a trace amount to be present on the surface for the extraction.
Since the first experiment was coarse with range gap between the data points, a
more detailed experimentation was carried out based on the initial data. PLFs were
prepared with small ratio increments over and under the 1:5 PLF and tested for plutonium
extraction. Total of four new PLF compositions were prepared: 1:3, 1:4, 1:6, and 1:7.
These ratios were selected to provide finer detail between 1:2 and 1:5 and between 1:5
and 1:10 to see whether the change in plutonium extraction is a sudden or gradual
change.
1:6 and 1:7 PLFs showed slight improvement in plutonium extraction over 1:10 or
1:20 PLF in all nitric acid concentration as shown in Figure 4-6. The plutonium
recoveries were still low, below 10%, even with increase in HDEHP ligand in PLF. Both
1:3 and 1:4 PLFs had similar spectrum tailing issue observed in 1:2 PLF. Alpha spectrum
ROI was adjusted accordingly to encompass entire counts from 239Pu. The long peak
tailing is undesirable in alpha analysis due to possible peak convolution caused by the
tail. For the case of 1:3 and 1:4 PLFs plutonium recoveries generally fall between 1:2 and
1:5 in all nitric acid concentration except for 0.1M as shown in Figure 4-7. In 0.1M nitric
acid, 1:5 still had higher plutonium recovery than either 1:3 or 1:4 PLF.
78
Figure 4-6 Plutonium recovery by 1:6 through 1:20 HDEHP PLF as a function of nitric acid concentration
Figure 4-7 Plutonium recovery by 1:2 through 1:5 HDEHP PLF as a function of nitric acid concentration
The plutonium recoveries were plotted as function of PLF ratio in Figure 4-8 to
better show the recovery transition as the function of PLF ratio. There were sudden
plutonium recovery efficiency change from 1:6 and 1:5 PLF. It seems to be that 1:5 is a
transitioning point from low to high recovery. This greatly suggests that ligands have to
reach a certain mass compared to polymer to become available for analyte extraction. The
0.00
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79
behaviors were similar for all three nitric acid concentrations shown in Figure 4-8. In
0.01M and 1M nitric acid, percent plutonium recovery reached a plateau at between 1:3
and 1:4 before achieving highest plutonium recovery with 1:2 PLF. In 0.1M nitric acid,
however, plutonium recovery spiked at 1:5 PLF then significantly decreased at 1:4 PLF.
Plutonium recoveries then start to linearly increase from 1:4 to 1:2 PLF.
The 1:5 PLFs consistently had large standard deviations with 0.1M nitric acid.
The standard deviation could be result of a number of different issues. The first
possibility is due to inconsistency in PLF composition. The 1:5 PLF is right at the
transition point and slight change in ratio may dramatically change the plutonium
recovery. The second possibility is due to inconsistent plutonium states in the tracer
solution used in the experiment. Plutonium oxidation state issue was already discussed in
Chapter 3.
Figure 4-8 Plutonium recovery by HDEHP PLF as function of PLF composition
80
Some of the PLFs were also tested for penetration of plutonium through the depth of the
polymer film. It has been shown in H2DEH[MDP] PLF that plutonium was capable of
penetrating and depositing below the surface. Tracer solutions that were left on PLF were
collected and electrodeposited to measure any unaccounted plutonium activity. The
unaccounted plutonium activities shown in Figure 4-9 indicate that plutonium had
potentially deposited through the body of PLF.
Figure 4-9 Unaccounted plutonium by H2DEH[MDP] PLF as function of nitric acid concentration
4.3.2 Analyte Extraction Time Dependency
An analyte extraction time study was performed with 1:5 HDEHP PLFs and 0.1M
nitric acid solution. PLFs were tested with exposure time from 10 to 180 minutes. The
extraction conditions were kept consistent throughout the experiment except for the
exposure time. The plutonium recovery linearly increased from 10 to 60 minute exposure
time then slightly dipped for 90 and 120 minute exposure before the maximum recovery
was achieved at 180 minutes. Recoveries from 60 to 120 minutes were, however, all
0
10
20
30
40
50
60
0.01 0.1 1 10
Pu re
cove
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)
Nitric concentration [M]
1:3
1:4
1:5
1:6
1:7
1:10
1:20
81
within standard deviation of measurements. The HDEHP PLF analyte extraction
dependency on time was similar to one observed with 1:20 H2DEH[MDP] PLF. The
plutonium recovery by HDEHP and H2DEH[MDP] PLFs function of exposure time is
plotted in Figure 4-10. Student’s t-test was performed to confirm and assess the statistic
difference between plutonium recoveries between 60 to 180 minutes. The recoveries
measured at 60 and 120 minute exposure time were statistically indifferent from the 180
minute measurement at 95% confidence level. However, 90 minute plutonium recovery
was statistically different than 120 minute recovery based on student’s t-test.
Figure 4-10 HDEHP and H2DEH[MDP] PLF plutonium recoveries at different exposure time
The plutonium recovery dependency shown in this study provides flexibility in
deploying this technique in emergency response. Based on the sample type, the
equilibration time can be changed to best suit the particular sample. For example,
samples with high activity can be rapidly processed since HDEHP PLF was capable of
extracting 10% of plutonium from nitric acid even at 10 minutes. Depending on the initial
0
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50
60
70
0 30 60 90 120 150 180
Pu re
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)
Time (min) HDEHP H2DEH[MDP]
82
sample activity, 10% recovery may provide enough activity for alpha spectroscopy. Even
for the sample with low activity, a 10 minute exposure time would most likely provide
enough activity for mass spectroscopy analysis. As mentioned before in Chapter 3, about
100 femtogram of plutonium is needed for reliable TIMS analysis. In any conceivable
post-detonation situation, the mass of plutonium in the sample collected near the ground
zero will be significantly higher than 100 femtogram.
4.3.3 Consistency Study
The consistency of HDEHP PLFs was examined by preparing and testing two
batches of 1:5 PLF with 0.1M nitric acid solution. The data from the previous
experiments showed a large standard deviation from 1:5 PLFs that were tested with 0.1M
tracer solution. This high deviation could have been a result of either PLF variation or
oxidation state difference in solutions used. In this experiment, a single plutonium tracer
solution was used for both batches to eliminate possibility of plutonium oxidation states
playing role in extraction behavior. This ensured that any plutonium recovery variation
would be caused by the variation in PLF itself.
Stock solutions were prepared on different dates and PLFs were also synthesized
on different dates. The amounts of each PLF component used in the stock solutions are
listed in Table 4-2. The weight ratio between ligand and overall mass was kept as close as
possible to minimize difference in two PLF batches. PLFs from both batches were
prepared with solvent cast method. Once PLFs were prepared and ready for the
experiment, the appearance of both batches was compared. The first batch was more
83
opaque and second batch was mostly clear with small opaque spot. As shown in Table
4-2, difference between PLF compositions was minimal. The small difference in
composition of these PLFs is not great enough to explain the discrepancy.
Table 4-2 Mass of components used to prepare two HDEHP PLF batches for consistency study Batch 1 Batch 2 HDEHP (g) 1.402 1.423 Polystyrene (g) 5.589 5.647 THF (g) 28.119 28.954
Two batches and these stock solutions were prepared on different dates. The major
difference between two batches was the time spent on outgassing THF from the polymer
structure. Both stock solutions were left to dissolve polystyrene for 3 days before
preparing PLF. The first batch was out gassed for 30 days before using in the study
compared to only 2 days for the second batch.
PLFs were tested to check whether the physical appearance has any effect on the
plutonium recovery. Six PLFs were selected from each batch and tested on same date
using freshly prepared 239Pu tracer in 0.1M nitric acid. The experiment condition was
same for both batches. Each sample was counted in six different alpha counters for two
reasons. First, it was to ensure fidelity of PLF in multiple sample counting. Second, it
was performed to measure activity variation introduce by the different counting systems.
Since radiation decay is a stochastic process, there will be slight difference in activity
each time sample is counted. The activity variation due to the counter should be minimal
and lower than variation caused by PLF itself.
Plutonium recoveries were significantly different between the batches. PLFs from
first batch had consistently higher recoveries than the PLFs from second batch. The entire
84
count data is plotted in Figure 4-11 and mean plutonium recovery from each batch is
shown in Table 4-3.
Figure 4-11 Plutonium recoveries by 1:5 HDEHP PLFs with 0.1M nitric acid solution
The average plutonium recovery from first batch was about three times higher than the
one from second batch. As mentioned before, a small difference in composition of these
PLFs is not great enough to explain for the discrepancy. More plausible explanation
would be that the recovery discrepancy would have been due to an entrapment of THF in
polymer structure. The possibility of THF entrapment was discussed in Chapter 2 and it
is possible that a large amount of THF was still remaining in PLFs from the second batch.
Table 4-3 Average plutonium recovery by HDEHP PLF batches First Batch Second Batch Overall Detector 1 32.28±5.39% 11.08±5.05% 19.03±11.03% Detector 2 30.51±5.43% 9.98±4.86% 18.73±11.07% Detector 3 32.64±6.20% 10.58±4.66% 20.04±11.98% Detector 4 30.12±4.82% 9.68±4.31% 18.47±10.92% Detector 5 31.22±5.44% 9.62±4.51% 18.82±11.45% Detector 6 32.39±4.93% 9.75±4.08% 19.40±11.72%
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0 1 2 3 4 5 6 7 8 9 10 11 12 13
Plut
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Sample #
Detector1
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Detector3
Detector4
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Detector6First Set Second Set
85
It is theorized that the difference in the color for both batches were caused by
unevaporated THF. Also, the color of second batch PLFs changed after counting under
the vacuum condition. There was no noticeable difference in two batches in appearance
as shown in Figure 4-12. Placing samples under the vacuum may have evaporated the
THF out of the polymer structure. The effect of THF on the analyte recovery mechanism
was not fully understood but it is the most likely cause of the low analyte recovery in
second batch.
Figure 4-12 Comparison of two HDEHP PLF batches after alpha counting
The effect of THF in analyte recovery was studied by further testing PLFs from
the second batch. The focus of this experiment was to remove THF from PLF matrix then
test PLF for plutonium extraction to quantify effect of THF on the recovery. PLFs from
second batch were left on bench top to further outgas the solvent from the polymer
matrix. After 16 days of outgassing, which was 13 days longer than PLFs used in
consistency experiment, six PLFs were selected for the experiment. All six PLFs were
opaque and similar to first batch PLFs tested for plutonium extraction. These PLFs were
divided into two groups: the first group was heat treated by placing it in a furnace for an
hour to boil the THF out of the polymer and the second group was used without further
First Set Second Set
86
processing. PLFs from two groups showed significant visual difference as shown in
Figure 4-13. PLFs that were heat treated became clear with no opaque spots. Whereas
unprocessed PLF was just opaque.
Figure 4-13 1:5 HDEHP PLF (A) after heat treatment (B) after 16 day outgassing
PLFs were tested with the standard plutonium extraction procedure. Each sample was
counted once and data was compared with the data from the consistency study. Both heat
treated and outgassed PLFs showed great improvement in plutonium recovery over the
second batch PLFs. The heat treated PLFs, however, showed long peak tailing in its alpha
spectrum. The ROI in the counting software was increased accordingly to account for the
long tailing. The tailing indicated that THF had damaged the surface while evaporating
and caused self-absorption on the surface. The spectra are plotted in Figure 4-14 to
compare the resolution and tailing.
Table 4-4 Plutonium recovery improvement after outgassing and heat treatment Heat Treated Air Dried First Batch* Second Batch* 32.27±3.10% 27.16±7.40% 31.53±5.08% 10.11±4.28%
*Average plutonium recovery was calculated using data from all six detectors
The improvement in plutonium recovery is a good indication that THF plays a role in
analyte recovery. It is essential to effectively remove THF from PLF. The best approach
to the THF issue is to air dry PLF for longer duration. Plutonium recovery was improved
87
by air drying PLF for 13 extra days without any adversary effect on spectrum resolution.
Thermally evaporating THF showed greater improvement in plutonium recovery;
however, thermal process introduced source attenuation in sample spectrum.
Figure 4-14 Alpha spectra comparison between heat treated HDEHP PLF (blue) and air dried PLF (red)
It is important to further discuss the color difference observed from 1:5 HDEHP
PLFs used in the experiment. The color difference between first and second batch PLFs
was believed to be a result of the different length time used to outgas THF from the PLFs.
A PLF was closely observed over 12 day period after the preparation to record the
changes in color. The PLF was mostly clear initially with some white spots. The gradual
change was, however, obvious as time goes on as shown in Figure 4-15. By the 9th day
after preparing PLF, entire surface became opaque without any clear portion. There was
no change in PLF observed after 9th day. It is believed that after 9 days of outgassing,
PLF is stabilized and no further unforced evaporation of THF is occurring.
0
50
100
150
200
250
300
4800 4850 4900 4950 5000 5050 5100 5150 5200
Coun
ts
Energy (keV)
Resurfaced
Outgassed
88
Figure 4-15 1:5 HDEHP PLF surface color progression over 12 days
The heat treatment of PLF also has shown to cause change in PLF color as shown in
Figure 4-16. The color change in heat treated PLF was more carefully studied by
monitoring PLF over 12 days after the heat treatment. The heat treated PLF becomes
clear initially then within few hours start to develop opaque sports. The opaque spot was
only developing along the edge for first day then spots started to appear at the center of
PLF. Figure 4-16 is showing the progression of spots developing on the PLF. By the 12th
day after the heat treatment, entire surface started to show white tint.
89
Figure 4-16 Heat treated 1:5 HDEHP PLF surface color progression over 12 days
4.3.4 Alternate PLFs
The 1:5 HDEHP PLFs prepared by spin coating method were tested for plutonium
extraction. The 1:5 PLFs were totally clear without any white spots, which is a clear
difference from the solvent casted PLFs. The spin coating removed any excess PLF
solution and only about 12 mg of material was coated on the stainless steel substrate.
PLFs were tested for plutonium extraction with the standard method to compare against
solvent cast PLF. The plutonium recovery on the PLF surface was lower than one
achieved with the solvent casted PLF. Only 19% of plutonium was recovered compared
to 49% with solvent casted PLF. The main issue with the spin coated PLFs was the
tailing in the alpha spectrum, which indicates sample attenuation. Figure 4-17 is a
comparison of spectra from solvent casted PLF and spin coated PLF. The spectrum from
spin coating clearly showed a longer left hand tailing than the solvent casted PLF.
90
Figure 4-17 Alpha spectra comparison between for heat treated 1:5 HDEHP and regular PLFs
The degradation of alpha spectrum is likely to be a result of the thin profile of the film.
Plutonium was deposited on both the surface and the body of the PLF. The alpha decay
energies from plutonium that deposited in the body of PLF were losing energy as it
escaped the PLF.
The spray coated HDEHP PLFs were not examined for plutonium extraction.
Spray coated PLFs had rougher surfaces and normally suffer from resolution degradation
issue based on H2DEH[MDP] data from Chapter 2. The degradation issue worsen with
the spray coating method and this method will not provide any advantage over solvent
casting or spin coating method to warranty any further investigation.
4.4 Surface Characterization
The surface characterizations of HDEHP PLFs were performed with Scanning
Electron Microscope (SEM) and digital autoradiography. All the surface characterization
studies were performed with the solvent casted PLFs. SEM was used to see any
91
microscopic defects on the PLF surface, and digital autoradiography was used to image
the distribution of plutonium. SEM analysis revealed presence of defects on all PLF
samples examined as shown in Figure 4-18. Images were taken at different
magnifications to show the types of defects that were presented on the PLF surfaces.
Thus, a direct comparison could not be made. The origin of these defects could not be
explicitly determined, but some of the defects appeared to be generated during sample
handling. As mentioned before, the 1:2 ratio PLF surface was not rigid and was prone to
scratching during handling. Types of defects observed in the 1:2 PLF resemble scratches
that may have been created after the film was formed. Based on the alpha spectroscopy
data, it seemed that the surface defects played no major role in plutonium recovery.
Figure 4-18 SEM images for different ratio HDEHP PLFs
92
Radiography images of samples were collected to study the plutonium distribution
on the PLF surface. 1:2 and 1:5 PLFs were used in the plutonium distribution study. The
digital radiography image in Figure 4-19 shows that the distribution was not uniform on
the PLF surface. There seems to be hot spots along the edges and in the center of the
samples. The digital autoradiography image shown in Figure 4-19 was imported and
analyzed with the particle distribution software. Six samples were all processed and it all
showed uneven distribution as shown in Figure 4-20 and Appendix C. The location of hot
spots were unique to each sample but it was confirmed to be mostly along the edge and in
center of PLF by the particle distribution software. The analyte distributions trend was
indifferent between two PLF compositions examined.
Figure 4-19 Digital autoradiography image of 1:2 and 1:5 HDEHP PLFs
The plutonium distribution on HDEHP PLFs were different than ones observed
with H2DEH[MDP] PLFs. Hot spots along the edge was unique to HDEHP PLFs. Since
ligand is the only component within the PLF that had shown any affinity to plutonium,
the particle location map can be interpreted as a ligand locational map. Conglomeration
of HDEHP along the edge would most likely have happened during the PLF preparation
1:2
1:5
93
process. Another possible explanation of the highly localized distribution is that defects
on the surface were increasing the overall size of area available for the analytes. HDEHP
ligands were not only on the surface but on the entire body of PLF. The defects or
damages on the surface are exposing ligands that would have normally been below the
surface. Once the ligand is exposed, it has a higher chance of extracting an analyte and
the location is captured on the digital autoradiography image.
Figure 4-20 Plutonium distribution map of HDEHP PLF generated from digital autoradiography image
4.5 Uranium Analysis
HDEHP ligand also has a high distribution ratio for uranium. HDEHP PLFs tested
for uranium extraction with the standard extraction procedure. The only modification to
the procedure was to the tracer solution; natural uranium was used as the tracer instead of
239Pu. 1:2 PLF was excluded from uranium study due to the sample attenuation issue
observed from plutonium samples. The uranium extraction with HDEHP PLF was
ineffective in all condition tested as shown in Figure 4-21. The maximum uranium
recovery was only slightly higher than 4%. The ineffectiveness for uranium extraction
shown by HDEHP is most likely due to the polymer support structure. The polymer used
94
in PLF has no direct affinity to plutonium or uranium; however, it is clearly affecting the
analyte extraction behavior of the ligand. In PLF, ligands were immobilized by the
polystyrene and that had great effect on the analyte extraction behavior.
Figure 4-21 Uranium recovery by HDEHP PLF as function of nitric acid concentration
4.6 Mass Spectroscopy Analysis
A mass spectroscopy experiment was performed in two parts. First back-
extraction of analyte from PLF was studied then possibility of performing TIMS analysis
on back-extracted samples was studied. The main goal of TIMS analysis on PLF sample
was to gain plutonium isotopic information.
-1
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6
0.01 0.1 1 10
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95
4.6.1 Back-extraction with Nitric Acid and Deionized Water
Plutonium back-extraction was first studied with nitric acid and deionized water. HDEHP
ligand showed plutonium extraction dependency on the acidity of the solution. At higher
nitric concentration, HDEHP becomes ineffective for plutonium extraction as shown in
4.3.1 Analyte Extraction Characterization section. Based on this information, 3M, 8M,
and concentrated nitric acid were first examined for the plutonium back-extraction.
HDEHP PLF was individually placed on a 10 mL nitric acid solution bath for 24 hours.
Samples were cleaned using the anion column chromatography then electrodeposited on
stainless steel substrates. These samples were counted with 450 mm2 alpha detectors for
24 hours.
Table 4-5 HDEHP PLF plutonium back-extraction with nitric acid and DI water
Plutonium back-extraction became more effective as the nitric acid concentration
increased. Table 4-5 shows plutonium recovered from PLF with the back-extraction
procedure. The back-extraction trend followed the data collected from PLF experiment
and HDEHP distribution data [17]. In previous data, the ligand becomes less effective in
containing plutonium as nitric acid concentration increases, which was clearly shown in
the nitric acid back-extraction study. The maximum percent back-extraction was higher
than 100% with 16M nitric acid. This is a clear indication that, at least, some of
unaccounted plutonium activity was actually deposited below the surface of HDEHP
Reagent Percent recovery based on PLF surface activity (%)
Percent recovery based on unaccounted activity (%)
3M nitric acid 32.47±4.89 13.96±3.17 8M nitric acid 79.39±12.84 40.85±5.57 16M nitric acid 147.98±13.48 74.25±11.63 DI water 22.31±4.61 8.40±3.82
96
PLF. The percent back-extraction calculated based on unaccounted activity was around
74%, which was more reasonable than the percent recovery based on PLF surface
activity.
Deionized (DI) water was also used in same bases of nitric acid. The ligand is
normally used in acidic condition and placing it under DI water has potential to break
ligand to plutonium bonds. The procedure was the same as the nitric acid procedure
except a reagent was changed from nitric acid to DI water. The percent back-extracted
plutonium data is shown in Table 4-5. DI water was not effective in plutonium back-
extraction and higher concentration nitric acid is a better candidate to extract plutonium
from HDEHP PLF.
4.6.2 Back-extraction with Isopropanol
Plutonium back-extraction was effective with concentrated nitric acid. However,
about 30% of plutonium activity were still left on the PLF based on the unaccounted
activity data. It is always advantageous to fully back-extract analyte from PLF to perform
TIMS or any other destructive analyses. One possible method to increase the recovery of
plutonium from PLF substrate is completely extracting plutonium and ligand complex
from the polymer matrix by placing PLF in organic diluent. The organic solvent back-
extraction was successfully performed with H2DEH[MDP] PLF and showed great
improvement in plutonium recovery over nitric acid or DI water methods.
HDEHP PLFs were individually placed in 10 mL isopropanol bath for 24 hours.
Isopropanol was completely evaporated under the fume hood after removing PLF from
97
the bath. Hydrogen peroxide and sodium vanadate were used to destroy the ligand-
plutonium complexes. For the final step, samples were cleaned using the anion column
chromatography.
Table 4-6 HDEHP PLF plutonium back-extraction with isopropanol
The plutonium back-extraction with isopropanol was less effective than with the
concentrated nitric acid. The percent plutonium back-extracted from PLF is shown in
Table 4-6. The percent back-extraction was about 40% lower than the one achieved with
the concentrated nitric acid. The back-extraction procedure with isopropanol was more
cumbersome and time consuming than the nitric acid procedure. Since ligand-plutonium
complexes were extracted from PLF, extra steps were needed to break the bond and
samples clean up needed larger column bed size than nitric acid procedure. The
isopropanol would have removed the entire plutonium from the PLF. However, the extra
chemical procedure to break complex bonds is causing the lower plutonium recovery than
the nitric acid method.
4.6.3 TIMS Analysis
PLF samples were prepared with 239Pu and then back-extracted with concentrated
nitric acid. Once analyte was back-extracted from PLF, samples were traced with 242Pu to
measure the yield from the process. The cleanup and TIMS procedure developed with
H2DEH[MDP] PLF was also used to process HDEHP samples. Each sample was cleaned
Reagent Percent recovery based on PLF surface activity (%)
Percent recovery based on unaccounted activity (%)
Isopropanol 83.73±14.41 41.99±20.56
98
using the Bio-rad AG® MP-1 resin. Samples were processed with perchloric acid to
eliminate any organic contaminants. Samples were electrodeposited on rhenium
filaments. The cleanup process was effective and all samples analyzed with TIMS had
low background.
Figure 4-22 Comparison of TIMS 239/240Pu isotopic ratio measurements from back-extracted samples and known values
The plutonium isotopic measurements from alpha spectroscopy and TIMS were
compared and plotted in Figure 4-22. Due to the alpha decay energy difference between
239Pu and 242Pu, isotopic ratios were easily calculated from the alpha measurement. The
plutonium isotopic measurements from both techniques were within the standard
deviation of each other. The isotopic ratios measured with alpha spectroscopy had larger
uncertainties compared to TIMS data. The mass spectroscopy measurement uncertainties
were mostly less than 1%.
0
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0.06
0.08
0.1
0.12
0.14
0 2 4 6 8 10
239/
242 P
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Alpha spec
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99
4.7 HDEHP PLF Analysis Conclusions
HDEHP PLFs were effective in plutonium extraction. 1:5 PLF showed best
combination of plutonium extraction and alpha spectrum resolution from eight different
PLF composition tested. The percent plutonium recovery was slightly lower than 50%. It
is important to point out that HDEHP PLF was also susceptible to plutonium penetrating
and depositing below the surface. The 50% analyte recovery was only based on surface
plutonium activity measured by silicon alpha spectroscopy. The overall plutonium
extracted by the entire body of PLF is estimated to be 80%. The internal radiation within
the body of PLF did not cause noticeable sample attenuation in 1:5 PLF. The analyte
penetration issue could be beneficial in destructive analyses. The extra plutonium
contained in PLF body will give more latitude in the analysis. Plutonium was
successfully back-extracted using concentrated nitric acid and TIMS analysis was
performed. TIMS analysis was completed without any issues and isotopic measurement
was accurate.
HDEHP PLF was surprisingly ineffective for uranium extraction from nitric acid.
PLFs tested with natural uranium tracer showed no significant uranium recovery from
0.01 to 8M nitric acid concentrations. HDEHP ligand is actually effective for both
plutonium and uranium in liquid/liquid and resin bead based extraction. It is believed that
polystyrene structure is causing ligand to behave differently than in other matrixes.
One of the main deficiencies observed from 1:5 HDEHP PLFs was inconsistency
in plutonium recovery shown from different PLF batches. The PLF performance was
greatly affected by the THF encapsulated within the PLF body. The plutonium recovery
100
can be successfully increased by air drying THF for longer duration. The thermal
treatment of PLF ensure complete removal of THF, but caused higher surface attenuation,
which caused peak tailing in alpha spectrum.
101
5. Chapter 5
Other Ligands
Trialkyl methylammonium chloride (Aliquat-336), 4,4’,(5’)-di-(tert-
butylcyclohexano)-18-crown-6, and 2-ethylhexyl 2-ethylhexylphosphonic acid
(HEH[EHP]) were also studied for analyte extraction in PLF form. All three ligands were
studied for plutonium extraction and 18-crown-6 was also studied for strontium
extraction. These ligands were less effective than H2DEH[MDP] and HDEHP in analyte
extraction. Aliquat-336 and 4,4’,(5’)-di-(tert-butylcyclohexano)-18-crown-6 also showed
inability to withstand high concentration nitric acid.
5.1 Trialkyl methylammonium chloride (Aliquat-336)
Trialkyl methylammonium chloride, also known as Aliquat-336, is a quaternary
ammonium salt widely used for metal extraction. Aliquat-336 mainly contains octyl and
decyl groups with octyl predominating [56]. It is a clear and extremely viscous liquid
with an average molecular weight of 475 [57]. The chemical structure of Aliquat-366 is
shown in Figure 5-1.
Figure 5-1 Chemical structure of Aliquat-336
102
Aliquat-336 is reported to aggregate and form micelles in inert diluents and the
aggregation can be reduced by using aromatic diluents or by adding a strong Lewis base
[58], [59]. Aggregates behave like monofunctional species in extraction of metal complex
[60]. The extractions are performed in two mechanisms. Anionic species are extracted as
ion pairs and neutral species are extracted as adducts [59], [61].
Aliquat-336 in resin bead form is an extremely effective extractant for tetravalent
actinides in wide range of acidity [61]–[63]. The distribution ratios for Th(IV), U(IV),
and Pu(IV) are highest at 2-4 M nitric acid. The maximum for Np(IV) occurs at 3-4 M
nitric acid. The tetravalent actinides are extracted as hexanitrato complexes [61].
Figure 5-2 Aliquot-336 distribution ratio dependency on HNO3 concentration for various ions
103
The extractant is less effective for hexavalent actinides compared to tetravalent
species. The distribution ratios for Np(VI), U(VI), and Pu(VI) are about 2 orders of
magnitude less than the tetravalent species [63]. The distribution ratio for U(VI) reached
maximum at 6-7 M nitric acid concentration [61]. The extractability of U(VI) started to
decrease at 7 M nitric acid. This is believed to be due to the formation of inextractable
protonated complex H UO2(NO3) [63].
Aliquat-336 is used by Eichrom Technologies, Inc. to manufacture their TEVA®
branded resin. The resin is manufactured by coating the extractant onto a stable polymer
support. The main application for this resin is for separation of technetium and tetravalent
actinides and lanthanides.
5.1.1 PLF Preparation and Testing
Aliquat-336 was selected for a plutonium/uranium separation. PLFs were
prepared with solvent casting method with polystyrene and first tested with nitric acids to
ensure polymer structural agility under the harsh condition. The nitric acid test showed
that Aliquat-336 PLF was structurally unstable to be used with nitric acid. Figure 5-3 was
taken after Aliquat-336 PLF was exposed to the nitric acid. The polymer structure was
completely degraded, and PLF turned into a greenish color. Due to the instability of the
polymer film, Aliquat-336 PLF was not tested for plutonium extraction and no further
investigation was performed. TEVA® resin does not show any incompatibility with high
concentration nitric acid. In fact, the resin performed better for most analytes at high
nitric acid concentrations. The difference in the reaction shown by resin form and PLF
104
could be due to different preparation method or different polymer used as a support
matrix. TEVA is manufactured by coating Aliquat-336 onto Amberchrom CG-71ms [64].
Aliquat-336 PLF is prepared using polystyrene and ligand in strongly fixated onto the
polymer structure. Since H2DEH[MDP] PLF has shown ability to separate plutonium
from uranium, no other ligands will be investigated for the Pu/U separation scheme.
Figure 5-3 Aliquat-336 PLF damaged by high concentration nitric acid
5.2 4,4’,(5’)-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6)
Crown ether was first synthesized by Charles Pedersen in 1967. It is a cyclic
compound that uses its cavity structure to strongly bind to cations [65]. The 18-crown-6
variant of crown ethers is especially effective in strontium separation. The center cavity
of 18-crown-6 is used to extract strontium as illustrated in Figure 5-4 [66]. Cavity size is
the key to analyte extraction.
105
Figure 5-4 Strontium 18-crown-6 complex
Dicyclohexyl-18-crown-6 (DC18C6) and its variant 4,4’,(5’)-di-(tert-
butylcyclohexano)-18-crown-6 (DtBuCH18C6), shown in Figure 5-5, have been reported
by several authors to selectively form a strong complex with strontium over many
potential interfering elements [65], [67]–[70]. DtBuCH18C6 showed no ability to extract
Na(I), K(I), Fe(III), Al(III), Ca (II), Cs(I), La(III), Y(III), Ru(III), Mo(VI), and Pd(II)
[65], [70].
Figure 5-5 Chemical structure of (A) DC18C6 (B) DtBuCH18C6
DtBuCH18C6 ligand is also used in resin bead form. The product is commercially
available from Eichrom Technologies as Sr resin. The resin is manufactured by coating
1.0M DtBuCH18C6 in 1-octanol onto an inert chromatographic support. The bed density
of Sr Resin is approximately 0.35 g/mL [71].
106
Strontium extraction with DtBuCH18C6 ligand is highly dependent on the nitric
acid concentration [69]. The distribution ratio for strontium increases with increasing
nitric acid concentration. The highest strontium extraction occurs at 8 M nitric solution as
shown in Figure 5-6. The back-extraction of strontium can be performed by using low
concentration nitric acid as distribution ratio rapidly decreases at lower molar nitric acid
solution. DtBuCH18C6 also shows high affinity for Pu(IV) at high nitric acid
concentration. The k’ for Pu(IV) peaks out at 4M as shown in Figure 5-6.
Figure 5-6 DtBuCH18C6 distribution ratio dependency on HNO3 concentration for various ions
5.2.1 Plutonium Extraction
DtBuCH18C6 has shown affinity to plutonium in resin bead form. Based on that
fact, crown ether PLFs were prepared by solvent casting method and tested for plutonium
107
extraction. Four different ratio PLFs, 1:2, 1:5, 1:10, and 1:20, were tested with nitric
acids ranging from 0.01 to 8M. The four different PLFs synthesized with DtBuCH18C6
were all clear and there were no visual differences between them as shown in Figure 5-7.
Some of the PLF developed large bubbles along the edge. An equilibration time of 3
hours was used for the experiment.
Figure 5-7 Crown ether PLFs prepared with solvent casting method
All four DtBuCH18C6 PLFs were ineffective in plutonium extraction in the entire nitric
acid concentration ranges tested. The highest plutonium recovery was observed with 1:20
PLF and 0.1M nitric acid. However, the uncertainty was large and recovery was only
around 2.3%. Plutonium recoveries were plotted in Figure 5-8, which clearly show
ineffectiveness of DtBuCH18C6 PLF in plutonium extraction. The tracer solution was
collected and plated after 3 hour equilibration time to measure unextracted plutonium
activity. The PLF and electrodeposition data was computed to calculate unaccounted
activities and plotted in Figure 5-9. The unaccounted activities were consistently higher
than the PLF activities measured from alpha spectroscopy. The unaccounted activities
were relatively consistent from 0.01 to 1M nitric acid for all four ratio PLFs: about 31 to
38% activities were missing. At 8M nitric acid, unaccounted activities from 1:10 and
1:20 PLFs noticeably increased compared to the other nitric acid concentration tested. It
108
is suspected that high concentration acid is damaging the PLF and causing polymer
structure to be more porous to the solution. As the polymer medium becomes more
porous, higher amount of plutonium is penetrating through the PLF and deposited below
the surface.
Figure 5-8 Plutonium recovery by crown ether PLF as a function of nitric acid concentration
Figure 5-9 Unaccounted plutonium recovery by crown ether as a function of nitric acid concentration
23
28
33
38
43
48
53
0.01 0.1 1 10
Pu re
cove
ry (%
)
Nitric concentration [M]
1:2
1:5
1:10
1:20
109
The damages caused by 8M nitric acid are more noticeable in 1:2 and 1:5 DtBuCH18C6
PLF. The visible damage was significant and samples were not counted with alpha
spectroscopy due to the unstable nature of the PLF. Two data points were excluded in the
plutonium recovery plots in Figure 5-8 and Figure 5-9. The surface damages caused by
8M nitric acid are shown in Figure 5-10. Discoloration was observed in both 1:2 and 1:5
PLFs. Both PLF surfaces were etched by the acid. The degree of etching was greater in
1:2 PLF than 1:5 PLF. A close up image of 1:2 PLF shows extent of damage caused by
nitric acid. It is clear that the large amount of ligand in the PLF body is causing PLF to be
more prone to damage caused by high concentration nitric acid.
Figure 5-10 Crown ether PLFs damaged by high concentrated nitric acid
5.2.2 Strontium Extraction
The main goal of the study is to separate 90Sr from its daughter 90Y. 90Sr is a pure
beta emitter with a half-life of 28.8 years. It reaches secular equilibrium with its daughter
90Y, another beta emitter, in about 25 days. Simultaneous measurement of both nuclides
is impossible due to a beta energy continuum. It is essential to separate strontium from
110
yttrium to accurately quantify the activity of strontium with a beta counter. DtBuCH18C6
is a highly effective extractant for strontium but it has no affinity towards yttrium.
The strontium extraction was approached slightly differently than the plutonium
extraction since it is a beta emitter. PLFs for plutonium extractions were designed to be
used in a semiconductor based alpha spectroscopy, which is not an ideal system to
measure beta energy emitted by strontium. Liquid Scintillation Counter (LSC) is better
suited to measure the strontium decay energies. Due to the different counting system used
in strontium studies, The PLF was prepared in a glass LSC vial instead of a stainless steel
substrate. All other conditions were kept constant including PLF stock solution volume
used in preparing PLF. Figure 5-11 shows diagram of PLF coated LSC vial and actual
picture of the vial. PLFs were air dried for two days to evaporate THF and form a hard
polymer substrate.
Figure 5-11 Crown ether PLF coated LSC vial diagram
A strontium tracer in 3M nitric acid was used in the experiment. The solution was
directly transferred to the vial and equilibrated at three different time periods: 1 hour, 2
hours, and 12 days. LSC vials were agitated during the equilibration time except for the
111
12 day sample. Once the prescribed equilibration time was reached, the solution was
removed and the vial was thoroughly rinsed with deionized water. The solution and rinse
water were collected in a clean LSC vial to measure beta activity from the remaining
analytes. 15 mL of LSC cocktail was added to each sample before counting on LSC.
Each sample was counted for 1 hour and background count was subtracted from the
measurement. LSC data shows that DtBuCH18C6 PLF is not capable of extracting
strontium. PLF samples counted with LSC showed no measurable beta activities.
Strontium was not extracted but remained in the nitric acid solution. LSC measurements
from the remaining strontium tracer solution showed that the entire beta activity still
remained in the solution. Polystyrene support structure would be most likely the cause of
ineffectiveness of the ligand in strontium extraction. It is suspected that the polystyrene
chains are preventing the analyte from reaching the ring of the ether groups, which render
DtBuCH18C6 ineffective for strontium extraction.
5.3 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP])
2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]) is a phosphoric acid
based extractant, which shows effectiveness in rare earth and other metal elements
separation [72]–[77]. The ligand is developed by Daihachi Chemical Industry Company
Ltd and marketed with the trade name PC-88A. This ligand has similar chemical structure
as HDEHP. The main structure difference between HEH[EHP] and HDEHP is that an
oxygen is missing in one of HEH[EHP]’s hydrocarbon chains as shown in Figure 5-12. A
diluent with low aromatic content is recommended to use with this ligand [77]. The
112
ligand has been frequently used as an extractant for lanthanides in solvent extraction [73].
Number of elements were tested and show an affinity to HEH[EHP], including
lanthanides, thorium, and uranium [74], [75]. HEH[EHP] has shown great ability to
effectively separate individual lanthanides with high purity [78].
Figure 5-12 Chemical structure of HEH[EHP]
The ligand was also successfully used in resin bead form for the analyte
extraction. Resin beads were prepared by coating HEH[EHP] onto Amberlite XAD7
beads [73]. A mutual separation of Y-Gd, La-Pr-Nd, and Ho-Er-Tm was successfully
attained with the present resin as the stationary phase and hydrochloric acid as the mobile
phase [73].
A resin bead based extractant is commercially available by Eichrom Industry with
the trade name LN2. The resin bead extraction affinities to elements are shown in Figure
5-13. The anlatye extraction shows dependency on the nitric acid concentration.
Europium and americium uptake by the LN2 resin decreases as well when the pH
increase [72].
113
Figure 5-13 HEH[EHP] distribution ratio dependency on HNO3 concentration for various ions
Due to its similar chemical structure to HDEHP, analyte separation behavior of
HEH[EHP] is remarkably similar to the one observed with HDEHP as shown in Figure
5-14. The effectiveness of HEH[EHP] at rare earth extraction was slightly lower than
HDEHP. The extraction efficiency increases nearly linearly as the atomic number
increases.
114
Figure 5-14 HEH[EHP] distribution ratio relative to HDEHP [79]
5.3.1 Plutonium Extraction
HEH[EHP] is mainly designed for lanthanide separation; however, due to its
similarity to HDEHP, it has great potential to be also effective for plutonium separation
in PLF form. To test effectiveness of HEH[EHP] for plutonium extraction, 1:5, 1:10, and
1:20 PLFs were tested with 0.01 to 8M nitric acid by the direct stippling method. The
procedure used in this experiment was the same as the one employed in the HDEHP PLF
experiment. Plutonium extraction was most effective with 1:5 PLF in all nitric acid
solutions tested in the experiment. The plutonium recoveries by HEH[EHP] PLFs are
plotted in Figure 5-15. The plutonium percent recoveries by 1:5 PLF are ranging from 17
to 25%. 1:10 and 1:20 PLFs were generally ineffective for plutonium extraction in
conditions tested and plutonium recoveries for both PLFs were similar except for 0.1M.
115
The percent recovery for 1:20 PLF was about 10% compared to 5% for 1:10 PLF when
tested with 0.1M nitric acid. This plutonium extraction behavior at 0.1M nitric acid was
noticeable and unexpected. 1:20 PLF has less ligands than 1:10 and it was expect to had
lower amount of active site for analyte extraction. The reasons for such a behavior are
unknown and will need to be further investigated.
Figure 5-15 Plutonium recovery by HEH[EHP] PLF as a function of nitric acid concentration
Tracer solution that was left on PLF after 3 hour equilibration time was collected
and electrodeposited for the analysis. The data gathered from PLF and electrodeposited
samples were used to calculate the unaccounted activity from each sample. Figure 5-16 is
a plot of the computed unaccounted sample activities. The unaccounted activity was
assumed to be deposited below the surface and the activity was contained within the PLF
body. 1:5 PLFs consistently had higher amount of plutonium missing than 1:10 and 1:20
at the same condition. The unaccounted plutonium was higher than 60% for both 0.01
and 0.1M nitric acid solutions. This was the highest missing activity observed from any
0
5
10
15
20
25
30
35
0.01 0.1 1 10
Reco
very
(%)
Nitric Acid (M)
1:5
1:10
1:20
116
PLFs tested in entire thesis. This represented that close to 90% of the total plutonium
activity is deposited either on PLF surface or below the surface of 1:5 PLF with 0.01 or
0.1M nitric acid. This represented significant activity recovery, which was close to one
achieved by the conventional electrodeposition method. The limitation of HEH[EHP]
PLF was that even though the entire plutonium extraction percent was high, most of the
activity was contained below the surface. The sample with high internal alpha activity is
not an ideal sample for the silicon based alpha spectroscopy system.
Figure 5-16 Unaccounted plutonium recovery by HEH[EHP] as a function of nitric acid concentration
One noticeable and unexpected behavior of HEH[EHP] PLF was that 1:10 has
lower plutonium recovery than 1:20 PLF. Since 1:5 PLF had the highest total plutonium
recovery, it was expected for 1:10 PLF to perform better in plutonium extraction than the
1:20 PLF due to the higher amount of ligand incorporated into the polymer structure.
Also, since HEH[EHP] is structure analog of HDEHP, extraction behavior was expected
to be similar. In HDEHP PLF studies, plutonium recovery increased as a function of
-20
-10
0
10
20
30
40
50
60
70
80
0.01 0.1 1 10
Reco
very
(%)
Nitric Acid (M)
1:5
1:10
1:20
117
ligand mass. The reason for such behavior is not fully understood and will need to be
further investigated.
Due to lower surface plutonium extraction by HEH[EHP] than either HDEHP or
H2DEH[MDP] PLFs, there was no merit in using HEH[EHP] for plutonium extraction at
this point. No further studies were carried out for this ligand. The overall performance
this ligand may be improved by concentrating ligands on the surface of the PLF.
However, it is out of the scope of this thesis.
118
6. Chapter 6
Environmental Sample Analysis
PLFs were developed as a field deployable technique. It is important to test PLF
in relevant environments with appropriate samples to fully understand the capabilities
and limitations of the extractant system. H2DEH[MDP] PLF was exclusively used in this
chapter. Environmental samples were divided into two categories: liquid and solid.
Different types of samples require distinctive sample preparation procedure. Solid
samples are generally harder to process compared to liquid samples. Solid samples first
need to be completely dissolved into a solution to measure complete content of alpha or
beta analytes. Complete dissolution of a sample is generally time consuming and a
complicated procedure. Another approach is to leach out analyte of interest from the solid
matrixes. This method may not completely extract analytes from the solid matrixes but it
would offer simpler approach than the complete dissolution method. Leaching is ideal for
preparing samples for isotopic measurements where the entire analyte content is not
needed to perform a reliable analysis. The field deployable procedures were established
for water and soil samples. Two soil samples were examined: National Institute of
Standards and Technology (NIST) Rocky Flats soil Standard Reference Material (SRM)
and Mortandad Canyon soil in Los Alamos. Water samples were also collected from
Mortandad Canyon.
119
6.1 Soil Sample Analysis
Leaching and fusion procedures were established for the soil samples. The
procedures were kept simple as possible to be able to perform out in the field. Field
deployable methods would have great limits on reagents that can be transferred and used
due to the regulations and limitations in a deployed facility.
6.1.1 Soil Characterization
The environmental soil samples were collected from the creek bed in Mortandad
Canyon. The soil samples were characterized before the leaching or fusion studies due to
the lack of any prior knowledge on the sample. The soil samples were first analyzed with
a high purity germanium (HPGe) detector system. Gamma spectroscopy is a non-
destructive technique and requires little sample preparation before the analysis. Soil was
dried in a muffle furnace for 48 hours. Dried soil was placed in four circular containers
(pucks) as shown in Figure 6-1 and analyzed with HPGe detectors.
Figure 6-1 Mortandad Canyon soil samples
120
About 33g of soil was contained in each puck and gamma spectroscopy shows similar
spectra for all four samples. The spectra are attached in Appendix D and activities from
radionuclide measured with HPGe are given in Table 6-1. The highest activity was from
228Ac, which has half-life of 6.15 hours and decay to 228Th.
Table 6-1 Mortandad Canyon soil radionuclide activities measured with HPGe Radionuclide Activity (dpm/g)
137Cs 11.880±1.022 212Pb 32.574±1.882 226Ra 1.544±0.087 228Ac 204.946±15.412 235U 0.369±0.030
241Am 3.303±0.169
Elemental composition of Mortandad Canyon soil was further analyzed with the
neutron activation analysis (NAA). The analysis was performed at the Radiation Science
& Engineering Center at Penn State University. Two sets of 500 mg of Mortandad
Canyon soil were irradiated for 2 hours at a power level of 200 kW. The flux was
approximately 2x1012 n/cm2-s at the irradiation position. The comparative analysis was
performed by irradiating two NIST certified standard reference materials simultaneously
with the sample. The reference materials used were SRM278 - Obsidian Rock and
SRM679 - Brick Clay. Samples and SRMs were analyzed with HPGe detector system
after decay time of 6, 10, 17, and 23 days. The result of NAA elemental analysis is shown
in Table 6-2.
121
Table 6-2 Elemental information gained from NAA
Element Concentration Sodium 3.37 ± 0.18 wt% Potassium 3.969 ± 0.264 wt% Chromium 4.63 ± 1.53 ppm Hafnium 4.2 ± 0.3 ppm Barium 244.9 ± 65.0 ppm Scandium 1.23 ± 0.08 ppm Rubidium 81.3 ± 9.7 ppm Iron 0.95 ± 0.05 wt% Ytterbium 2.33 ± 0.12 ppm Tantalum 1.0 ± 0.3 ppm Cobalt 1.30 ± 0.33 ppm
A fusion digestion was performed on the environmental soil samples to measure
plutonium activity from the soil. 1g of soil was placed in a zirconium crucible with 10g
of sodium hydroxide. Samples were then melted using a muffle furnace at high
temperature. Soil samples processed with the muffle furnace are shown in Figure 6-2.
Once soil was fused, sample was removed from the crucible using DI water. The samples
were then filtered on a 0.8 μm pore size filter paper. Filtered analytes were then
redissolved by running 8M nitric acid through the filter. Column chromatography was
performed to isolate plutonium from other analytes before electrodepositing onto
stainless steel substrate. 12 ml of Bio-Rad AG 1x4 resin was used in the cleanup and
plutonium was eluted with 1.2M HCl-H2O2. 1.761 dpm/g and 6.088x10-1 dpm/g were
measured using a fusion procedure for 239+240Pu and 238Pu, respectively.
122
Figure 6-2 Fusion sample (A) before (B) after processing with the muffle furnace
The great advantage of fusion over other sample preparation techniques is that the
entire sample is digested, dissolved and analyzed. However, the fusion process is
complex and time consuming. Since the entire sample was dissolved, an extensive sample
cleanup was requried to process the sample. The fusion in conjunction with the classical
sample preparation chemical process took few days from start of dissilution of the sample
until the alpha analysis was complete.
6.1.2 Mortandad Canyon Soil Leaching Study
The analyte leaching process will offer more ideal solution to processing samples
out in the field. The main focuses in developing this process were to minimize use of
reagents and simplifying the procedure. The Mortandad Canyon soil and Rocky Flats
standard soil were used to establish the leaching procedure. The canyon soil samples
were used as is without any processing, including homogenization. The sample variation
would be higher without the homogenization, but the process is time consuming and may
be inadequate to perform in the field. The analyte leaching was performed using white
distilled vinegar and nitric acid. Vinegar is easy to purchase and there is no regulation
123
limiting transferring of material, which make it a good candidate for field use. However,
vinegar is a weak acid and the distilled vinegar is only 5% acetic acid. Nitric acid is more
favorable for the leach operation but transportation is regulated by U.S Department of
Transportation [80]. In this experiment, white distilled vinegar and concentration of nitric
acids ranging from 0.1 to 16M were tested to leach analytes from the soil. Roughly 10g
of soil and 20g of reagent were used per each sample. Samples were vortexed for
approximately a minute to suspend particles in solution then left to settle down for 24
hours. Samples were centrifuged to separate soil from solution then filtered with 0.02 μm
pore size syringe filter. Filtering process removed fine particles from the reagent and
difference made by filtering can be seen in Figure 6-3.
Figure 6-3 Leached solution (A) before (B) after syringe filtering
The aliquot of leached solutions were first analyzed with ICP-MS to gain
elemental information. Rest of samples were processed and counted with alpha
spectroscopy to measure activity. Nitric acid was able to extract many elements from the
soil. The elemental information is given in Table 6-3. The mass spectroscopy
measurement showed that the iron was the most abundant element in the leached
solution. The iron content was still low to be visibly observed from the leach solution.
124
Table 6-3 Elements leached from Mortandad Canyon soil using nitric acid
1M nitric acid 8M nitric acid 16M nitric acid Arsenic (ng/mL) 7.79±1.29 15.50±1.70 15.22±0.89 Yttrium (ng/mL) 243.40±17.95 243.47±11.25 283.28±10.86
Zirconium (ng/mL) 9.93±2.75 74.58±5.04 110.98±6.15 Niobium (ng/mL) 2.32±0.45 4.85±0.65 1.86±0.37
Molybdenum (ng/mL) 1.80±1.17 5.71±1.45 6.19±1.44 Cadmium (ng/mL) 1.54±0.57 1.50±0.45 2.21±0.44
Tin (ng/mL) 3.25±0.81 3.57±0.67 2.67±0.71 Barium (ng/mL) 799.33±67.20 700.04±42.72 686.72±40.37
Lanthanum (ng/mL) 530.70±35.50 485.22±19.14 517.50±19.67 Cerium (ng/mL) 656.14±39.06 982.87±40.84 793.06±30.09
Praseodymium (ng/mL) 139.41±8.46 128.15±5.10 135.67±5.84 Neodymium (ng/mL) 503.75±31.07 461.34±19.34 492.89±21.16 Samarium (ng/mL) 93.31±5.79 85.36±4.33 92.84±4.32 Europium (ng/mL) 4.24±0.30 3.84±0.23 4.86±0.22
Gadolinium (ng/mL) 109.41±7.47 103.85±5.54 113.34±6.05 Terbium (ng/mL) 11.07±0.72 10.52±0.47 11.46±0.49
Dysprosium (ng/mL) 50.54±3.20 49.19±1.94 54.19±2.09 Holmium (ng/mL) 9.65±0.60 9.39±0.40 10.50±0.48 Erbium (ng/mL) 26.15±1.92 25.66±1.54 28.90±1.76 Thulium (ng/mL) 3.13±0.28 3.16±0.18 3.43±0.19
Ytterbium (ng/mL) 21.34±1.58 21.36±1.04 23.40±1.24 Lutetium (ng/mL) 2.84±0.17 3.01±0.22 3.27±0.18 Hafnium (ng/mL) 0.83±0.28 2.98±0.35 4.39±0.60
Lead (ng/mL) 543.81±36.52 207.17±11.69 211.50±11.41 Thorium (ng/mL) 44.19±4.21 54.31±4.31 64.17±4.23 Uranium (ng/mL) 6.49±0.79 6.51±0.65 6.72±0.59 Rubidium (ng/mL) 7.20±1.15 22.44±2.30 17.87±1.70 Strontium (ng/mL) 101.58±26.09 68.31±17.78 85.89±16.69 Sodium (ng/mL) 2278.91±1252.26 2489.30±1029.05 1801.09±1287.47
Magnesium (ng/mL) 2903.35±486.19 2770.15±721.12 2319.07±526.21 Potassium (ng/mL) 4303.74±343.62 4704.81±282.30 4778.59±244.43 Titanium (ng/mL) 141.90±78.30 310.91±128.06 11.88±59.19
Vanadium (ng/mL) 23.12±31.34 48.98±29.10 27.25±23.08 Chromium (ng/mL) 95.18±12.77 23.47±12.50 26.34±8.00 Manganese (ng/mL) 3347.92±235.78 3967.06±222.38 4585.73±206.77
Iron (ng/mL) 25568.97±2776.14 40229.32±2809.24 30530.60±3007.38 Cobalt (ng/mL) 14.91±4.31 17.31±2.49 18.10±2.03 Nickel (ng/mL) 51.35±43.69 29.20±43.06 39.72±34.73 Zinc (ng/mL) 860.71±139.41 688.31±157.56 730.88±337.02
125
The soil samples from Mortandad Canyon soil had about 1% (wt) of iron, and only
5.11x10-3% of iron from soil was leached using 1M nitric acid. The leached solutions
were processed with the classical column chromatography and electrodeposition to
measure plutonium activity in the leach solutions. The plutonium leaching capacities
increased with the nitric acid concentration. 239+240Pu and 238Pu activities leached with
nitric acids are plotted in Figure 6-4. 1 to 16M nitric acids were all effective in leaching
plutonium out of the soil. The highest plutonium recoveries were achieved with 16M
nitric acid. Since lower nitric acid is easier to handle and process, 1M nitric acid was
further studied for analyte extraction in the time dependency experiment.
Figure 6-4 Plutonium leaching dependency on the nitric acid concentration
The leaching dependency on time was tested from 1 to 24 hours. All samples
from the time study showed measurable plutonium activities. 239+240Pu leached activities
are plotted in Figure 6-5 and it shows a logarithmic trend. The 24 hour leaching extracted
about 0.38 dpm/g, which was four times lower than one achieved from the previous
0
0.5
1
1.5
2
2.5
0.01 0.1 1 10 100
Pu A
ctiv
ity p
er g
ram
of s
oil (
dpm
/g)
Nitric Concentration (M)
239+240Pu
238Pu
126
study. The procedure was identical between two studies. Most likely the cause of the
discrepancy is due to unhomogenized soil. Soil was collected in the same location on the
same date but there were still possible variations from sample to sample. White distilled
vinegar was generally ineffective in leaching plutonium from the soil sample. The leach
capacity of the vinegar reached maximum around 2 hours then slightly decrease
thereafter.
Figure 6-5 Plutonium leaching dependency on time for 1M ntiric acid and white distilled vinegar
Mortandad Canyon leached samples were further processed with 1:20
H2DEH[MDP] PLF. In this study, leaching time and exposure time were varied to find
the most optimal time to process soil sample with PLF. Analytes were leached out from
soil by placing samples in 1M nitric acid for 1, 2, 3, or 24 hours. Nitric acid solution was
removed then syringe filtered after the prescribed leaching time. 3 mL of leached solution
was directly stippled onto PLF then removed after prescribed exposure time. The
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 5 10 15 20 25 30
239 P
u Ac
tivity
per
gra
m o
f soi
l (dp
m/g
)
Time (hr)
1M nitric
Vinegar
127
exposure times were also varied from 1 to 3 hours. Overall 239Pu activities were low for
the entire samples prepared with Mortandad Canyon soil as shown in Figure 6-6. Even
with the low plutonium recovery, plutonium peaks were easily distinguishable above the
background with 24 hour counts. PLF samples prepared with 24 hour leaching solution
had noticeably higher plutonium activities than the rest of the samples. The highest
239+240Pu activity of 0.315 dpm was seen with 24 hour leaching and 3 hour exposure. Soil
leaching time between 1 and 3 hours showed no difference in plutonium extracted onto
PLF surface.
Figure 6-6 239+240Pu extracted with 1:20 H2DEH[MDP] PLF at different leaching and exposure time
6.1.3 Rock Flats Soil Leaching Study
The leaching study was also performed with Rocky Flats soil. The leaching
procedure was the same as the one used with Mortandad Canyon soil. The Rocky Flats
soil is a NIST standard reference material, which was collected from Rocky Flats Plant in
Colorado. The soil was homogenized with an air jet mill to an average particle diameter
0.0E+00
5.0E-02
1.0E-01
1.5E-01
2.0E-01
2.5E-01
0 1 2 3 4
239+
240 P
u ac
tivity
(dpm
)
Exposure time (hrs)
1 hr
2 hrs
3 hrs
24 hrs
Leaching time
128
of 8 μm and more than 99% of the particles were less than 20 μm in diameter [81]. The
soil is a certified standard and information is given in Table 6-4. 240/239Pu ratio is not
certified and only uncertified value is listed on the material certification.
Table 6-4 Rocky Flats standard soil certified radionuclide activities Radionuclide Activity (mBq/g)
238Pu 0.278±0.041 239+240Pu 16.8±1.8
238U 39.6±3.0 234U 40.4±3.0 235U 1.88±0.53 90Sr 10.5±1.3
Vinegar and nitric acids were used as the leaching reagents. The Rocky Flat standard soil
was noticeably finer than the Mortandad Canyon soil. Roughly 10g of soil was
transferred to a centrifuge tube and 20g of reagent was added to the soil. Samples were
vortexed for approximately a minute to suspend particles in the solution then left to settle
for 24 hours. Particle sizes were small and portion of soil floated on the nitric acid.
Samples were centrifuged to separate soil from nitric acid solution. Once the soil had
settled, solutions were removed and filtered with a syringe filter to remove any particles
larger than 0.02 μm. Solution colors differ vastly based on the acidity as shown in Figure
6-7 and Figure 6-8. The darker color indicated that iron was also extracted from the soil.
129
Figure 6-7 Rocky Flats soil leaching with vinegar or various concentration nitric acid solutions
Samples were traced with 242Pu and cleaned using column chromatography before
electrodeposition. Alpha spectroscopy showed that 8 and 16M nitric acids were able to
leach plutonium out of the soil matrix. 40% and 82% of 239+240Pu activity was extracted
from the Rocky Flat soil with 8M and con nitric acid, respectively. 239+240Pu activity
removed by vinegar and nitric acids are shown in Table 6-5. 238Pu content in the soil
sample was too small to be effectively leached and measured with alpha spectroscopy.
Figure 6-8 Rocky Flats soil leached solutions after syringe filtering
130
Table 6-5 239+240Pu leached activities from Rock Flats soil and percent activity recoveries based on certified values
Leaching reagent 239+240Pu activity (dpm/g) Percent 239+240Pu leached (%)
Vinegar (2.758±1.625)x10-3 0.27±0.16 0.1M nitric acid (1.942±1.942)x10-3 0.19±0.19 1M nitric acid (2.118±0.397)x10-2 2.10±0.45 8M nitric acid (3.969±0.305)x10-1 39.37±5.19 16M nitric acid (8.248±0.359)x10-1 81.82±9.46
The Rocky Flats soil was further analyzed with 1:20 H2DEH[MDP] PLF. Based
on the leaching information, analytes were leached from the soil using 8 and 16M nitric
acids. Most leached samples were centrifuged then filtered with 0.02 μm pore size
syringe filter to remove any particles. One sample was processed without centrifuging to
check the possibility of skipping the step. A centrifuge may not be available out in the
field and it will be beneficial to possibly eliminate the step. The sample was processed
with a combination of filter paper and syringe filter. Without centrifuging the sample,
there was no clear separation between liquid and soil. Filtering took a long time and
became a cumbersome process due to the large amount of finely grounded soil that was
suspended in a solution. The filter paper was quickly clogged up by the soil and had to be
consistently replaced to effectively filter the soil. All samples were traced with 242Pu then
dried on a hot plate. A large amount of brownish residue was left in the beakers as shown
in Figure 6-9. The uncentrifuged sample had slightly darker color than the centrifuged
samples. The residues were redissolved by adding 3mL of 0.1M nitric acid. The nitric
acid was then stippled onto a PLF. The difference in the solution color between
centrifuged and uncentrifuged samples was clearly shown after stippling as shown in
Figure 6-10. Stippled solutions were removed after 3 hour exposure. PLFs were
thoroughly rinsed with DI water and showed no discoloration after the exposure.
131
Figure 6-9 Residue left on beaker after leached nitric acid was dried
Figure 6-10 Rocky Flats leached solution stippled on 1:20 H2DEH[MDP] PLFs
All samples were analyzed with alpha spectroscopy to measure plutonium. No activity
above the background level was measured for all samples. Even 242Pu tracer was not
extracted by PLF. It is a good indication that high concentration of iron was precipitating
plutonium out of solution, which rendered PLF inactive for the analyte extraction. The
elemental composition of the Rocky Flats SRM soil is shown in Table 6-6 [81]. The
elemental composition was measured using X-ray fluorescence (XRF). Relatively large
concentration of iron was presented in the soil and nitric acid was also leaching large
quantity of iron from the soil matrix. The current leaching procedure is inadequate for
soil with large iron content. The procedure had to be modified to remove iron from
solution for PLF to be effective in plutonium extraction. One way to eliminate iron is to
use hydrogen peroxide to convert Fe(II) in Fe(III) then filter iron precipitates from the
solution.
132
Table 6-6 Elemental composition of Rocky Flats SRM Element Mass percent (%) Element Mass percent (%) Silicon 36 Chlorine 0.004 Aluminum 4.5 Chromium 0.033 Iron 2.6 Copper 0.003 Magnesium 0.29 Gallium < 0.001 Calcium 0.40 Nickel 0.018 Sodium 0.65 Lead 0.003 Potassium 1.7 Rubidium 0.007 Titanium 0.20 Strontium 0.011 Phosphorus 0.07 Vanadium 0.004 Manganese 0.054 Yttrium 0.002 Carbon 1.5 Zinc 0.007 Sulfur 0.02 Zirconium 0.02
6.2 Water Sample Analysis
Water samples were also collected from Mortandad Canyon and used to establish
PLF procedures. Water samples were simpler to process than solid samples. Analytes
were already in solution and the procedure could be simplified compared to solid
samples. Two approaches were taken to prepare environmental water samples. The first
approach was to directly stipple solution on PLF without any chemical processing. The
second approach is to acidify water with nitric acid before processing with PLF.
6.2.1 Environmental Water Characterization
Mortandad Canyon water was first analyzed for plutonium and uranium contents.
500mL of water was traced with 242Pu and cleaned up using column chromatography. 12
ml of Bio-Rad AG 1x4 resin was used in the cleanup and plutonium was eluted with
1.2M HCl-H2O2.
133
Plutonium activities were low for the Mortandad Canyon water. 4.35x10-3 dpm/ml
of 239+240Pu and 9.38x10-4 dpm/ml of 238Pu were measured with electrodeposited samples.
The activities may be too low to effectively analyze with the PLF method. Only about
3mL solution can be stippled onto a standard PLF and that translates to 1.31x10-2 and
2.81x10-3 dpm for 239+240Pu and 238Pu, respectively for each sample. Typical sample
activities will be a lot lower considering the efficiency of the PLF system.
6.2.2 Environmental Water Processing with PLF
The pH of the solution is a critical parameter in the extraction of plutonium from
solution with H2DEH[MDP] PLF. Previous studies showed that H2DEH[MDP] PLF
performed well between 0.01 to 1M nitric acids. PLF analyte extraction capability at
natural pH was not examined in previous experiments. In this section, PLFs were tested
with environmental samples to examine the effectiveness of H2DEH[MDP] PLF in
natural pH. Also, PLFs were carefully examined for any physical degradation caused by
the environmental samples.
The procedure was kept as simple as possible. The environmental sample was
only cleaned with a syringe filter then directly stippled onto PLF for three hours. The
water was relatively clean and only a minimum amount of particulates were visible. The
procedure was simple and easy to perform in any setting. However, alpha spectroscopy
measurements showed no detectable plutonium activities. This is most likely due to the
low activities in the water samples. Also, the non-detectable activity could be due to
ineffectiveness of PLF in natural pH solution. Mortandad Canyon water had relatively
134
low plutonium content for the experiment, but it was the only contaminated
environmental water sample available for the PLF experiment. It was decided to prepare
a simulated water sample to best emulate a higher activity environmental sample. 242Pu
was first dried in a beaker, then filtered Mortandad Canyon sample was added to re-
dissolve plutonium. The simulated water was tested with the stippling method. The 242Pu
recovery by 1:20 H2DEH[MDP] PLFs were low at about 2.5% as shown in Table 6-7.
However, activity was detectable with the silicon alpha spectroscopy system and it was
well above the background. This experiment clearly demonstrated that PLF is capable of
extracting plutonium from environmental sample at natural pH. The procedure was
simple and did not require any addition of chemical reagents, which made it more
suitable field sample preparation than the conventional technique.
Table 6-7 Simulated environmental water sample plutonium recoveries Sample Type Pu Recovery (%) Natural pH 2.45±0.34 Acidified 41.32±5.95
H2DEH[MDP] PLF has performed well between 0.01 to 1M nitric acids in
previous experiments. Mortandad Canyon water had pH of 6. To put the water sample in
more favorable condition for analyte extraction, nitric acid was added to acidify the
filtered sample. The solution was then stippled on PLFs for three hours to extract
plutonium. No detectable plutonium was extracted from Mortandad Canyon water by
PLF. Since low pH was more favorable for plutonium extraction by H2DEH[MDP], the
low recovery was most likely due to the low plutonium content in the water samples. The
experiment was repeated with the simulated environmental water and showed
considerably higher plutonium recovery than non-acidified water. 41% of 242Pu was
135
recovered, which was about 17 times higher recovery than one seen from the non-
acidified sample.
6.3 Environmental Sample Analysis Conclusions
Procedures were established to process environmental samples with
H2DEH[MDP] PLF. The fusion digestion was performed using sodium hydroxide with
zirconium crucible. The method dissolved the entire sample and an extensive sample
cleanup was required to process the sample. The plutonium analysis using fusion method
took a few days from start of the fusion to the alpha counting. The leaching procedure
was developed to shorten and simplify the soil sample processing with PLF. Nitric acid
was able to leach plutonium out of Mortandad Canyon and Rocky Flats soils. However,
only plutonium leached out from Mortandad Canyon was extracted from the solution
using PLF. Overall 239Pu activities were low for the entire samples prepared with
Mortandad Canyon soil. 0.315 dpm of 239+240Pu was the highest activity measured using
PLF system. Even with the low plutonium recovery, plutonium peaks were
distinguishable above the background with 24 hour counts. The ICP-MS measurement
done on the Mortandad Canyon leached solution showed that nitric acid was able to leach
many elements along with plutonium. Out of elements measured with the mass
spectroscopy, iron was the most abundant element in the leached solution. The soil
samples from Mortandad Canyon soil had about 1% (wt) of iron and 5.11x10-3% of iron
from soil was leached using 1M nitric acid.
136
Rocky Flats soil was not effectively processed with PLF. Plutonium was not
extracted by PLF from the Rocky Flats leached solution. Rocky Flats samples contained
2.6% (wt) of iron and it leached together with plutonium. The leached solutions from the
Rocky Flats soil had dark reddish color. High concentration of iron interfered and
prevented plutonium from being extracted from solution by PLF. Even 242Pu tracer added
to the sample was not extracted by PLF. The leaching procedure would need to be
modified to process soil samples with high iron concentration.
Water samples were simpler to process with PLF than soil samples.
Approximately 2.5% of plutonium was extracted with 1:20 H2DEH[MDP] PLF by
directly stippling water onto PLF. The plutonium extraction was greatly increased by
acidifying the environmental water with nitric acid then stippled onto PLF. About 41% of
plutonium was recovered after acidifying the sample. Acidification of natural pH sample
is preferable due to higher plutonium recovery it provided compared to non-acidified
samples. However, if initial sample activity is high enough, environmental water can
directly be processed with PLF without adding any reagent to a sample.
137
Chapter 7
Summary and Conclusions
The goal of this research was to develop a novel method to selectively and rapidly
extract uranium, plutonium, and strontium from solutions using Polymer Ligand Film
(PLF). PLF was synthesized and tested for their ability to absorb radionuclides directly
from solutions and produce sources of sufficient quality for radiometric techniques. High
sample throughput is critical in an emergency response since there is a potential for
enormous number of samples. Current radioanalytical techniques are not well suited for
rapid analysis or pre-screening large numbers of samples to decide which to move onto a
more accurate but time consuming set of analyses. Conventional alpha spectrometry
techniques take a couple days to a week to complete depending on the sample. The newly
developed PLF method greatly shortens and simplifies the analyte extraction and sample
preparation for radiometric analysis. Samples can be analyzed within one to two days
using the PLF system.
Five different ligands were tested for the analyte extraction: bis(2-ethylhexyl)
methanediphosphonic acid (H2DEH[MDP]), di(2-ethyl hexyl) phosphoric acid (HDEHP),
trialkyl methylammonium chloride (Aliquat-336), 4,4'(5')-di-t-butylcyclohexano 18-
crown-6 (DtBuCH18C6), and 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]).
H2DEH[MDP] and HDEHP which showed effectiveness for plutonium extraction were
extensively studied. The extraction of strontium was exclusively studied with
DtBuCH18C6. In PLF form, DtBuCH18C6 became completely ineffective for strontium
extraction.
138
H2DEH[MDP] PLFs were effective in plutonium and uranium extraction.
H2DEH[MDP] performed best with 1:10, 1:15, and 1:20 ratio PLFs for the plutonium
extraction. 50.44% and 47.61% of plutonium were extracted on the surface of PLFs with
1M nitric acid for 1:10 and 1:20 PLF, respectively. H2DEH[MDP] PLF was also capable
of co-extracting or selectively extracting plutonium over uranium depending on the PLF
composition. With 1:5 PLF, 23% of plutonium and 20% uranium were simultaneously
extracted with 1M nitric acid. Unlike 1:5, both 1:10 and 1:20 PLFs were extracting
plutonium preferably over uranium under the same conditions. H2DEH[MDP] PLF
showed extraction consistency similar to the electrodeposited samples. The overall
analyte recovery was lower than electrodeposited samples. The typical electrodeposited
samples have analyte recovery of over 80%.
HDEHP PLFs were effective in plutonium extraction. 1:5 PLF showed best
combination of plutonium extraction and alpha spectrum resolution from the eight
different PLF compositions tested. The percent plutonium recovery was 49%, which was
higher than any other HDEHP PLFs except for 1:2 PLF. The main deficiency from 1:2
PLF is that the sample attenuation degraded the resolution of the alpha spectrum. 1:5 PLF
spectra had a tailing term of 18.65 based on the Bortels’ alpha peak fitting equation.
However, 1:2 PLFs showed 305.19 for the tailing. The spectra from 1:2 HDEHP PLFs
were unusable in any meaningful analysis due to the large tailing.
HDEHP PLF was surprisingly ineffective for uranium extraction from nitric acid.
The PLFs tested with natural uranium tracer showed no significant uranium recovery in
the entire conditions tested. The ligand itself is actually effective for both plutonium and
uranium in liquid/liquid and resin bead based extraction. The polystyrene structure is
139
causing ligand to behave differently than in other matrixes. One of the main deficiencies
of 1:5 HDEHP PLFs was inconsistency in plutonium recovery shown from different PLF
batches: one had three times higher plutonium recovery than the other.
Both H2DEH[MDP] and HDEHP PLFs were consistently susceptible to
plutonium penetrating and depositing below the surface. The internal radiation within the
body of PLF did not cause any spectra degradation. The analyte penetration issue was
beneficial in the TIMS analysis because the extra plutonium contained in PLF body gave
additional signal in the analysis. Plutonium was successfully back-extracted from PLFs
then processed for TIMS to measure plutonium isotopics. TIMS analysis was completed
without any issues and isotopic measurement was accurate.
Environmental samples were effectively processed with 1:20 H2DEH[MDP] PLF.
The extraction system was very effective in extracting plutonium from environmental
water samples with minimal sample processing. About 41% of plutonium was recovered
by first acidifying the water sample with nitric acid then stippling onto PLF. Soil samples
were more difficult to process with PLF. Analytes were first removed from the soil
matrices before being processed with PLF. Nitric acid was able to leach plutonium out of
soil samples along with other elements. The performance of PLF was highly dependent
on the composition of the soil. Samples with low iron content were processed with the
PLF system, and plutonium activities were measured with alpha spectroscopy. However,
processing samples with large iron concentrations were unsuccessful with the current
procedure. Also, the plutonium recovery was 30 to 40% lower with PLF compared to the
classical chemical procedure. Even with such limitations, the PLF technique simplified
the procedure and offered considerably reduced sample analysis time.
140
The PLF method is a great screening tool to deploy to decrease the number of
samples required for more extensive analysis. The entire sample preparation to analysis
was done within one to two days. The classical method for alpha samples takes two days
to a week in comparison. The technique also requires minimal chemicals, and it is field
deployable. The reduction in time and simplified procedure make this technique ideal for
the post-detonation emergency response.
7.1 Recommendations and Future Studies
It is important to further investigate the PLF extractant system with other relevant
sample types. During the incident response, various different types of samples will need
to be analyzed. As shown in soil analysis, the current leaching procedure is not adequate
to process all types of samples. Soil samples with large amounts of iron cannot be
processed with PLF. The interference introduced by iron is not unique to PLF, but it is a
well-known issue even for the classical sample preparation methods. The classical
chemical method uses column chromatography to separate plutonium from the rest of
analytes. The column chromatography for plutonium separation is well-established but
cumbersome and difficult to perform out in the field. Further investigation will be
performed to find simple process to remove iron from the leach solution. Another type of
sample that may be available at the incident location is fused nuclear explosion debris.
These samples are more complicated to process and nitric acid leaching will probably be
ineffective in removing plutonium from the matrix. The future studies will investigate the
possibility of using other chemicals to leach plutonium from fused debris samples. The
141
fusion digestion technique used to characterize the Mortandad Canyon Soil is also
capable of processing the refractory debris. The entire sample will be digested with this
technique and there might be elements that may cause the interference with analyte of
interest. A simple clean up procedure will be needed to remove these interferences
conjunction with the fusion technique.
All of the PLF preparation methods used in this study relied on the solvent to
dissolve the ligand and polystyrene. The solvent, THF, had a tendency to encapsulate in
the PLF medium and cause HDEHP PLFs to have inconsistency in plutonium extraction.
A further study is planned to modify PLF preparation method to be solventless. The
solventless PLF preparation method may make the PLF more consistent in the analyte
extraction and also eliminate the creation of bubbles in the PLF body.
Also, more experiments will be needed to shorten the total time needed for the
TIMS analysis for PLF samples. With the current method, the entire process takes least 3
to 4 days to complete. One way to decrease the time will be using a direct technique for
mounting plutonium onto TIMS filaments. Preliminary studies showed that direct
mounting has great potential to be utilized in TIMS analysis. It will decrease the analysis
time considerably and may even provide enhancement in the signal. Further studies are
required to fine tune the method to be effective.
142
Appendix A
Counting Software Code
The counting software was developed in C++ language in Microsoft Windows® environment. The plutonium locations from the digital autoradiography image were inputted into the software. The location information is divided into rectangular sections and plutonium distribution was analyzed.
#include <iostream> #include <fstream> #include <cmath> #include <iomanip> using namespace std;
int main() {
int mat[100000][2]; //Track locaton matrix double count[21][21]; //Counter for tracks in each section double x_range[21], y_range[21]; //Store section start & end of section int x_min, x_max, y_min, y_max; double x_sec, y_sec, total=0.0; int x_col; //Location matrix colume size double x_sub, y_sub; //Section size ifstream InFile("data.txt"); //input data from data.txt file ofstream OutFile("Track_data.cvs"); cout<<"Track Counting Software"<<endl; cout<<"------------------INPUT--------------------"<<endl; cout<<"How many sections in X: "; cin>>x_sec; cout<<endl<<"How many sections in Y: "; cin>>y_sec; InFile>>x_col; //Input colume size //Input track location for(int i=0; i<x_col; i++) { for(int j=0; j<2; j++) { InFile>>mat[i][j]; } } //Find min and max x_min=x_max=mat[0][0];
143
y_min=y_max=mat[0][1]; for(int i=0; i<x_col; i++) { if(mat[i][0]<x_min) x_min=mat[i][0]; else if(mat[i][0]>x_max) x_max=mat[i][0]; } for(int i=0; i<x_col; i++) { if(mat[i][1]<y_min) y_min=mat[i][1]; else if(mat[i][1]>y_max) y_max=mat[i][1]; } //Calculate section size x_sub=(x_max-x_min)/x_sec; y_sub=(y_max-y_min)/y_sec; //Store range info in an array x_range[0]=x_min; y_range[0]=y_min; OutFile<<"X range"<<endl; OutFile<<x_range[0]<<"\t"; for(int i=1; i<=x_sec; i++) { x_range[i]=x_range[i-1]+x_sub; OutFile<<x_range[i]<<"\t"; } OutFile<<endl<<"Y range"<<endl; OutFile<<y_range[0]<<"\t"; for(int i=1; i<=y_sec; i++) { y_range[i]=y_range[i-1]+y_sub; OutFile<<y_range[i]<<"\t"; } OutFile<<endl<<endl; //Counting tracks in each section. cout<<endl<<"------------------RESULT--------------------"<<endl; cout<<"Track counts per section:"<<endl; OutFile<<"Track counts per section:"<<endl; for(int i=0; i<y_sec; i++) { for(int j=0; j<x_sec; j++) { count[i][j]=0;
144
for(int k=0; k<x_col; k++) { if(mat[k][0]>=x_range[j] && mat[k][0]<x_range[j+1] &&
mat[k][1]>=y_range[i] && mat[k][1]<y_range[i+1]) count[i][j]++; else if (mat[k][1]==y_max) { if (mat[k][1]<=y_range[i+1] &&
mat[k][0]>=x_range[j] && mat[k][0]<x_range[j+1]) count[i][j]++; } else if (mat[k][0]==x_max) { if (mat[k][0]<=x_range[j+1] &&
mat[k][1]>=y_range[i] && mat[k][1]<y_range[i+1]) count[i][j]++; } else if(mat[k][0]>=x_range[j] && mat[k][0]==x_max &&
mat[k][1]>=y_range[i] && mat[k][1]==y_max) count[i][j]++; } cout<<count[i][j]<<"\t"; OutFile<<count[i][j]<<"\t"; } cout<<endl; OutFile<<endl; } cout<<endl; //Total track in sample for(int i=0; i<y_sec; i++) { for(int j=0; j<x_sec; j++) total=total+count[i][j]; } //Checking count data if (total==x_col) { cout<<endl<<"Total number of tracks in sample: "<<total<<endl; OutFile<<endl<<"Total number of tracks in sample: "<<total<<endl; cout.precision(2); cout<<endl<<"Area per section (pixel^2):
"<<double(x_sub*y_sub)<<endl; OutFile<<endl<<"Area per section (pixel^2):
"<<double(x_sub*y_sub)<<endl; }
145
//Calculating count uncertainty cout<<endl<<"Counting uncertainty per section: "<<endl; OutFile<<endl<<"Counting uncertainty per section: "<<endl; for(int i=0; i<y_sec; i++) { for(int j=0; j<x_sec; j++) { cout.precision(2); cout<<fixed<<double(sqrt(count[i][j]))<<"\t"; OutFile<<fixed<<double(sqrt(count[i][j]))<<"\t"; } cout<<endl; OutFile<<endl; } //Calculating percent distribution cout<<endl<<"Percent distribution of tracks per section: "<<endl; OutFile<<endl<<"Percent distribution of tracks per section: "<<endl; for(int i=0; i<y_sec; i++) { for(int j=0; j<x_sec; j++) { cout.precision(2); cout<<fixed<<double(count[i][j]/total*100.0)<<"%\t"; OutFile<<fixed<<double(count[i][j]/total*100.0)<<"%\t"; } cout<<endl; OutFile<<endl; } //Calculating track density cout<<endl<<"Track density per section (track/pixel^2): "<<endl; OutFile<<endl<<"Track density per section (track/pixel^2): "<<endl; for(int i=0; i<y_sec; i++) { for(int j=0; j<x_sec; j++) { cout<<scientific<<double(count[i][j]/(x_sub*y_sub))<<"\t"; OutFile<<scientific<<double(count[i][j]/(x_sub*y_sub))<<"\t"; } cout<<endl; OutFile<<endl; } cout<<endl<<"**Result is saved in Track_data.cvs file**"<<endl<<endl; return 0; }
146
B. Appendix B
H2DEH[MDP] PLF Plutonium Distribution Maps
H2DEH[MDP] PLF plutonium distribution maps were generated from digital autoradiography images. The location information was processed with the counting software in Appendix A.
Figure B-1 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2A)
Figure B-2 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2B)
147
Figure B-3 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2C)
Figure B-4 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2D)
Figure B-5 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2G)
148
Figure B-6 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2H)
Figure B-7 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2I)
Figure B-8 Plutonium distribution maps of H2DEH[MDP] PLF generated from digital autoradiography image (sample ID: 095JR2J)
149
C. Appendix C
HDEHP PLF Plutonium Distribution Maps
HDEHP PLF plutonium distribution maps were generated from digital autoradiography images. The location information was processed with the counting software in Appendix A.
Figure C-1 Plutonium distribution map of 1:2 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2A)
Figure C-2 Plutonium distribution map of 1:2 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2B)
150
Figure C-3 Plutonium distribution map of 1:2 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2C)
Figure C-4 Plutonium distribution map of 1:5 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2D)
Figure C-5 Plutonium distribution map of 1:5 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2E)
151
Figure C-6 Plutonium distribution map of 1:5 HDEHP PLF generated from digital autoradiography image (sample ID: 043JR2F)
152
D. Appendix D
Gamma Spectra from Mortandad Canyon Soil Samples
Figure D-1 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2A)
1.E+00
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1.E+04
1.E+05
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ts
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1.E+05
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ts
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153
Figure D-2 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2B)
Figure D-3 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2C)
Figure D-4 Gamma spectrum from Mortandad Canyon soil sample (sample ID: 149JR2D)
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
0 500 1000 1500 2000 2500 3000 3500 4000
Coun
ts
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1.E+00
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ts
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154
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Vita
Jung Rim was born in Seoul, South Korea. His family immigrated to the USA in
1996 and settled in northern Virginia. He started full time classes as an undergraduate at
The Pennsylvania State University in Fall of 2001. He received a B.S. in Nuclear
Engineering and a B.S. in Mechanical Engineering in 2006. He continued his studies and
received a M.S. in Nuclear Engineering in 2011. Jung earned his Ph.D. in Nuclear
Engineering from The Pennsylvania State University in December of 2013. He is a
member of the American Nuclear Society (ANS), American Chemical Society (ACS),
and the Alpha Nu Sigma Society. He is married to Miel Lim. Together they have one
daughter, Aleena Rim.