paul scherrer in st itu t december, 2007 i r · paul scherrer in st itu t i_r psi bericht nr. 07-05...
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P A U L S C H E R R E R I N ST I T U T
i_r
PSI Bericht Nr. 07-05 December, 2007 ISSN 1019-0643
Department Logistics Division for Radiation Safety and Security
Separation of Plutonium on the Anion Exchanger BIO-RAD 1-X2 and its Application to Radiochemical Analysis
Sixto Bajo, Cordula Gann, Jost Eikenberg, Leo Wyer, Heide Beer, Max Ruthi, Maya Jaggi and Irene Zumsteg
P A U L S C H E R R E R I N S T I T U T
r-PSI Bericht Nr. 07-05
December, 2007 ISSN 1019-0643
Department Logistics Division for Radiation Safety and Security
Separation of Plutonium on the Anion Exchanger BIO-RAD 1-X2 and its Application to Radiochemical Analysis
Sixto Bajo1, Cordula Gann, Jost Eikenberg, Leo Wyer, Heide Beer, Max Riithi, Maya Jaggi and Irene Zumsteg
1 email: [email protected]
Paul Scherrer Institut 5232 Villigen PSI Switzerland Tel. +41 (0)56 310 21 11 Fax +41 (0)56 310 21 99 www.psi.ch
Abstract This report describes the extensive utilization of the classical anion exchanger
BIO-RAD 1-X2 in 8 molar nitric acid for the separation of plutonium from matrices
such as air filters, concrete, cooling reactor water, faeces, smear reactor
samples, and soils, and for the purification of plutonium tracers. Detailed
procedures are given for all these matrices, from the dissolution of the sample to
the final electrodeposition preceding alpha spectrometry.
Also included is the behavior in the anion exchanger of potentially interfering
nuclides of elements such as Am, Np, Po, Th, and U. Special attention has been
given to the isotopic exchange between plutonium in the sample and the
plutonium tracer added for the recovery determination, as well as some usual
operations performed during the analysis.
Zusammenfassung In diesem Bericht werden die Moglichkeiten aufgezeigt, wie mit dem
klassischen Anionenaustauscher BIO-RAD 1-X2 in 8 molarer Salpetersaure
Plutonium aus verschiedenen Materialien getrennt werden kann oder Tracer
gereinigt werden konnen. Diese Trennung erfolgt aus Ausgangsmaterialien wie
Luftfilter, Beton, Reaktorkuhlwasser, Fakalien, Wischtestproben und Boden.
Detaillierte Aufschlussverfahren des Materials bis hin zur Auflosung der
Probe fur die Elektrodeposition zur anschliessenden Messung mittels Alpha-
Spektrometrie werden erklart.
Zusatzlich wird gezeigt, wie sich der Anionenaustauscher verhalt bei
mbglichen Nuklidinterferenzen der Elemente Am, Np, Po, Th und U. Speziell
herausgehoben werden der isotopische Austausch von Plutonium in der Probe
mit dem Plutonium-Tracer, welcher fur die Wiederfindungsrate verwendet wird,
und die Arbeitsschritte, die dazu benotigt werden.
j
Table of Contents
1. Introduction 1
2. Experimental and Results 2
2.1. Materials 2
2.2. Reagents and solutions 3
2.3. Unit operations 5
2.3.1. Sample decomposition 5
2.3.2. Evaporation 7
2.3.3. Column chromatography 8
2.3.3.1. Separations with the anion exchanger BIO-RAD 1 9
2.3.3.2. Separation of actinidesfrom pure actinide solutions 14
2.3.3.2.1. Discussion 15
2.3.3.3. Separation of Pu from other elements 17
2.3.3.4. Separation of Pu from Np 21
2.3.3.5. Anion exchanger regeneration 22
2.3.3.6. Anion exchanger stability 22
2.3.4. Electrodeposition 24
2.3.4.1. Cleaning of the components of the electrolytic cell 25
2.3.4.2. Etching of the actinides electrodeposited on the planchets 26
2.3.5. Isotopic exchange between sample and tracer 29
3. Applications 31
3.1. Purification of tracer solutions 31
3.2. Determination of actinides in primary coolant reactor water 32
3.2.1. Results 33
3.3. Determination of Pu in concrete 35
3.3.1. Sample dissolution 35
3.3.2. Preparation of the solution for the separation of Pu 37
3.3.3. Separation of Pu on BIO-RAD 1-X2 37
3.3.4. Results 37
3.4. Determination of Pu in air filters 38
3.4.1. Dry ashing of the deposit 40
ii
3.4.1.1. Total dissolution 41
3.4.1.1.1. Preparation of the solution for the separation of Pu 41
3.4.1.1.2. Separation of Pu on BIO-RAD 1-X2 42
3.4.1.1.3. Results 42
3.4.1.2. Leaching 42
3.5. Determination of Pu in faeces 43
3.5.1. Sample collection 43
3.5.2. Mineralization 44
3.5.2.1. Mineralization of the bulk of the samples by dry ashing 44
3.5.2.2. Finishing by wet ashing 45
3.5.3. Leaching 45
3.5.3.1. Preparation of the solution for the separation of Pu and other
actinides 46
3.5.3.2. Insoluble residue 47
3.5.4. Separation of Pu on BIO-RAD 1-X2 48
3.5.5. Results 48
3.6. Determination of Pu in smear reactor samples 52
3.6.1. Sample dissolution 52
3.6.2. Separation of Pu on BIO-RAD 1-X2 54
3.6.3. Results 55
3.7. Determination of Pu in soil 56
3.7.1. Mineralization of the organic matter by wet-dry ashing 56
3.7.2. Leaching of Pu 57
3.7.3. Separation of Pu on BIO-RAD 1-X2 58
3.7.4. Results 58
4. References 63
5. Appendix 68
5.1. Nuclear characteristics of some Pu isotopes 68
Ill
List of Tables
Table 1: Distribution coefficients of elements on a strong base anion exchange
resin in HCl solutions 10
Table 2: Distribution coefficients of actinides and other metal ions on strong base
anion exchange resins in HCl solutions 11
Table 3: Distribution coefficients of elements on a strong base anion exchange
resin in HNO3 solutions 12
Table 4: Distribution coefficients of actinides and other metal ions on strong base
anion exchange resins in HNO3 solutions 13
Table 5: Distribution of some actinides on BIO-RAD 1-X2 16
Table 6: Pu(IV) retained on the anion exchangers from pure HNO3 solutions. ...18
Table 7: Pu(IV) retained on the anion exchangers after washing with 10 M HCl.19
Table 8: Pu(IV) eluted from the anion exchangers as Pu(lll) by 9 M HCl 0.10 M
HI 19
Table 9: Separation of Pu(IV) on BIO-RAD 1-X2 from 8M HN03 solutions
containing also other solutes 20
Table 10: Capacity of the exchanger BIO-RAD 1-X2 after many regeneration
cycles (standard chromatographic column) 23
Table 11: Reagents and conditions used for etching the nuclides from the
planchets 27
Table 12: Nuclides remaining in the planchets after etching 28
Table 13: Isotopic exchange 242Pu(lV) - 239Pu(IV, VI) in the system HN03 - H202.
30
Table 14: Determination of actinides in reactor water (BWR) 34
Table 15: Determination of 239240Pu and 238U in shielding concrete 38
Table 16: Some possibilities for dissolution of actinides from aerosols deposited
on microfibre glass filters 40
Table 17: Results of different faeces weight fractions during the analysis 48
Table 18: Plutonium contents of dry ashed faeces NR-209 50
Table 19: Actinide contents of faeces ash samples (PROCORAD) for the period
1998-2002...........................................................................................................51
JV
Table 20: Determination of Pu in smear reactor samples 55
Table 21: Determination of 239240Pu in soils and sediments - Reproducibility. ...59
Table 22: Determination of 239240pu in soils and sediments - Accuracy 60
Table 23: Pu isotopic exchange between soil sample and tracer 62
1
1. Introduction
The element Pu (Z = 94) is a member of the actinide series of the elements (Z
= 89 (Ac) to Z = 103 (Lw)). The actinides have similar chemical properties and
are also similar to the lanthanides (Z = 57 (La) to Z = 71 (Lu)). An excellent
summary of the chemical properties of both series has been given by Seaborg
[1].
Sixteen isotopes of Pu have been synthesized, all of which are radioactive [2],
See also Appendix (Tables A-E).
The Pu present in the environment originates from the atmospheric nuclear
testings from 1950 to 1963, which produced the so-called "global fallout". As a
result. 6.5E15 Bq 239Pu (2.8 tons), 4.4E15 Bq 240Pu (0.52 tons), and 3.7E4 Bq 241Pu (0.04 tons) were dispersed over the world [3]. A contribution also to the
global fallout was the ignition of the satellite SNAP 9A in the atmosphere in 1964,
equipped with a battery powered by 6.3E14 Bq (1 kg) of 238Pu [4]. In addition to
these sources, nuclear reactors, reprocessing plants and radioactive waste
facilities may contribute with their emissions to increase locally the Pu
concentration in their environment.
In the PSI laboratory, we are confronted with the determination of traces of 238Pu and 2 3 9 2 4 0 p u in environmental and biological materials. Because of the low
quantity of Pu in the analyzed samples, which is usually below 100 mBq. it is
mandatory to separate the Pu from all other accompanying elements. The
separated Pu is then measured by alpha spectrometry.
In this work, the anion exchanger BIO-RAD AG 1 is extensively used for the
separation of Pu from different matrices. This exchanger is superior when only
Pu is determined in the sample. In addition, it is also very suitable when other
actinides, such as Am and Cm, are also determined. No preconcentration step is
necessary for the Pu separation. The resins introduced by the company Eichrom
Industries in the 90's, which allow the separation of the actinides from the major
environmental elements and from each other, requires relatively small volumes of
sample solution.
2
2. Experimental and Results
2.1. Materials
Anion exchangers. BIO-RAD 1-X8 resin, chloride form, dry mesh size 100-
200, wet bead size 106-180 Mm, Cat. No. 140-1441. BIO-RAD 1-X2 resin,
chloride form, dry mesh size 100-200, wet bead size 106-250 um, Cat. No. 140-
1241 Suplier: BIO-RAD Laboratories AG, CH-4153 Reinach.
Chromatographic column. BIO-RAD Econo-column (glas and polypropylene),
internal diameter 10 mm, length 200 mm (Cat. No. 737-1021). The bottom of this
column is fitted with a fixed porous polyethylene plate to support the bed
material. When passing aqueous solutions through a bed of 100-200 mesh resin,
the flow stops when the level of the solution reaches the top of the bed.
Therefore, the resin never runs dry, so enabling unattended operation. A glass
fiber filter disc (Whatman GF/B, diameter 10 mm) is placed on the top of the bed
by gentle tapping. This filter allows undisturbed operation of the resin bed and
acts as a diffuser. It is attacked by HF even so diluted as 0.02 M and must then
be replaced by a polyethylene filter. Such a filter, 10 mm in diameter, may be cut
from a porous polyethylene filter plate (1.6 mm thick, 70 micrometer, Semadeni
Art. 3919).
This column may be fitted with a BIO-RAD Econo-column funnel (250 ml,
polypropylene. Cat No. 731-0003). A two-way stopcock (Cat. No. 732-8102) may
be fitted to the male outlet of the column.
Standard chromatographic column. Unless otherwise stated, all Pu(IV)
separations were performed in a 10 mm internal diameter column (see above)
containing 2.0 g - as received- of BIO-RAD 1-X2. This quantity of anion
exchanger produces a bed which has a height of 45 mm when swollen in water
and 29 mm in 8 M HNO3. Thus, the volume of the exchanger is reduced to 64%
when the medium is changed from water to 8 M HNO3. In this latter medium the
exchanger bed volume is 2.3 ml and the free column volume (including the
porous plate and the stopcock) 2.8 ml.
3
Sometimes, in the preliminary experiments, a BIO-RAD 1-X8 exchanger was also
used in the 10 mm internal diameter column. Two grams -as received- of this
exchanger has a height of 40 mm when swollen in water and 36 mm in 8 M
HN03 .
Heating plate. A Thermolyne Cimarec 2 heating plate was used for all
evaporations and calcinations. Supplier: Ismatec SA, CH-4123 Allschwil. The
heating plate has the following characteristics: plate dimensions 180X180 mm;
power 1035 W. This corresponds to 3.2 W/cm2. The temperature measured by a
thermoelement dipped into 2 cm of fused Wood metal (Fluka Cat. No. 95430) in
a 25 ml glass beaker located in the center of the plate was 520 °C with the heater
at full power. An aluminium shield around the beaker is very convenient when
evaporating and calcining solutions in concentrated H2S04 to evaporate the last
droplets condensed in the rim of the beaker.
Electrodeposition unit. This outfit has been previously described [5. 6].
2.2. Reagents and solutions
Only some special reagents and solutions are given here.
Hydroiodic acid (HI), cone, 57%, D = 1.70 kg/I, 7.6 M, Merck Art. 1.00344.
This reagent has a yellow tint when received, and becomes dark brown with time,
due to oxidation of iodide to iodine. Even the practically black reagent retains its
capability to reduce Pu(IV) to Pu(lll) when eluting Pu from the anion exchanger
as detailed below.
1.00 M NaHS04. Dissolve 69.04 g NaHS04. H20, analytical quality, in
approximately 400 ml water in a 500 ml graduate flask and then add water to
bring the volume to the 500 ml mark. For work that is more precise, the following
procedure may be used: mix 71.02 g Na2S04, 49.039 g H2S04 (Merck
ampouleTitrisol Art. 1.09981) and approximately 500 ml water. Dilute the
resulting solution to 1000 ml with water. More diluted solutions were prepared by
diluting this solution with water.
4
Earth crust synthetic solution. Prepare a solution containing Al (16.5 mg/ml).
Fe (III) (11.3 mg/ml), Ca (8.3 mg/ml), Mg (4.7 mg/ml), Na (4.7 mg/ml). and K (4.2
mg/ml), by using nitrates, oxides or carbonates. The solution has to be 0.2 M in
free HNO3. The preceding elements are present in the same weight ratio as in
the average continental crust [7]. One ml of this solution corresponds to 0.2 g of
earth crust. The above given elements, in addition to O and Si, contribute to
about 99.5% of the crust. This solution was used to simulate soil solutions.
Radioactive tracers. Prepare solutions of 236Pu, 239240Pu, 242Pu, 241Am, 243Am, 237Np, and 232U/226Th containing an accurately known (in the range of 0.5-2
Bq/ml) concentration of the isotope by diluting the original stock standard solution
with 2 M HN03.
The preparation of Pu(IV) solutions in 0.10 M NaHS04 has been described in
[8], This procedure has also been used to prepare solutions of isotopes of other
elements in the same medium.
Practically all experiments were carried out with 50-200 mBq of tracer.
The advantages and disadvantages of the different Pu tracers (236Pu. 242Pu)
as well as those for other actinides have been discussed in the literature [9-13].
When it was necessary to purify a tracer, an aliquot of the original stock
solution was processed, and the resulting purified solution was standardized by
electrodepositing several aliquots as described [6].
Cleaning solutions. Solution A: A solution 0.5 M in HF. Solution B: A solution 0.40
M in NaHS04. 1.6 M in H2S04 l and 7.2 M in HN03 . Solution C: A solution 0.10 M
in H2C204.
5
2.3. Unit operat ions
2 . 3 . 1 . Samp le decomposi t ion
The sample matrix has to be decomposed to liberate the analyte so that it can
participate in the chemical reactions and thus be isolated from the interfering
elements. The aim of the decomposition process is to provide a solution which
contains all the analyte. This solution is the starting point of the separation
process.
An overview of decomposition methods for the determination of elements in
organic and inorganic matrices has been reported [14]. Some books about this
topic have been recently published [15 - 19].
When analyzing food, faeces, plants and soils for the determination of artificial
radioactive elements {isotopes of Pu, Am, Sr, etc) it is usual to begin the
decomposition process by a dry ashing to mineralize the organic matter. Usually
the ashing is carried out in an oven at 500 °C. Sometimes, a preashing at lower
temperature may be performed to char the sample -on a hot plate or in the oven-,
especially with fat rich materials such as whole milk powder. The obtained ash is
about 7% of the dry weight for plants and 80-95% of the dry weight for soils.
Plant ashes are mainly carbonates of Ca, Mg, and K, in addition to sulphates and
phosphates; soil ashes are mostly silicates, oxides, and carbonates. These
ashes contain minute quantities of carbon trapped in the inorganic salts. To
eliminate it, the ash may be heated to 700-800 °C. Nevertheless, at this
temperature the ash is sintered, which may produce very resistant compounds.
Therefore this method is not recommended, except for small samples (1-2 g),
and when a total dissolution method (fusion or HF treatment) follows the ashing.
In most cases, the ash is moist with 7-14 M HNO3, evaporated to dryness on
a hot plate and finally calcined in an oven at 400 °C for at least 30 min. Thus, the
nitrates of Ca, Mg and K in the ash oxidizes readily the remaining carbon leaving
behind a mineral residue absolutely carbon free. Magnesium nitrate is a very
helpful ashing aid which decomposes at about 400 °C liberating nitrogen oxides
6
and producing finally a MgO residue. These strong oxidizing nitrogen oxides
behave like a high temperature nitric acid. In the presence of organic matter,
Mg(NC>3)2 begins to decompose well below 400 °C. Although one treatment with
8 M HNO3 is practically always enough, addition of HNO3 to this ash regenerates
the Mg(N03)2 from the produced MgO. The Mg(N03)2 is a more powerful
oxidizing reagent than H2O2. In addition, the former proceeds smoothly, whereas
the later decomposes readily while evolving many gases, with the subsequent
spurting. In very poor Mg samples, Mg(N03)2 may be added.
To separate the analyte from the mineralized ash, leaching methods are
preferred over total dissolution methods, because they are quicker and combine
both dissolution and separation. The leaching reagents are usually medium
concentrated HCl or HNO3. The choice of the acid depends usually on the
composition of the ash and on which acid is required on the next separation step.
When determining isotopes of Pu, Am and Sr in soils contaminated by the
global fallout (Pu-bearing particles < 1 u.m) [20]), it may be remembered that
these isotopes are more or less integrated into the organic and the mineral
components of the soil. But they are certainly not integrated in the silicates
lattices. Therefore, in order to separate these isotopes from the soil components
it is not mandatory to bring the silicates into solution. The general practice [20]
has shown that a strong acid leaching is enough to liberate them. On the
contrary, the determination of Pu and other actinides in soils near the nuclear
bomb tests requires total dissolution of the sample, because they are
incorporated in the fused silicates [20. 21]. This is also true when determining the
natural isotopes of U and Th. which are present, at least partially, in the silicate
lattice.
When determining Pu in soils, several total dissolution methods by fusion
have been proposed: potassium fluoride followed by pyrosulfate [22 - 24], sodium
carbonate [25], lithium borate [26], sodium peroxide/sodium hydroxide [27], and
sodium hydroxide in an alumina crucible [28]. In general, samples containing
refractory Pu02 must be treated with HF or by fusion.
7
Leaching of soils with 8 M HN03, 0.9 M HF and 1 M HN03 2.3 M AI(N03)3
sequentially has been proposed for the quantitative extraction of Pu [29]. This
procedure is claimed to dissolve even the highly calcined PuO? present in
contaminated soils.
2.3.2. Evaporat ion
Evaporation is a concentration technique to separate the solute from the
solvent. This separation may be partial, giving a more concentrated solution, or
total giving a solid residue. The solvent is usually discarded (volatilized). This
process is mostly carried out in glass beakers on a hot plate, while keeping the
temperature of the solution under the boiling point during all the process to avoid
sputtering, with the subsequent losses and contamination of the surroundings. A
time switch controlled hot plate allows to heat at any rate for unattended
operation overnight. An air jet directed toward the liquid surface accelerates the
evaporation, although it is necessary to increase the heating power to
compensate for the air cooling effect.
Laboratory microwave ovens offer also the possibility to perform evaporations
with simultaneous trapping of the solvent [19].
It is recommended that the actinide solutions to be evaporated in glass or
Teflon beakers be at least 0.1 M in a volatile acid such as HN03or HCI. A Teflon
vessel must be used with alkaline solutions.
The dry residue has not to be overheated, especially weightless residues, to
avoid analyte retention on the beaker's bottom. A simple method to bypass this
problem is by adding an evaporating aid such as NaHS04 [24] or Mg(N03)2 to
the solution before evaporation. They provide a solid substrate, which dilutes the
solute and therefore reduces the possibility to react with the beaker's bottom.
Less than 50 mg are needed from these evaporation aids, and usually a few mg
are enough. Both reagents, NaHS04 and Mg(N03)2, evaporate smoothly without
spurting and they can practically not be overheated. The NaHS04 may be used
in combination with either H2S04, HN03or HCI. However, the Mg(N03)2 can only
be used with HN03. The residue from NaHS04 is acidic and soluble in water.
8
However, it is recommended to take it up with an acid, which can even be
diluted, to impair the risk of hydrolysis. On the contrary, the residue from
Mg(NC>3)2 is alkaline, some MgO being always produced by the thermal
decomposition of Mg{N03)2. Therefore it is not soluble in water but it is soluble in
any acid. In general, Mg(N03)2 is only recommended when the presence of
sulphate is to be excluded. All Mg salts are very soluble.
When evaporating HCI04 solutions to dryness, LiClOa is a good evaporating
aid for pure tracer solutions [25], This reagent yields a practically transparent film
(melting point 236 °C), which is soluble in water, giving a neutral solution. The
residue must not be overheated, because it decomposes at about 430 °C,
yielding the strong alkaline U2O. which corrodes the glass beaker. The couple
HCIO4-UCIO4 is also useful for the transposition of chlorides to nitrates and vice
versa.
It is a safe practice when evaporating pure solutions of actinides to dryness to
take up the residue with a fairly concentrated acid such as 8 M HN03 and to heat
near the boiling temperature for a few minutes.
Sometimes, to eliminate the possibility of contamination by the laboratory
atmosphere, the evaporation is carried out in a closed chamber purged by clean
air or another gas. A simple device for this purpose may be built from a big glass
beaker with an inlet glass tube soldered perpendicularly to the wall and close to
the bottom. The beakers on the hot plate, containing the solutions to be
evaporated, are covered by the big beaker the bottom side up.
Rotary evaporators are only used in special cases.
2.3.3. Co lumn chromatography
Chromatography is a technique for the separation of a mixture of solutes. In
column chromatography the reagent is placed inside a column. Both ion
exchange (30, 31] and extraction chromatography with the resins from the
company Eichrom Industries [32] are used at the PSI laboratory. These
references contain general and specific information. In both techniques the
9
solution, which is the mobile phase, flows through the stationary phase (resin),
which is a solid, insoluble network containing the ionic groups capable of
exchange (ion exchange) or a liquid phase - containing the reagent - sorbed in
an inert support (extraction chromatography). The driving force for the separation
is the difference in the distribution of ions between the two phases.
Some particular technical features for an efficient chromatographic separation
are listed below:
1) The walls of the column have to be clean, so that the influent (the liquid
entering the column) flows down freely.
2) The resin bed is compacted by a slight pressure on the top and is free
of air bubbles.
3) The influent is always a clear solution. No turbid solutions are allowed
to enter the column. Small volume solutions may be filtered with a
syringe fitted with a filter.
4) Any influent is added when the preceding one has been completely
drained, that is drained to the bed top, usually covered with a filter.
5) After the sample solution has passed through the column, a wash
solution of the same composition as the sample solution is used to
eliminate the matrix elements not retained in the resin. This wash
solution is added first portion wise with a Pasteur pipette while washing
the rim of the column.
In this work, all solutions are passed through the column by gravity flow.
2.3.3.1. Separations with the anion exchanger BIO-RAD 1
The adsorption of the elements in this exchanger from HCI and HN03
solutions are displayed in Tables 1-4. This conventional, high capacity resin
allows the separation of many elements. Nearly always the selectivity depends
on complex-ion formation.
10
Table 1: Distribution coefficients of elements on a strong base anion exchange resin in HCI solutions. From K.A. Kraus and F. Nelson, Proceedings, Intern. Conference on Peaceful Uses of Atomic Energy, Vol. 7, pp. 113, 131, United Nations, 1956.
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.1
•J
. i . i
'.
Hr"
r
r
.A ' . 1
•
1 i
3
'
.
11
Table 2: Distribution coefficients of actinides and other metal ions on strong base anion
exchange resins in HCI solutions.
From J. Korkisch, Handbook of Ion Exchange Resins: Their Application to Inorganic Analytical
Chemistry, Vol 2, CRC Press, Boca Raton, FL, 1989, page 75.
Metal ion
Ac(IN) Th(IV) Pa(IV)
Pa(V)
U(VI)
u<iv) U(III) Nptlll)
Np(IV)
Np(V) NptVI) Pu(III)
Pu(IV) Pu(VI) Trivaleni \ irans-Pu > elements /
Teiravalent 1 Ti.Zr.Hf J
Cr(III) Mo(VI) W(V1) Mn(II) Fe(HI) Fe(ll) co<in Cu(II) Pb(II) Lanthanidcs + Y
1
M
• v *
-20 <l
( - ' - 2
l~2 <1
- ' \ < l
1<I —
<1
rf
*'
~1
4
2
-20 <l - 10 -10 -50 <l
- 1 --1
•-1 —
<l
-10
4
-100 <l -100 -180 -200 <l
- 2 • - 1
< l —2
<\
-100
Molarity of HCI
6 8
Nn ittwinxii^n — M A ^fHc^fT^fmn ,^^B^^KV M U i l U t\.}i J/l J U I I - ••
2 x 10' - 2 x 10" -100 -500 -500 - 1 0 ' -800 -10" -600 -800 - 1 - 5 0
-40 -300 - 2 0 -700 - 1 0 -700 -200 -800
10
id' -10* - 1 0 ' - 1 0 ' -600
>to:
-500 >I0 ' - 2 x W >I0 '
Strongly adsorbed from HCI > 6 M
-30 >I0* >IO' Strongly adsorbed from HCI >6 M
1 oiigni jusurpuun
No adsorption from HCI <8 M
Adsorbed from HCI > l M Adsorbed from HCI >1 M Adsorbed from HCI >9 M
>I0> >10* Adsorbed from HCI >7 M Adsorbed from HCI >6 M Adsorbed from HCI >3 M Adsorbed from HCI <6 M
No adsorption
>I0*
12
^ ^ > > — — _ ^ _ a w
W
>I0 ' - 1 0 ' -800 -300 >I0 ;
^ 9 w y
__
>I0 J
- 8 x 10' >KP
^ h r
>I0*
>
k
w
>10*
»
12
Table 3: Distribution coefficients of elements on a strong base anion exchange resin in HN03 solutions.
From J.P. Farisand R.F. Buchanan, Anion Exchange Characteristics of Element in Nitric Acid Medium, Anal. Chem. 36 (1964), pp. 1157-1158.
NO ADS n t i ' .
« g
NO ADS ; o.i i MOi -At t lT I HNOj
N O A O G . - no A 0 3 O * » T ) O N r o o t * O . M « *
» L . AOS. - B L t O - T ADSORPTION H O .
NO ACS.
1 S i IP
U I NO A OS.
S * I p'.
NO ADS. I NO AOS. N -• I JS
Co M-
SO ADS.
u <" - ' / .v M
' • ' r 2< Nt> sy ;:
9l_ ADS.
. ;;(,
« A 9
' Co '.T
TiT -,... AOS
sa I ' * : n o A O S . I NO AOS.
i Mf
r.O ADS.
1 « ' l
TO M " . c'(. ^N
HO T l
r r i _ . ADS.
-K: £ P Q ;
I n
_̂ r̂
T el
f O AOS
l I 1
•
T f
Ir-/ " 1 1
<
p
r
^ — s
^ c
/
—
Nd
• .L
u
-
'.1
—
-. 1-
n o AO . 1
'-. /
K
N
.-1 ei
| M
la NO AOS.
/(>C Hnr
/ E <•
j NO AOS.
F-; I s
NO AC
:nz "
1
» " » i i i
u » U |
Tb
l» p . ' "
1
-
MO AOS.
" 1 1 1?1
J _ J _
HO
1" NO AOS.
1 d
1
E>
" NO AOS.
F-n
Tm
i
1
v c
no ADS.
I n - ; No
U
1 1 i
1
13
Table 4: Distribution coefficients of actinides and other metal ions on strong base anion
exchange resins in HNO3 solutions.
From J. Korkisch, Handbook of Ion Exchange Resins: Their Application to Inorganic Analytical
Chemistry, Vol 2, CRC Press, Boca Raton, FL, 1989, Page 137.
Metal ion
Molarity of nitric acid
8 10 12 14
Ac(IIl) TTi(IV)
Pa(V) U(VI)
UflV) Np(IV) Np(V) Np(Vl) Np(III) Pu(IV)
Negligible or no adsorption
<1
- 2 <1
- 2 -50
< --100
~5 2
-16 ~ 6 - 3 <1
-16 -100
•300
50 216 323 20 140 200 50 200 300
- 1 2 - 3 0 - 5 0 - 7 - 1 2 - 1 6 - 3 - 6 - 6
5 10 - 1 0 -100 — — - 1 0 ' > I 0 ' >I0 1
Maximum K„ of about 15 in - 1 0 M HNO, Maximum Kd of about 15 in - 1 0 M HNO,
Negligible or no adsorption 10' > I 0 ' >10' >I0»
227 -100 - 5 1
-220 -40 -10
>IQ>
-20
- 1 0 ' 600
>10' —> -700
Pu(V|) Pu(III) Trivalem
trans-Pu elements
La(M> Ce(lll) Ce<ivy Prtiio Nd(III) Bi(UI) Hg(II) PWII) Pd(II) Au(IlI) Mo(Vl) z*iv> Hf(IV) Re<VH) Tc(VII)
<-
<-
Same behavior as Np(V[) or U(VI) Negligible or no adsorption
No adsorption
Maximum Kj of <10 in about 7 M HNO, Maximum Ka of <10 in about 6 M HNO, - 6 0 -200 -220 -100 Less strongly adsorbed than La — — — Very slight adsorption — — Maximum Ka of =50 in about 4 M HNO, Maximum K< of 10 in about 3 M HNO, Maximum K» of <10 in about 2 M HNO, Maximum K̂ of -100 in about 2 M HNO, Maximum Ka of >10* in about 1 M HNO, Maximum K« of >10 in 0.1 M HNO, Maximum K< of < 10 in about 6 M HNO,
• — — — — Slight adsorption — — — — -Maximum K* of -10* in 0.1 M HNO, Maximum Ka of > 10* in 0.1 M HNO,
In the presence of PbO- as a holding oxidant.1
14
From these tables it is evident that Pu may be separated from the major
elements of the lithosphere in both HNO3 and HCI solutions, the only exception
being Fe(lll) in HCI. However, HNO3 also shows a higher selectivity. Kressin and
Waterbury [33], in a comprehensive work, demonstrate the separation of 300
milligram of Pu(IV) from about 100 mg each of 45 elements in 7.2 M HNO3;
Pu(IV) was retained in the exchanger and the others were eluted. Then, Pu(IV)
was eluted with 0.36 M HCI 0.01 M HF.
The book by Korkisch listed many examples of Pu adsorption from HN03 and
other media, as well as its subsequent elution with diluted acids, complexing
agents for Pu(IV), or reducing agents by bringing Pu(IV) to Pu(lll) [34].
The Pu(IV) separation from HNO3 solutions was also the method selected by
the IAEA for the analysis of environmental materials [35] and by many other
workers.
The separation of Pu(IV) from HCI solutions, although rarely employed in the
analysis of environmental materials, may be useful in some cases. In 9 M HCI,
Fe(lll) and U(VI) are retained along with Pu(IV) giving an eluate devoid of these
elements, but with all the Th, Am, Cm. and the major elements of the lithosphere.
Talvitie claims that the retention of Pu(IV) is practically unaffected by a high
concentration in phosphate in the feed solution, which seems not to be the case
for separations in 8 M HN03 [36].
2.3.3.2. Separation of actinides from pure actinide solutions
Procedure:
1. Prepare a standard chromatographic column with BIO-RAD 1-X2 as
directed (cf paragraph 2.1). Pass 2 x 10 ml 8 M HNO3 to convert the
anion exchanger into the nitrate form. Discard the eluates.
Note. The last millilitres of effluent are free of chloride (AgNC>3 test).
2. Add into a 25 glass beaker the tracer as a nitrate in diluted HN03, 0.60
ml 1.00 M NaHS04, and 0.20 ml 18 M H2S04.
15
3. Evaporate the solution to dryness and calcine the residue on the hot
plate until no more white fumes evolve to eliminate the excess of
H2SO4. The residue is practically colourless and transparent when hot.
Note The treatment with NaHSOd and H2S04 ensures that both Pu and Np in the
feed solution are now in the (IV) oxidation state, independently of the oxidation state
in the tracer solution. Obviously, this treatment is superfluous if the Pu tracer solution
contains only Pu(IV) [8]. This treatment does not affect Am(lll). U(VI). Po(IV), and
Th(IV), but Np is brought to Np(IV).
4. Dissolve the cold residue in 0.20 ml water. Add 20 ml 8 M HNO3 and
mix well. This is the feed solution.
5. Pass the feed solution through the column from step 1 at a flow rate of
1-2 ml/min. Collect the eluate.
6. Wash the beaker with 8 M HNO3 and pass the solution through the
column. Collect the eluate. Note. The eluates from steps 5 and 6 contain the NaHSO« added in step 2.
7. Pass the appropriate solutions through the column at flow rates of 2-3
ml/min and collect the eluates.
The actinides in the eluates are electrodeposited as usual and measured by
alpha spectroscopy.
2.3.3.2.1. Discussion
The results of these separations -only one actinide each time- are
summarized in Table 5. Polonium is only electrodeposited to about 50% by the
method used.
It is evident that the proposed column enables a clear separation of Pu(IV)
and Np(IV) from Am, U, Po, and Th. All major crustal elements are not retained
at all and behave like Am (cf paragraph 2.3.3.1).
16
Table 5: Distribution of some actinides on BIO-RAD 1-X2.
Eluent.
sequential
Feed
Wash
Pu elution
Specials
Solution
8M HN03
8M HN03
10 M HCI
9MHCI0.1 MHI
0.10 M HCI 0.02 M HCI
1 M HCI 0.1 MHI Inventory
Nuclide Z43Am(lll) a *» U ( V| ) ^PoflV) 22STh(IV) 237Np(IV) 2d2Pu(IV)
Eluate Volume Nuclide
ml %
20 86
5 12.6 5 0.23 5 <0.05 5 <0.04
98.8
Volume Nuclide ml %
20 61.3
10 36.3 10 2.4 10 <0.02 10 <0.01
20 <0.03
20 <0.04
20 <0.01
104.8
Volume Nuclide ml %
20 34.8
10 17.5 10 1.6 10 <0.032
10 <0.031 10 0.061 10 <0.015
<0.024
20 <0.016
53.9
Volume Nuclide ml %
20 0.19
10 1.4 10 3.0 10 7.0 10 11.7
10 73.1 10 0.27 10 0.17
20 <0.15
97.1
Volume Nuclide ml %
20 0.16
10 0.11 10 <0.012 20 <0.011
10 0.21 10 1.4 10 2.9 10 8.5
20 67.6
20 16.0 96 9
Volume Nuclide ml %
33 0.011
5 0.002 5 <0.0003 5 O.0008
20 0.027 20 0.025
20 0.34 20 10
20 100.9 20 0.044
103.1
17
Experiments with Pu(VI) and U(VI) together in the feed solution have shown,
as expected from Tables 3 and 4, that both elements behave exactly in the same
way: they are eluted together with the feed solution and the 8 M HNO3 washings.
Chen et al. [37] found it necessary to add NaN02 to the 8 M HN03 and 12 M
HCI washing solutions to keep the Pu(IV) in the exchanger and prevent its
change in oxidation state and subsequent elution from the column. This
behaviour has never been observed in this laboratory after several years of
practice.
Campbell and Moss [38] state that, after washing the ion exchanger with 8 M
HNO3, it may stand for as long as 30 days without diminishing Pu recovery.
Hydroiodic acid (HI) was chosen for the reduction of Pu(IV) to Pu(lll) on the
exchanger because it is easily eliminated by volatilization.
From these results, a method for the separation of Pu(IV) from other elements
is detailed in the next paragraph.
2.3.3.3. Separation of Pu from other elements
This procedure is based on the last paragraph.
Procedure:
1. Prepare a standard chromatographic column with BIO-RAD 1-X2 as
directed (cf paragraph 2.1). Pass 2 x 10 ml 8 M HN03 to convert the
anion exchanger into the nitrate form. Discard the eluates.
Note. The last millilitres of effluent are free of chloride (AgN03 test).
2. Pass the feed solution at a flow rate of 1-2 ml/min. This solution has a
typical volume of 20 ml of 8 M HN03 and contains the Pu as Pu(IV).
Collect the eluate.
3. Wash the beaker which has contained the feed solution with 4 x 2.5 ml
8 M HNO3 and pass these washings individually through the column.
Use a Pasteur pipette for the transfer and wash carefully the rim of the
column. Collect these eluates together with that of step 2.
18
Note. These pooled eluates contain all the Am and the Cm from the feed solution,
practically all the U and a small fraction of the Th. Any Pu(lll, VI) and Np(V) are also
found here, as well as all major environmental elements.
4 . P a s s 2 0 m l 8 M H N 0 3 .
Note. This eluate contains some traces of the elements found in the eluates from
steps 2 and 3. Usually it is discarded.
5. P a s s 2 0 m M 0 M H C I .
Note. This eluate contains practically all the Th from the feed solution. The column is
now Th free. This step is mandatory even if the feed solution does not contain Th,
because it eliminates the nitric acid and converts the anion exchanger from the
nitrate form into the chloride form. Skipping this washing produces an extensive
oxidation of iodide to iodine in the next step.
6 . P a s s 2 0 m l 9 M HCI 0.10 M H I . T h e e l u a t e c o n t a i n s t he P u .
Note. This reagent must be prepared just before use by adding 0.30 ml 7.6 M HI to
20 ml 9 M HCI.
The eluates containing the Pu (step 6) and Th (step 5) may be treated as
usual for the electrodeposition of these elements (cf paragraph 2.3.4). The
pooled eluates from steps 2 and 3 have to be further processed to separate Am,
Cm, and U from the accompanying elements.
The method detailed above is very robust. Table 6 shows that even with a 1.0
g BIO-RAD 1-X2 column, 200 ml feed solution, and a flow rate of 5 ml/min >94%
of the Pu is retained in the column. In addition, the retained Pu may be
extensively washed with 10 M HCI without losses, as shown in Table 7. The
elution of Pu by 9 M HCI 0.10 M HI proceeds quantitatively (Table 8), leaving
behind a Pu free column.
Table 6: Pu(IV) retained on the anion exchangers from pure HN03 solutions.
Anion exchanger
type
1-X8 1-X8 1-X2 1-X2
Weigth as received
9 4.1 2.0 1.0 1.0
Feed solution
(8 M HN03)
ml 20 20 20 200
Flow rate feed solution
ml/min 1.3 2.3 5.0 5.0
Wash
(8 M HN03)
ml 44 30 30 25
Pu retained after passing the feed and
wash solutions %
>99.9 >99.9 >98 >94
19
Table 7: Pu(IV) retained on the anion exchangers after washing with 10 M HCI.
Anion exchanger
type
1-X8 1-X2 1-X2 1-X2
Weigth as received
9 4.1 6.2 2.0 1.0
Wash Flow rate Pu retained solution after passing
the wash solution ml ml/min % 100 1.2 >99 100 1.0 99.9 40 1.8 >99 20 3.4 99.5
Table 8: Pu(IV) eluted from the anion exchangers as Pu(lll) by 9 M HCI 0.10 M HI.
Anion exchanger
type
Weigth as received
9
Pu eluent Flow rate Pu eluted solution
ml ml/min % 1-X8 4.1 34 1.0 97-99 1-X2 6.2 30 1.0 >99 1-X2 4.0 20 1.8 98 1-X2 3.1 20 0.3 98-99 1-X2 2.0 20 2 - 3 >99.5 1-X2 1.0 20 4.2 >99.9
The BIO-RAD 1-X2 allows the separation of Pu(IV) from complex mixtures, as
shown in Table 9. Thus, the presence in the feed solution of the major
environmental elements do not impede a quantitative separation of Pu(IV). The
BIO-RAD 1-X2, because of its lower crosslinking, gives faster equilibrium rates
than BIO-RAD 1-X8, especially where large ions are concerned. For this reason,
it was preferred for further work. The Pu(IV) complex adsorbed on the exchanger
seems to be Pu(N03)62".
Hydrofluoric acid (Table 9, Exp. 10-13) suppresses the sorption of Pu(IV), but
the addition of H3BO3 demasks Pu(IV), probably by the reaction PuF62" + H3BO3
•* Pu(IV) + BF4\ allowing then its quantitative retention on the anion exchanger.
Phosphoric acid also masks Pu(IV) (Table 9, Exp. 14). This effect was
reported in the determination of Pu in bone [38]. No attempt was made to mask
the phosphate to liberate the Pu(IV).
20
Table 9: Separation of Pu(IV) on BIO-RAD 1-X2 from 8 M HN03 solutions containing
also other solutes.
Exp.
1
2
3
4
5
6
7
8
9
10 11 12
13
14
15 16 17
18 19
Exch. weight
9
1.0
1.0
1.0
1.0
1.0
1.0
1.0
2.0
2.0
2.0 2.0 2.0
2.0
2.0
1.0 2.0 2.0
2.0 2.0
Feed
volume
ml
5
5 16
20
20
20
20
20
20
20 20 40
40
20
36 115 115
88 97
composition (in addition to
8 M HN03)
0.08MNaHSO4
0.08MNaHSO4
0.43 M NaHSO*
0.47 M H2S04
0.92 M H2S04
2.3 M H2SOd
4.6 M H2S04
0.40 M H2C204
0.40 M H2C204
2 M NH4F 2.3 M HF
1.1 MHF +
+ 0.81 M H3BO3 2.3MHF +
+ 0.81 M H3BO3
2.2 M H3PO4
10 g "earth crust" 10 g "earth crust" 10 g "earth crust"
leachate 35 g soil leachate 33 g soil
flow rate
ml/min
2.9
2.8
4.9
5.2
4.5
3.3
2.1
2.3
1.8
NM 2.7 3.9
2.0
1.2
1.8 3.3 2.6
4.5 2.7
Pu in eluates
8 M HNO3
%
NM
NM
NM
3.5
10.7
52.9
93.7
<0.27
<0.17
NM 97.1 <0.21
<0.27
NM
NM NM NM
NM NM
9MHCI 0.10 M HI
%
100.4
98.4
96 1
96.0
90.5
46.1
5.8
95.4
97.6
1.7 1.5
98.1
96.1
5.2
99.0 97.8 98.9
95.8 98.9
Pu inventory
%
100.4
98.4
96.1
99.5
101.2
99.0
99.5
95.4
97.6
1.7 98.6 98.1
96.1
5.2
99.0 97.8 98.9
96.3 99.1
NM: not measured
21
2.3.3.4. Separation of Pu from Np
As shown in Tables 3 and 4, both Pu(IV) and Np(IV) have a high distribution
coefficient in 8 M HNO3, whereas Np(V) and Np(VI) have a low one similar to that
of Pu(VI) and U(VI). Thus, Pu(IV) and Np(IV) are retained together in the BIO-
RAD exchanger from 8 M HNO3 solutions, as shown in Table 5. This table shows
also that the elution of Pu from the exchanger by 9 M HCI - 0.1 M HI elutes also
about half of the Np, both being eluted in the (III) state.
To separate both actinides, the procedure given in paragraph 2.3.3.3. has
been modified as follows:
Steps 1-4 as above.
5. Pass 20 ml 12.2 M HCI.
6. Pass 20 ml 12.2 M HCI 0.10 M HI. The eluate contains the Pu (>99%)
and less than 0.5% of the Np.
Note. This reagent must be prepared just before use by adding 0.30 ml 7.6 M HI to
20 ml 12.2 M HCI.
7. Pass 40 ml 1 M HCI 0.10 M HI. The eluate contains the Np.
Note. This reagent must be prepared just before use by adding 0.60 ml 7.6 M HI to
40 ml 1 M HCI. The first 20 ml of the eluate contains about 80% of the Np.
By increasing the HCI concentration from 10 M to 12.2 M, the reduction of
Np(IV) to Np(lll), which is the eluted form, is avoided, whereas the reduction of
Pu(IV) to Pu(lll) is unaffected. The reduction (elution) of Np(IV) to Np(lll) by 1 M
HCI 0.1 M HI proceeds with moderate tailing.
This procedure allows the separation of both actinides when they are in the
(IV) state in the starting solution. When dealing with tracer solutions, Pu and Np
may be easily brought together to this state by heating with NaHS04 and H2S04
followed by a calcination of the residue [8]. For the detailed procedure see
paragraph 2.3.3.2, steps 2 and 3.
Several years old 237Np tracer solutions in 2 M HNO3 in this laboratory show a
Np(IV) content lower than 1%.
22
2.3.3.5. Anion exchanger regeneration
The standard chromatographic column after elution of Pu with 9 M HCI 0.10
M HI (cf paragraph 2.3.3.3, step 6) presents a red-black band in the top due to
b". The following procedure regenerates the anion exchanger in the chloride
form.
Pass consecutively the following solutions:
1. 20 ml 1 M HCI containing 200-500 mg Na2S03.
Note. The quantity needed of Na2S03 depends on the quantity of iodine fixed in the
column. At the end of the washing, the columns have to be bright yellow. The Na2S03
reduces the iodine to iodide, which in turn is fixed in the column. This solution also
elutes any Pu left behind in the column.
2. 20 ml 6 M HCI.
Note. The chloride displaces the iodide and the colour fades from bright yellow to the
original colour. The eluate may be tested for iodide by diluting with water and adding
some drops of 30% H202. A yellow-brown tint indicates iodine.
3. 20 ml water.
Note. The excess of HCI is washed out.
4. Close the stop-cock. Add about 10 ml water, take off, and discard the
filter on the top of the bed. Resuspend the exchanger with the help of a
stainless steel wire. Let to settle. Stop the column until the next use.
With the help of this regeneration cycle, BIO-RAD 1-X2 columns may be used
many times.
2.3.3.6. Anion exchanger stability
The capacity of several standard chromatographic columns (cf paragraph 2.1)
charged with 2.0 g BIO-RAD 1-X2 and used for routine work over several months
were determined. The following procedure was used:
1. Pass 20 ml 6 M HCI through the column and discard the eluate.
Note. This ensures that all the exchanger is in the chloride form.
2. Pass 2 x 20 ml water and discard the eluates.
Note. The excess of chloride is eliminated.
23
3. Pass 6 x 3 ml of a solution containing 50.0 mg NaNO^/ml. Collect the
eluates in a 250 ml Erlenmeyer.
Note. The chloride in the exchanger is fully replaced by the nitrate, which is in
excess. The affinity for nitrate is about 3 times higher than for chloride.
4. Dilute to 100 ml with water, add 6 ml of the N a N 0 3 solution and 2 ml of
a solution containing 60 mg N ^ C r C V m l . This solution is yellow.
Note. This NaN03 increases the salt content of the solution and thus helps in the
coagulation of the AgCI produced in the next step.
5. Titrate the chloride in this solution with an A g N 0 3 solution (29.5 mg
AgNCVml) . At the end point the solution turns from yellow to red
(Ag2Cr04 ) .
The titration of chloride with silver using Na2Cr04 as indicator is the so-called
Mohr method [40].
As shown in Table 10, the standard chromatographic columns may be
regenerated at least up to 42 times without loosing its original capacity. The
manufacturer certificate gives a capacity of 3.5 meq/g dry resin and a moisture
content (nominal) of 70-80% by weight. Table 10 shows a capacity of 1.2 meq/g
resin as received, which corresponds to an actual moisture content of 66%.
Table 10: Capacity of the exchanger BIO-RAD 1-X2 after many regeneration cycles
(standard chromatographic column).
Column number
1
2
3
4 4
Number of separations performed with the column
42
41
11
13 20
Capacity meq/column
2.24
2.38
2.39
2.48 2.44
Capacity normalized
to the original capacity
0.95
1.01
1.01
1.05 1.03
0(new) 2.36 =1.00
24
2.3.4. Electrodeposi t ion
Electrodeposition is a technique for the deposition of an element or a
compound as a thin layer onto a metallic disc. The actinides are deposited as
hydrated oxides. The electrodeposition is the last step of the separation process
before the measurement, usually alpha spectrometry. The electrodeposition
method for the actinides used in the PSI laboratory has been thoroughly
discussed elsewhere [6]. In addition, Np (237Np) -not included in the referred
paper- behaves like the other actinides.
Before the electrodeposition is performed, it is necessary to mineralize any
organic compounds present with the actinide as given in [6], paragraph "Sample
preparation for electrodeposition". The poor reproducibilities and recoveries
obtained in the electrodeposition of the actinides by some workers are probably
due to the presence of organic residues, which always accompany Th (eluted
with 9 M HCI + 5 M HCI from an Eichrom UTEVA resin) and Am-Cm (eluted with
the same reagents from an Eichrom TRU.Spec resin). The quantities of organic
residues eluted from the conventional anion exchangers like BIO-RAD 1 are
much smaller.
At present, the composition of the original electrolyte (0.10 M in NaHS04 and
0.53 M in Na2S04; pH 1.8) has been changed to 0.20 M in NaHS04 and 0.43 M
in Na2S04 (pH 1.5). This change has been introduced to take up the calcined
residue in 0.125 M NaHS04 instead of in water. Less than 0.02% of the actinides
are then left behind in the beaker used for the calcination. On the other side, this
higher acidity places the electrolyte composition in the middle of the plateau for
quantitative electrodeposition [6, Fig. 7]. Therefore the actual procedure is as
follows:
1. Obtain the calcined residue as directed in the two first paragraphs of
"Sample preparation for electrodeposition" [6].
2. Dissolve the residue in 1.80 ml 0.125 M NaHS04 and transfer this
solution into the electrolytic cell.
25
3. Wash the walls of the beaker three times with 1.00 ml of the 0.125 M
NaHS04 solution each time and transfer the washings into the
electrolytic cell.
4. Add into the electrolytic cell 1.00 ml 1.00 M NaHS04 and 4.20 ml 1.00
M Na2SOd.
5. Perform the electrolysis as directed: 1.20 A for 60 min [6].
Under these conditions and with the equipment used, the voltage drops from
about 8.5 V at the beginning to 5.4 V at the end of the electrodeposition. This
tension fall corresponds to the increase in the temperature of the electrolyte.
The calibration of the alpha spectrometer has been described elsewhere [5].
2.3.4.1. Cleaning of the components of the electrolytic cell
Although the electrodeposition procedure used is essentially quantitative, with
the exception of microgram quantities of Th [6], it would be necessary to clean
the components of the electrolytic cells when processing consecutively samples
whose activities differ in several orders of magnitude.
Proceed as follows: Place the electrolytic cell components (anode,
polypropylene funnel, polyethylene scintillation vial, cap, and planchet holder) in
a glass beaker. Add enough cleaning solution C to cover the components. Boil
for 30 min while keeping the components covered by the solution. Discard the
solution and rinse the components with water. Set aside for drying.
The cleaning efficiency was tested by electrodepositing several 232Th {0.036
mg; 147 mBq) replicates. The electrodeposition yields were in the range 23-37%.
After use, the components were rinsed with water and employed again for the
electrodeposition of blank solutions. About 1-2% of the original added 232Th was
found in the blank planchets. All the components in contact with the electrolyte
(anode, polypropylene funnel, polyethylene scintillation vial) were contaminated.
But when the components were rinsed with water and then washed by the
proposed procedure, no 232Th (<0.02%) was found in the blank discs.
26
Probable that at the end of the electrodeposition the Th still in solution is
precipitated as the hydroxide, which adheres to the surface of the components.
This hydroxide is dissolved by the acid in the new electrolyte (contamination) or
in the cleaning solution C (decontamination).
No contamination has been observed with the other actinides by this
mechanism because their electrodeposition is essentially quantitative. On the
other hand, hot 0.10 M H2C2O4 (cleaning solution C) dissolves the actinides
electrodeposited in the stainless steel planchets (cf paragraph 2.3.4.2). Thus,
cleaning solution C is an effective decontamination agent.
Oxalic acid is a relatively strong acid (pKi 1.27; pK2 4.27); the 0.10 M solution
has a pH of 1.2. It is also a strong complexing agent for most actinides and a
mild reductant. For all these reasons, the different components of the electrolytic
cell, which are made in materials such as plastic (funnel, scintillation vial, and
cap), platine (anode), and stainless steal (planchet holder) may be
decontaminated together in the same cleaning solution without deterioration. The
acid resistant stainless steel 316 L (DIN 1.4435) is recommended for the making
of the planchet holder. The polyethylene scintillation vial is used once only.
2.3.4.2. Etching of the actinides electrodeposited on the planchets
Sometimes, especially when developing radiochemical methods, the electro
deposited source shows the presence of interfering nuclides. In other cases, the
source is radiochemical^ pure, but the resolution of the alpha spectrum is
degraded due to the codeposition of inactive extraneous material. In all these
cases, the simplest way to solve the problems are to dissolve (etching) the
electrodeposited layer. This provides a solution for further processing.
To simplify this process, it is desirable that the reagent used for etching does
not attack the stainless steel planchet while dissolving quantitatively the
electrodeposited layer. For this reason HCI has to be excluded.
The methods employed for etching are displayed in Table 11. The procedure
is as follows;
27
1. Place a Teflon rod (5 mm of diameter) fitting in the bottom of a 25 ml
glass beaker.
Note. The Teflon rod, which fits exactly into the bottom of the beaker, helps to keep
the planchet in a near upright position during the etching and helps to remove it later
in step 6.
2. Place the planchet in the beaker, the radioactive side up.
3. Add the etching reagent and cover the beaker with a watch glass.
4. Heat as directed in Table 11.
5. Cool the beaker in a water bath.
6. Remove the planchet with an acid resistant tong and rinse with some
drops of fresh reagent while collecting the washings in the beaker.
Keep this solution for further processing.
7. Wash the planchet successively with water and 0.13 M NH4OH and
discard the washings.
8. Dry the planchet under an infrared lamp.
9. Measure the planchet in an alpha spectrometer to verify the quanti
tative removing of the nuclides.
Table 11: Reagents and conditions used for etching the nuclides from the planchets.
Method
NA-1
NA-2
NA-3
NA-4
CA
SU-1
SU-2
SU-3
Reagent
HN03
HNO3
HNO3
HN03
Na2C03
NaHS04
NaHS04
NaHS04
Concentration M
14.4
14.4
7.2
7.2
1
1
0.12
0.12
Volume ml
5
5 5 5
15
5
5 10
Time mm
4 20 10 30
30
10
10 30
Temperature
Near the boiling point
Near the boiling point
Near the boiling point
Near the boiling point
Boiling
Simmering
Simmering
Simmering
OX-1 NH4HC204 0.1 10 30 Simmering OX-2 H2C204 0.1 10 10 Simmering OX-3 H2C2Q4 0J 10 30 Simmering
28
The results obtained with several reagents are presented in Table 12. The 228Th generated in the planchet from the decay of 232U is implanted in the steel
because of its high recoil energy. Therefore, it needs stronger conditions (NA-2)
to be etched than the nuclides deposited onto the planchet {NA-1). Polonium is
only partially etched.
Table 12: Nuclides remaining in the planchets after etching.
Method Nuclide [%] 2M.238JJ 228.230.232^ 2 2 8 ^ 239.240pu 2 4 1 . 2 4 3 ^ 2 4 2 . 2 4 4 ^ 2 3 7 N p 210pQ
232U (1) ^ P u 2 < ; L ' Pu
NA-1 NA-2 NA-3 NA-4
<0.5 <0.2 <0.2
<0.5 <0.2 <0.2
10-26 <0.2
<4 <0.5 <0.5 <0.5
<0.5
<0.5 <0.5
<0.5 <0.5
10-40
CA <1 1 - 90 50 20
SU-1 SU-2 SU-3
OX-1 OX-2 OX-3
<0.2 <0.2
<1 <0.1
<0.2 <0.2 - 3
<0.5 <0.1
40 19-36 5-11
2 - 4
1 -2 1
<0.3 <0.5 <5
<0.8 40 - 80
(1) 228Th generated in the planchet from the decay of 232U.
The planchets used have a weight of 250 mg. Usually less than 1 mg is
dissolved by any of the methods listed in Table 11.
Plutonium etched by the methods NA-1. NA-3, and OX-2 is in the (IV)
oxidation state. Therefore, these solutions may be brought to 8 M HNO3 and feed
directly into the BIO-RAD exchanger for purification without Pu losses, as was
tested with 14 Pu planchets contaminated with 228Th and etched by the NA-3
method. The mean Pu recovery of the whole process (etching - Pu separation in
BIO-RAD - electrodeposition) was 96.6% (median 96.5%) with recoveries
ranging from 89.4% to 102.7%.
29
2.3.5. Isotopic exchange between sample and tracer
The nuclides 236Pu or 242Pu are usually used as tracers to measure the
chemical yield of Pu isolation procedures for the determination of 238Pu, 239Pu
and 240Pu. The foundation of any yield-tracer method in radiochemistry is that the
activity ratio of the nuclide to be determined to that of the tracer added is the
same in the original sample and in the isolated fraction. In our case, the ideal
solution is to bring all Pu isotopes in the sample solution to Pu(IV) before feeding
the ion exchanger BIO-RAD 1-X2, because only Pu(IV) is quantitatively retained
by this exchanger.
We failed to bring Pu to Pu(IV) in 8 M HN03 leachates from soils and
mineralized faeces with the widespread NaN02. Furthermore, no isotopic
exchange between sample and tracer took place. But Pu determinations in which
the 8 M HN03 leachates were treated with H202 showed a very good
reproducibility, although the yields were somewhat dispersed.
To investigate the isotopic exchange in the system HNO3-H2O2, the following
procedure was applied: Ten ml HN03 in a tall glass beaker was spiked with 242Pu
(Pu(IV), 0.500 ml, 70 mBq, 0.10 M NaHS04) and 239Pu (33% Pu(lV) and 67%
Pu(VI), 0.100 ml, 200 mBq, 1 M HNO3). Thirty percent H202 was added and the
beaker was covered with a watch-glass. The solution was simmered for some
minutes. On occasions the addition of H202 and the subsequent boiling were
repeated. After cooling and adjusting the HNO3 concentration to 8 M when
necessary, the solution was feed into the BIO-RAD standard column. Two
fractions were collected for the determination of Pu: the 8 M HNO3 eluates (feed
and washing) and the HCI + HI eluate; the first one contains the Pu(VI), the
second the Pu(IV) in the feed solution.
30
Table 13: Isotopic exchange 242Pu(IV) - 239Pu(IV, VI) in the system H N 0 3 - H 2 0 2 .
Exper.
A B C D
E F
Isotopic exchange conditions
HNO, cone.
M
8
8 8 8
8 8
H202 Boiling (30%) time
ml min
2x0.10 2x5 2x0.10 2x5
2x0.10 (a) 2x5 nil 15
0.20 19 h (b) 0.20 2.8 d (b)
Pu recoveries (inventory)
242Pu
%
97.8 99.7 98.4 97.2
97.4
c)
239Pu
%
99.3 99.5 100.3 99.5
98.0
c)
242Pu
recovered
as Pu(IV)
%
94.0 95.6 69.2 99.8
83.4 72.6
Isotopic ratio 239Pu/242Pu,
activities
Added
2.88 2.85 2.85 2.85
3.01 2.86
Recovered as Pu(IV)
2.92 2.84 2.90 1.01
3.01 2.88
Ratio add. / recov.
0.98 1.01 0.98 2.84
1.00 0.99
8(d) 1.00 c) O 55. 2.84 2.87 0.99
H I J K
L
3 3 3 3
14.4
0.10 0.10 0.10 0.10
3x0.10
15 15 15 15
3x3
(e)
(0 (e)
(fl
(g)
98.2 99.8 101.1 101.4
99.2
100.1 101.2 102.1 100.8
98.4
79.3 77.9 83.4 77.2
34.9
2.83 2.84 2.35 2.37
2.38
2.83 2.85 2.33 2.31
2.32
1.00 1.00 1.01 1.03
1.03
(a) 0.29 mmols NaN02 dissolved in 0.20 ml water was added before each H2O2 addition. (b) No boiling. Waiting time at room temperature. (c) Pu was not determined in the 8 M HNO3 etuates (d) Hundred ml ot soil leachate (30 g dry ashed soil was leached with 100 ml boiling 8 M HNO3) (e) After boiling the 3 M HNO3 solution for 15 min. 1 ml water and 9 ml 14.4 M HNO3 were added to obtain a solution 8 M in HNO3. It was boiled for 2 min. and set aside for cooling. Then. 0.58 mmols NaN02 dissolved in 0.20 ml water was added. After 30 min of waiting time, the separation was performed as usual. (0 After boiling the 3 M HNO3 solution for 15 min, 1 ml water and 9 ml 14.4 M HNO3 were added to obtain a solution 8 M in HNO3. It was boiled for 2 min, and then set aside for cooling. The separation was performed as usual. (g) Before performing the separation, the solution was diluted wrth 8 ml water to obtain a solution 8 M in HNO3.
31
The results are shown in Table 13. It is evident that isotopic equilibrium is
attained (ratio added/recovered = 1) under very large experimental conditions.
No attainment is possible without H2O2 (Exp. D), in which case all the 242Pu is
recovered as Pu(IV). The attainment is also possible at room temperature (Exp.
E and F) and in 100 ml of soil leachate (Exp. G). Probably the attainment goes
through a temporary passage by the Pu(V) state [39]. In some cases (Exp. H and
J), NaN02 was added in a failed attempt to increase the yield of Pu(IV).
The reagent H202 decomposes in boiling HN03. To follow this decomposition,
H2O2 (0.50 ml, 30%) and Mo(VI) (4.0 mg) were added to 20 ml HNO3 and the
solution was boiled. Mo(VI) forms a yellow complex with H202. This colour
disappears along with the decomposition of H2O2. Thus, in 8 M HNO3 the colour
vanishes in 4 minutes, but needs 18 minutes in 5 M and 2 hours in 3 M.
3 . A p p l i c a t i o n s
3 . 1 . Purif ication of tracer solut ions
Sometimes it is necessary to purify the tracer solutions used for yield
determination. Typical examples are:
• 242Pu tracer. Contaminant: 241Pu. which decays in 241Am; and
• 236Pu tracer. Contaminant: its daughter 232U, which decays in 228Th.
To carry on this purification follow the steps 1 to 4 in the procedure given
above (cf paragraph 2.3.3.2) and continue so:
5. Wash the beaker 4 times with 2.5 ml 8 M HN03 each time and add
these washings individually into the column. Discard the eluates.
6. Pass 20 ml 8 M HNO3 through the column. Discard the eluate.
7. Pass 20 ml 10 M HCI through the column. Discard the eluate.
8. Pass 20 ml 9 M HCI 0.10 M HI through the column. This eluate
contains the purified Pu as Pu(lll).
To prepare the new Pu tracer solution, here are two possibilities:
32
1. If a Pu(IV) solution in 0.1 M NaHS04 is preferred, collect the eluate of
step 8 from the preceding paragraph in a beaker containing 0.60 ml 1.0
M NaHS04 and 0.40 ml 18 M H2S04. Both reagents are added before
the eluate. Then, proceed following the procedure given in [8] under
"Preparation of a Pu(IV) solution in 0.10 M NaHS04".
2. If the presence of NaHS04 in the new Pu tracer solution is not desired,
proceed as follows: Evaporate to dryness the eluate from step 8 above.
Add 1-2 ml 14 M HN03 and evaporate again to dryness. Repeat this
step so many times as necessary to eliminate the iodine. Add 2-3 ml 8
M HN03, cover the beaker with a glass-watch, and heat for several
minutes to bring the Pu in solution. Let the beaker cool to room
temperature and dilute with HN03 to get the desired Pu concentration
and a HN03 concentration of about 2 M. The oxidation state of Pu in
this solution is mostly Pu(IV).
The Pu concentration in the new solution may be calculated from the aliquot
taken from the original solution. For precise work a new standardization must be
performed via electrodeposition [6].
3.2. Determination of actinides in primary coolant reactor water
In chemistry, primary coolant reactor water in a boiling water reactor (BWR) is
a solution of carrier free radioactive isotopes in pure water. In a pressurized
water reactor (PWR) this solution also contains boron. 10B is added as neutron
absorber.
Because there is no interfering matrix in water from a BWR, the actinides may
be directly electrodeposited without chemical separation. In the case of the PWR
the actinides have to be separated from the boron. This may be easily done by
selective volatilization of boron as methyl borate (B(OCH3)3) or as boron fluoride
(BF3).
33
Procedure:
1. Transfer the water aliquot into the appropriate tared glass beaker. Add
enough H N 0 3 to obtain at least a 0.1 M solution.
Note. The water sample has to be acidified in situ with HN03 immediately after
collection to get a pH 2 or lower.
2. Evaporate the solution to dryness while keeping the solution under the
boiling temperature.
3. The residue must be weightless and barely visible (BWR water).
Note. In the case of PWR water a white residue is obtained. The simplest way to get
rid of the boron is to moisten the residue with methanol in order to get a fluid
suspension. Then, evaporate to dryness without boiling (BP methanol 65 °C). Repeat
this treatment so many times as necessary (usually 2 to 3 times) to obtain a
weightless residue.
4. Add into the beaker 0.600 ml 1.0 M NaHS0 4 . 0.500 ml 9 8 % H 2 S 0 4 and
enough 8 M H N 0 3 to cover the bottom of the beaker.
5. Cover with a glass watch and heat to wash the beaker walls with the
refluxing acid for several minutes.
6. Remove the glass watch and evaporate the solution under the boiling
temperature. When the white fumes evolve, increase the temperature
and finally calcine the residue until no more white fumes evolve.
7. Treat this residue as usual for the electrodeposition of the actinides.
Note. If the alpha spectrum of the electrodeposited sample shows a peak at 5.49
MeV. the sample contains 24,Am and/or 238Pu. To separate these elements, a new
aliquot has to be processed through steps 1 to 6 and the residue dissolved in about
10 ml of 8 M HNO3. This solution is fed into a BIO-RAD 1-X2 standard
chromatographic column and Am and Cm are separated from Pu as usual (cf
paragraph 2.3.3.3 and Table 5).
No tracers for monitoring the recovery of the actinides are needed, since the
operations involved work quantitatively.
3 . 2 . 1 . R e s u l t s
The results of the determinations are shown in Table 14. These analyses
were spread over 5 years.
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35
In one case (sample 5 in Table 14), the water aliquot was poured in a teflon
evaporating dish containing 0.60 ml 1.0 M NaHS04 and 20 ml 23 M HF. The
solution was evaporated to dryness. The white residue was evaporated again to
dryness, first in the presence of 5 ml 23 M HF and finally with 5 ml 8 M HN03.
The residual white bead was transferred into a glass beaker with 8 M HNO3. After
addition of 0.20 ml 18 M H2SO4, the solution was evaporated and calcined as
usual for the electrodeposition of the actinides. The result shows that the
actinides in the water sample do not need a HF treatment.
3.3. Determination of Pu in concrete
Concrete is used for proton and neutron shielding purposes in PSI. The
thermalized neutrons activate the 23aU -typically 1 j.ig/g concrete equivalent to 12
mBq-, producing eventually 239Pu and 240Pu. The concentration of these Pu
nuclides has to be known before the disposal of the concrete.
3 .3 .1 . Samp le dissolut ion
Procedure:
1. The starting material is about 1 g of the fine grinded concrete.
2. Place the sample dispersed as a fine layer in a platinum evaporating
dish.
Note. A platinum dish with a diameter of 5-6 cm in the bottom may be used.
3. Introduce the vessel for 20 min in a preheated oven at 700 °C.
Note. This calcination mineralizes completely the organic matter invariably found in
concrete. Moreover, the concrete is sintered at this temperature. To minimize the size
of these black sintered particles, which are more resistant to HF attack than the
original powder, the concrete is dispersed as a fine layer in step 2.
This step produces a weight loss of about 15%, which corresponds mostly to the C02
volatilized from the decomposition of the carbonates.
4. Transfer the cold residue into a Teflon evaporating dish. Use a water
jet to transfer the last fine particles.
36
5. Add the Pu tracer to the moist residue in the Teflon dish, as well as
any tracers needed for the determination of other nuclides.
6. Add 4 0 % HF. dropwise at the beginning, until a total volume of at least
5 ml. Evaporate to dryness on a hot plate while keeping the solution
under the boiling temperature to avoid sputtering.
7. Repeat step 6 twice.
Note. The HF attacks the silicates and produces several insoluble simple and mixed
fluorides. When evaporated to dryness, Si is volatilized as SiF*. After 3 additions of
HF, the weight of the white residue left behind stays constant. This weight is about
65% of that of the calcined concrete.
If especially resistant Pu bearing compounds are expected, the first HF attack may
be carried out in a steel bomb with Teflon lining. A simple bomb such as introduced
by Bernas [41] can withstand even 200 °C for 3 days when half filled with 40% HF in
addition to the silicate sample. The resulting slurry is then transferred to a Teflon
evaporating dish to volatilize the Si.
8. Add 0.30 g H 3 B 0 3 and 5 ml 7.2 M HN0 3 . Evaporate to dryness as
usual.
9. Add 5 ml 7.2 M HN0 3 . Evaporate to dryness as usual.
Note. The residue leaving step 7 is a mixture of simple and mixed fluorides, which
also contains a small fraction of the original Si, probably a fluosilicate. This residual
Si cannot be volatilized by evaporations with HF.
To obtain a clear solution in nitric acid, which is the starting solution for most
separation methods, the presence of H3B03 is mandatory. Thus. H3B03 reacts with
the fluorides and forms the fluoborates (BF4), which are soluble in HN03. Let us
assume that all the residue leaving step 7 is fluorine, it would be necessary 0.81
times its weight of H3B03 to form the BF4". About 0.5 times is enough.
10. Repeat step 9.
1 1 . Dissolve the residue in the appropriate solvent depending on the Pu
separation method to be used.
37
3.3.2. Preparation of the solution for the separation of Pu
Procedure:
1. Transfer the residue (preceding paragraph, step 10) into a 50 ml tall
glass beaker with the help of 4 x 5 ml 8 M HNO3. Cover the beaker
with a watch glass.
2. Heat to dissolve. Boil a few minutes. Let the solution cool for a few
minutes.
3. Add 0.20 ml 30% H202. Mix and simmer for 5 min.
4. Repeat step 3.
Note. Steps 3 and 4 ensure the Pu isotopic equilibrium between sample and tracer
(cf paragraph 2.3.5). Moreover, any Mn(IV) oxides, formed from the decomposition of
Mn(N03)2 during the evaporations steps 9 and 10 in the preceding paragraph, and
which are insoluble in HN03, are reduced to Mn(ll) and so brought readily into
solution. An intense yellow-orange colour develops with the addition of H202. This is
due to the formation of a Ti-H?02 complex. The colour fades down completely during
the simmering because of the decomposition of H202. Hydrogen peroxide
decomposes readily in warm 8 M HN03. and the decomposition is accelerated by
metallic ions such as Fe(lll).
5. Let cool down the solution. This 20 ml 8 M H N 0 3 solution is the feed
solution for the separation of Pu.
Note. Filter before feed the column if necessary. A 0.45 urn filler adapted to a syringe
is very convenient.
3.3.3. Separation of Pu on BIO-RAD 1-X2
The procedure is that given above for the separation of Pu from other
elements {cf paragraph 2.3.3.3).
3.3.4. Results
Six samples of a concrete block employed for shielding a proton beam in PSI
were analyzed to determine their 239240pu and 238U contents. A drilling core was
38
taken from the concrete block along the beam direction. Five samples were
extracted from the core at regular distances of 0 cm (the concrete surface) to 20
cm. In addition, another sample was taken (blank) outside from the beam path.
The determination of 238U was made in the 8 M HN03 eluates of the BIO-RAD
1-X2 column. The U was separated on an Eichrom UTEVA column. The
recoveries of the added tracers were about 70% (242Pu) and 90% (232U).
The results are shown in Table 15. The ratio 239-240pu/238U decreases linearly
with the depth in the concrete shielding [42].
Table 15: Determination of 239240Pu and 23SU in shielding concrete.
Sampling depth
cm
0 5
10 15 20
Content,
239.240pu
32.4 30.7 11.9 12.3 5.66
mBq/sample
2 3 8 u
13.1 14.7 8.19 12.9 14.7
239.240p u / 238 U
ratio
2.47 2.09 1.45 0.95 0.39
blank <0.18 8.24 <0.02
3.4. Determination of Pu in air filters
Air filters are employed for monitoring actinides in aerosols of exposed areas.
The ambient air is continuously forced through a filter with the help of a vacuum
pump. The aerosols are retained on the filter. The total alpha activity in the filter
is measured continuously or from time to time. Filters with activities over a given
threshold are subsequently assayed by alpha spectrometry. When necessary,
the aerosol -with or without the filter- is brought in solution and the actinides are
separated from the other elements.
When the composition of the liberated aerosol is known, it is possible to apply
directly the appropriate dissolution method for the actinides. This information is
also useful later for the analysis of faeces from the workers present in the
39
exposed area. Thus, if the Pu on the filter can be brought into solution by
leaching with HNO3, it must be also the same for the Pu in the faeces. However,
if the Pu on the filter needs a total dissolution method, any residue left after
leaching the faeces with HNO3 must also be treated in the same way to bring all
the Pu into solution.
These filters are fabricated with borosilicate glass fibre and contain no binder
or cellulose. The 27 mm in diameter Whatman GF/A filter (30 mg, 5.2 mg/cm2) is
commonly used. It remains unaltered after heating up to 500°C. The Whatman
GF/B filter is thicker than the A filter (14 mg/cm2).
As received in the laboratory, the filters are more or less black on the
exposed side, depending on the dust collected, which is a mixture of organic
(fabrics, skin, hairs, etc) and inorganic matter (mostly soot and soil particles).
Some methods, to bring the actinides deposited on microfibre glass filters into
solution, are displayed on Table 16. The detailed procedures for methods B (cf
paragraphs 3.4.1 and 3.4.1.1) and C (cf paragraphs 3.4.1 and 3.4.1.2) are given
below.
40
Table 16: Some possibilities for dissolution of actinides from aerosols deposited on
microfibre glass filters.
Method
A
B
C
D
E
F
G
H
Dry or wet ashing
OPEN VESSEL Dry ashing , (500°C, <15min)
Wet ashing
CLOSED VESSEL
Wet ashing
Total dissolution or leaching (1)
i\sh Total diss.
Leaching
Total diss.
— Leaching
Total diss.
— Leaching
(3)
First step
HF
8 M HN03
HF + HNO3 + HCIO4
HNO3 + H2S04 (2)
HF + 14 M HNO3
14 M HNO3
Second step
HCIO* or H3BO3 + 8 M HNO3
—
—
—
HCIO4 or H3BO3 + 8 M HNO3
—
(1) .Total1' means aerosol and filter. .Leaching" means to bring into solution the actinides but not the filter. (2) This leaching may be carried out with the apparatus given in reference [44J. (3) Microwave heating or conventional oven in the 1st step. Open vessel in the 2nd step.
3.4.1. Dry ashing of the deposit
Procedure:
1. Place the filter on a wire mesh, the aerosol side up.
2. Introduce the mesh in an oven at 500° C for several minutes.
Note. The mesh facilitates the air circulation around the filter and accelerates the
ashing of the dust. Also useful is to place the mesh not in the bottom of the oven but
on an aluminium strip bent to form an U. Usually a pure white filter is obtained in less
than 15 min.
The mineralized filter is now ready for total dissolution (cf below paragraph
3.4.1.1) or for leaching (cf below paragraph 3.4.1.2).
41
3.4.1.1. Total dissolution
Procedure:
1. Place the dry ashed filter in a Teflon dish of the appropriate size.
2. Wet with some drops of water and then add Pu tracer and other tracers
when necessary.
3. Add 4 0 % HF on the filter and evaporate to dryness on a hot plate.
Note. The filter disintegrates on adding the HF. About 0.5 ml HF is enough.
4. Repeat twice the step 3.
Note. The weight of the dry white residue is about 50% of that of the original virgin
filter. Further evaporations with HF do not reduce the weight of the residue, which
means that all the Si that can be volatilized with HF has been now evaporated. A
small fraction of the original Si remains, probably a fluosilicate. The major elements in
the residue are Al, Ca, Mg, K, and Na.
5. Add 15 mg H3BO3 dissolved in 1 ml water and 1 ml 8 M HN03 to the
residue and evaporate to dryness.
6. Add 1 ml 8 M HN03 and evaporate to dryness.
7. Repeat step 6.
Note. Boric acid is added in step 5 for safety reasons to complex any remaining
fluoride as BF4" <cf paragraph 2.3.3.3 and Table 9 for Pu(IV) complexing by HF).
Actually, the residue after step 7 is always soluble in 2-8 M HN03 even without
adding H3B03 in step 5.
8. Dissolve the residue in the appropriate solvent depending on the Pu
separation method to be used.
3.4.1.1.1. Preparation of the solution for the separation of Pu
Procedure:
1. Transfer the residue (preceding paragraph, step 7) into a 50 ml tall
glass beaker with the help of 4 x 5 ml 8 M HN03. Cover the beaker
with a watch glass.
2. Heat to dissolve. Boil a few minutes. Let the solution cool somewhat.
42
3. Add 0.20 ml 30% H202. Mix and simmer for 5 min.
4. Repeat step 3. Let the solution cool.
3.4.1.1.2. Separation of Pu on BIO-RAD 1-X2
The procedure is that given above for the separation of Pu from other elements
(cf paragraph 2.3.3.3).
3.4.1.1.3. Results
Two samples were tested. Each sample consists of a set of 4 filters weighing
120 mg from the waste incinerator plant (now dismantled) of PSI. Each sample
was spiked with 242Pu(IV) in 0.1 M NaHS04 and they were processed following
the procedure given above (cf paragraphs 3.4.1 - 3.4.1.1.2). No H3B03 was
added. The separated Pu fractions yielded a recovery of 82.7% and 94.7%. No 239'240Pu was detected. The discarded 8 M HN03 and 10 M HCI washings
contained the natural U and Th isotopes.
Two other filters spiked with 242Pu in 2 M HN03 (99% Pu(IV)) were dissolved
following method D (cf Table 16). The dry perchlorate residues were dissolved
and treated as in paragraph 3.4.1.1.1 and 3.4.1.1.2. The 242Pu recoveries were
87.6% and 93.1%.
No real Pu bearing filters have been analyzed until today.
3.4.1.2. Leaching
This operation brings the actinides into solution. It corresponds to method C
in Table 16.
Procedure:
1. Cut the dry ashed filter in several parts and place them into a 50 ml
volumetric flask. Add Pu tracer -and any other necessary tracers-. 20
ml 8 M HN03 l and 0.20 ml 30% H202. Adapt an air condenser (50 cm
long) to the volumetric flask.
43
2. Boil for 30 min under total reflux. Let the solution to cool somewhat.
3. Add 0.20 ml 30% H202. Resume boiling for 5 min.
4. Bring the solution to room temperature.
Note. The glass fibre filter is not attacked during the leaching, but its structure is
destroyed and the fibres dispersed.
5. Filter the solution through a 27 mm diameter Whatman GF/A filter.
6. Wash the volumetric flask with 5 ml 8 M HNO3 and then the filter.
Collect the filtrate with the main solution.
7. Repeat step 6.
8. This solution is ready for the Pu separation on BIO-RAD 1-X2.
9. If necessary, the filter is treated as in Total dissolution (cf paragraph
3.4.1.1). Note. If the Pu tracer added in step 1 was 242Pu, it is necessary to add now Z3flPu,
and vice versa. Thus, it is possible to distinguish, if any ^Pu or 239240pu is found in
this fraction, between the Pu-insoluble in 8 M HNO3 and that carried over inevitably
by the leachate.
The Pu in the leachate (step 8) is processed as usual for the separation of Pu
(cf paragraph 2.3.3.3).
3.5. Determination of Pu in faeces
The analysis of faeces for the determination of actinides is carried out in PSI
only following an accident, not as a routine task. The results of these analyses
are needed for the calculation of the committed dose [43].
3 .5 .1 . Sample col lect ion
Procedure:
1. The person under investigation collects the faeces in the bottom of a
polyethylene bag (20x30 cm; weight 1.2 g). The bag is then closed with
a knot (nylon rope) as close to the faeces as possible.
Note. The polyethylene bag and the nylon rope are ashless.
44
2. On arrival at the laboratory, the samples are weighed and then frozen.
3 .5 .2 . Mineral izat ion
3.5.2.1. Mineralization of the bulk of the samples by dry ashing
Faeces contain a lot of water. Therefore, they need to be heated stepwise,
first to dry the sample and then to mineralize it.
Procedure:
1. Weigh an aluminium form of the appropriate size as those used for
household baking. Cover the bottom of the form with a sheet of baking
paper.
2. Place the frozen sample on the form, cut and discard the part of the
bag above the knot.
3. Introduce the sample in a cold oven. Set the temperature at 200 °C.
Keep for at least 5 h {ideally overnight) at this temperature
Note. During this step, the sample shrinks; the polyethylene melts and covers the
sample with a film, producing finally an odourless and partially charred ball, weighing
about 30% of the fresh weight.
The baking paper retains any liquid produced at the beginning of the heating. This
liquid is evaporated on the paper, thus avoiding a reaction with the aluminium.
4 . Increase the oven temperature up to 250 °C. Keep for at least 5 h at
this temperature.
5. Increase the oven temperature up to 500 °C. Keep for at least 5 h
(ideally overnight) at this temperature.
Note. The colour of the ash is normally medium grey, but may vary from black-brown
to whitish, depending on the content of Fe and carbon. A carbon free ash is
practically never obtained at this temperature.
6. Weigh the aluminium form with the ash.
Note. The weight of the ash is about 4% of that of the fresh faeces.
45
3.5.2.2. F in ish ing by we t ash ing
This operation mineralizes the last carbon particles.
Procedure:
1. Transfer the ash from the aluminium form into a taped (14/23) and
tared volumetric flask. Use a 50 ml flask (up to 3 g ash) or a 100 ml
flask (3-6 gash ) .
2 . Add Pu tracer as well as other tracers depending on the additional
nuclides to be determined.
Note. The tracers are added here if the final solution is treated after the options FE-1
or FE-2, but not after FE-3 (see below).
3. Add enough 65% H N 0 3 to wet the ash while washing the walls with the
acid in order to collect the ash in the bottom of the flask.
4. Place the flask on a hot plate and evaporate the suspension to
dryness.
Note. The temperature of the hot plate is increased gradually to avoid bumping. To
increase the evaporation rate, isolate the neck of the graduate flask by rolling up a
sheet of paper. Fix with adhesive tape.
5. Introduce the flask in an oven at 400 °C for 30 min.
Note. At this temperature, the Mg(N03>2, coming from the Mg present in the sample,
decomposes liberating highly oxidizing nitrogen oxides which mineralize the
remaining carbon particles.
The flask contains now the carbon-free mineralized faeces.
3 . 5 .3 . L e a c h i n g
This operation brings the actinides in solution.
Procedure:
1. Add 20 ml 8 M H N 0 3 (50 ml volumetric flask) or 40 ml 8 M H N 0 3 (100
ml graduate flask) to the mineralized faeces. Swirl to disperse the
solid.
46
2. Add 0.20 ml 30% H202. Place on the volumetric flask a splash head
and an air condenser (50 cm in length).
3. Boil for 30-60 min under total reflux on a hot plate.
Note. The suspension has to boil briskly to facilitate the dissolution.
4. Remove the apparatus from the hot plate. Set aside 10 min for cooling.
5. Add 0.20 ml 30% H202 directly (not through the air condenser) into the
volumetric flask.
6. Boil for 10 min under reflux.
7. Set aside for cooling. Remove the splash head and the air condenser.
8. The volumetric flask contains the faeces solution and a small insoluble
residue.
Note. The dry weight of this insoluble residue is about 3% of that of the ash obtained
by dry ashing at 500 °C
9. Weigh the flask with the solution.
3.5.3.1. Preparation of the solution for the separation of Pu and other actinides
Below are presented three options for the processing of the faeces solution
and insoluble residue obtained in the preceding paragraph:
FE-1. Transfer the solution and the insoluble residue into a centrifuge tube.
Centrifuge. The clear supernatant is the feed solution for the
separation of Pu(IV) in the anion exchanger BIO-RAD 1-X2. Retain the
insoluble residue.
FE-2. Dilute the solution in the flask with 8 M HN03 up to the mark. Shake
well and set aside overnight. Take aliquots of the clear supernatant.
These are the feed solutions for the separation of Pu(IV) in the anion
exchanger BIO-RAD 1-X2. Retain the flask with the remaining solution
and the sedimented insoluble residue.
FE-3. Dilute the solution in the flask with water up to the mark. Shake well
and set aside overnight. Take aliquots (up to 20 ml each) of the clear
supernatant (3.2 M HN03). These aliquots are processed for the
47
separation of Pu and other actinides with the Eichrom resins UTEVA
and TRU.Spec. Reserve the flask with the remaining solution and the
sedimented insoluble residue. This option will not be treated further
here.
3.5.3.2. Insoluble residue
The residue left behind after the 8 M H N 0 3 leaching, which may contain
actinides bearing material, is treated as follows.
Procedure:
1 . Separate the insoluble residue from the 8 M H N 0 3 leachate by
centrifugation.
2. Wash the residue 2-3 times with a few millilitres of 8 M H N 0 3 and
discard the washings.
3. Transfer the residue into a Teflon dish with the help of water.
Note. It is possible to add tracers here (cf paragraph 3.4.1.2 step 9). The particles
adhering to the walls of the volumetric flask can be soaked off by a short wash with
0.5 M HF. This suspension is also transferred into the Teflon dish.
4 . Add a few millilitres of 23 M HF and evaporate to dryness.
5. Repeat step 4 twice.
Note. No further change in residue weight is usually observed after 3 evaporations,
since all the Si which can be volatilized by this method has been eliminated.
6. Add a weight of H 3 B 0 3 roughly equal to that of the residue. Add a few
millilitres of 8 M H N 0 3 and evaporate to dryness.
7. Add a few millilitres of 8 M H N 0 3 and evaporate to dryness.
8. Repeat step 7.
9. Transfer the residue into a 50 ml glass tall beaker with the help of 10
m l 8 M HN0 3 .
10. Cover the beaker with a watch glass and boil for a few minutes to
obtain a clear solution.
48
If this solution presents an insoluble residue, filter through a membrane filter,
wash with dilute HNO3. and finally with water. Measure the filter by alpha
spectroscopy.
The solution from step 10 may be added to the main leachate, and the pooled
solution is treated twice with 0.10 ml 30% H2O2 and boiled for 5 min after each
addition.
If a new Pu tracer was added on step 3, the solution is also treated with H2O2,
and afterwards the Pu(IV) is separated directly on the anion exchanger. In this
way. it is possible to know the fraction of the Pu retained in the insoluble residue.
3.5.4. Separat ion of Pu on B IO-RAD 1-X2
The procedure is that given above for the separation of Pu from other
elements (cf paragraph 2.3.3.3). The 8 M HN03 faeces extracts may be set aside
for at least 20 days without loss of Pu recovery.
3.5.5. Resul ts
The changes in weight of the faeces during the analysis are shown on Table
17. These samples were collected from several people.
Table 17: Results of different faeces weight fractions during the analysis.
liii Fresh faeces as received
(a) (n = 30) Weight
g
84.0 73.0
213.0 5.5
Ash 500*0
(n = 30) Weight %
g (b)
3.10 3.7 3.20 3.7 7.40 6.0 0.13 1.6
(a) Each sample corresponds to one defaecatior (b) Of fresh faeces (c) Of ash
Insoluble residue after leaching
(n = 23) Weight %
mg (c)
102.0 2.6 91.0 2.6
228.0 4.2 35.0 1.5
i.
Residue after HF evaporations
(n = 17) Weight %
mg (c)
24.0 0.56 22.0 0.51 65.0 1.10
8.0 0.31
49
A pool of faeces ashes from the 80's (Sample No: NR-209) was employed to
test the performance of the method as given above and with some modifications.
The results are displayed in Table 18 and seem to be fairly consistent. These
ashes were produced by dry ashing of faecal matter at 600°C followed by
repeated evaporations with HNO3 and H2O2 and finishing by a dry ashing at
600°C. Our leaching method by boiling with 8 M HNO3 for 30-60 min (cf
paragraph 3.5.3) leaves an insoluble residue of about 4%.
The results obtained with the spiked faeces ash distributed by the
PROCORAD Association are shown in Table 19. The agreement of our results
with the certified values is fairly good.
5 0
Tab le 18: Plutonium contents of dry ashed faeces NR-209.
Analysis Tracer Contents. mBq/g ash
number recovery (Reference date 1.1.92)
% 238Pu 239240Pu
1 2
3 4 5
6 7
8
9 10 11 12
13
14 15 16 17
13
19
20
21 22
23 24
25 26
27 28
29 30 31
32
33 34
35
36 37 3 P.
94.9 95.9
96.1 97.1 95.5 96.6
98.3
95.6 96.0 93.8 66.3
71.3
95.9 93.8 96.5 30.6
2 6 3
92.6
91.7
95.0
96.0
95.5
98.2 96.5
93.9 95.1 98.5 93.4 96.4
93.8 92.7
92.5 74.6
72.6
18.8 43.1
96.8 94.3
198 192
198 195 193 181
180
196 199 187 202 197
189 197 196 183 194
187
196 188
184
183
185 190
193 191 196 184
183 183 190
192 192
192 206
204
199 178
296
290
292
297
298
282
273
296
296
293
287
292
289
295
309
281
281
299
292
295
273
277
275
288
292
286
286
291
275
278
296
297
294
294
322
301
308
276
a a
a
a
a
a
a
a
a. e
a, e
b
b
b b
b
c
c
d
d
d
d
Summary
Mean Median S.D. C.V., % Max. Min
2 3 8 p u
191 192 6.9 3.6
206. 178.
239240pu
290. 292. 10.6 3.6
322. 273.
Keys
a, b: Only one sample. Aliquots
taken from the solution.
c: The samples were evaporated to
dryness with HN0 3 + HCI04 and then
leached with 8 M HN03.
d: Total dissolution with HF and HCI04.
The residue was dissolved in
8 M HN03.
e: The Pu separation was performed
with the couple UTEVA/TRU.Spec. 241Am and Z44Cm were also determined
(October 1999) with a yield tracer recovery ,243 r J A m ) of 94% in both cases;
Analysis
number
26
27
Contents, mBq/g
(Reference date 1.1.92) ?i: Am
507
498
244 Cm
107
109
51
Table 19: Actinide contents of faeces ash samples (PROCORAD) for the period 1998-2002.
Year
1998
1999
2000
2001
2002
Sample
A B
B C
A B
B C(c)
A B
Sample contents 2 3 8 p u
n
(b)
5 5
3
3
3
i
mBq
88.5 89.8
4.2
1.23
30.4
CV
%
4.5 3.4
7.1
9.6
1.6
found/ cert.
1.08 1.10
1.06
0.75
1.01
239.240pu
n
2
3 3
3 3
3 3
mBq
32.4
18.2 11.1
29.8 1.1
16.6 17.1
CV
%
5.5
4.8 10.
.9 11.
5.2 6.1
found/ cert.
1.03
0.90 1.04
1.05 0.76
0.96 0.99
24,Am (a) n
2 2
3 3
3 3
3
mBq
8.9 8.46
9.97 8.38
19.5 1.82
13.5
CV
%
1. 1.9
6.7 2.9
3.1 24.
1.6
found/ cert.
1.14 1.08
1.05 1.00
0.98 0.95
1.02
244Cm (a) n
2
3
3 3
mBq
74.8
10.
43.2 .52
CV
%
4.
5.3
4.7 24.
found/ cert.
1.01
1.02
1.04 0.82
(a) Separation performed with the tandem UTEVA/TRU.Spec (b) Number of aliquots taken from the solution containing the whole sample. (c) Contamined faeces (no spike). The comparison is made not with the certified value but with the median of all acepted values.
52
3.6. Determination of Pu in smear reactor samples
Corrosion and leaking of fuel elements into the primary coolant reactor water
leads to radioactive deposits on pipes. To analyze these deposits, the surface
under investigation is scrapped. The liberated particles are collected with a piece
of cotton-wool wrapped up on a wooden stick, coated with silicon free grease,
which attaches the particles. These sticks are the samples received in our
laboratory.
To perform the analysis, the organic matter components are mineralized and
the actinides brought into solution. When Pu is the only element to be
determined, it is separated from other elements on the anion exchanger BIO-
RAD 1-X2. The Eichrom resins UTEVA and TRU.Spec are used when Am and
Cm in addition to Pu have also to be determined.
3 .6 .1 . Samp le dissolut ion
The wet ashing method with HN03 and H2S04 described below is carried out
manually in a volumetric flask fitted with a splash head. It is also possible to do it
automatically, by using the same reagents, with a special outfit [44]. In general,
the presence of H2S04 in wet ashing methods of Ca-rich organic materials is
precluded for the determination of Pu because Pu(IV) is strongly adsorbed by
CaS04.
Procedure:
1. Add some 2 mm glass balls into a 50 ml volumetric flask (taper
14/23).
Note. Weigh (Tara) the volumetric flask with the glass balls if the aliquots taken
from the final solution are to be weighed.
2. Add 200 mg Na 2 S0 4 .
Note. The Na2SO« reacts with the H2S04 added later and avoids the formation of
neutral, hardly soluble sulfate residues during the mineralization.
53
3. Add Pu tracer as well as other tracers depending on the additional
nuclides to be determined. If preferred, they may be added later to
the aliquots taken from the final solution.
4. Add the sample.
Note. Cut off and discard the wooden stick not covered by the cotton wool. One
sample weighs about 100 mg. The procedure given here allows handling samples
up to about 500 mg.
5. Add 2 ml 12 M HCI. Swirl the flask to wet the sample. Wait at least 5
min. Heat moderately to melt the grease and facilitate the attack.
Note. The HCI dissolves readily the Fe oxides, which are the main components of
the metallic particles.
6. Add 10 ml 14 M HN03 and 1.0 ml 18 M H2S04. Isolate the neck of
the volumetric flask by wrapping around a paper sheet. Place a
stainless steel ring as ballast (0.4 kg) around the neck of the
volumetric flask, and the splash head (taper 14/23).
Note. Avoid an excess of H2SO4, which may interfere later in the radiochemical
separation <cf Table 9).
7. Place the apparatus on the Thermolyne CIMAREC 2 hot plate. Set
the heating on position 7 (about 1.3 W/cm2).
8. When the excess of HNO3 has distilled off, a charred residue is
obtained and the flask is full of white fumes of H2SO4. Then, add
some drops of 14 M HNO3 through the splash head.
Note. When the white fumes evolves, the flask bottom must be covered with a
liquid, black layer. A dry, black residue means a shortage of H?S04. If preferred.
30% H202 may be used instead of 14 M HN03.
9. Repeat the step 8 as many times as necessary to mineralize the
carbon.
Note. A pale greenish suspension is obtained. Heavy, black particles indicate not
attacked Fe-oxides. In such a case, take off the apparatus from the hot plate, cool
somewhat, and add 1-2 ml 6 M HCI through the splash head. The particles
dissolve readily. Resume heating to distil off the excess of HCI, and continue
heating until the white fumes of H2S04 appear again.
10. Remove the apparatus from the hot plate and add 20 ml 8 M H N 0 3
through the splash head. Fit an air condenser (about 50 cm in length)
54
to the outlet of the splash head (taper 14/23). Boil vigorously for 30
min under total reflux.
Note. Vigorous boiling is necessary to facilitate the leaching.
11.Take off the apparatus from the hot plate and set aside for cooling.
Remove the splash head and the air condenser.
12. Dilute the solution in the volumetric flask up to the mark (50 ml) with
water (if the actinides Pu, Am, and Cm have to be determined; this
solution is now 3.2 M in HN03) or with 8 M HN03 (if only Pu has to
be determined). Shake to mix.
13. Set aside overnight to let to settle, filter or centrifuge the solution.
Take aliquots (5 ml) from the clear solution.
3.6.2. Separat ion of Pu on B IO-RAD 1-X2
If Pu tracer is added in step 3) of the preceding paragraph, the Pu can be
separated directly from the aliquot by the usual procedure (cf paragraph 2.3.3.3).
All Pu is brought to Pu(IV) during the fuming with sulfuric acid.
If the Pu tracer is not added at that moment, proceed as follows:
1. Add the Pu tracer into a 25 ml tared beaker. Weigh in.
2. Add the 5 ml aliquot into the beaker, as well as 0.40 ml 1.0 M NaHS04
and 0.20 ml 18 M H2SOd.
3. Evaporate to dryness at medium heat. Set aside to cool.
Note. This operation brings all Pu to Pu(IV).
4. Add 10 ml 8 M HN03 to the residue. Cover with a watch glass and heat
near the boiling point for 2-3 min. Set aside to cool.
The separation of Pu from this solution is performed as usual (cf paragraph
2.3.3.3).
55
3.6.3. Resul ts
A clear solution was never obtained with the dissolution method employed.
The insoluble, solid phase is probably formed during the dissolution process
(Cr2(S04)2. SiC>2, etc), but it is free of actinides (<0.5%). This was demonstrated
by filtering the solutions and measuring the filters in the alpha spectrometer. A
control to test the completeness of the actinides dissolution may also be
performed by gamma spectrometry if 239Np and/or ,4 ,Ce and 144Ce are present,
because Np is also an actinide and Ce(lll) behaves similarly to Am(lll) and
Cm(lll).
The Pu recovery for the whole process was always higher than 95%. Only the
Pu isotopes were observed in the Pu fraction although all the samples analyzed
contained 244Cm, 242Cm and 24,Am in similar concentrations to that of Pu.
Some typical results are presented in Table 20.
Table 20: Determination of Pu in smear reactor samples.
Sample
A (a) B(a)
c
D
E
F
Aliquot
1 2 3
1 2
1 2(d)
1 2(d)
Aliquot taken
fraction
1.000 1.000
0.080 0.040 0.040
0.080 0.080
0.120 0.060
0.020 0.060
Tracer yield
%
100.4 98.4
98.5 100.5 92.8
96.4 100 (b>
108 (c) 101
117(c) 108 (c)
Pu content Bq/sample
2 3 8Pu
—
4.28 4 39 4.39
1.39 1.41
.55
.52
29.9 28.1
^ P u
—
1.33 1.37 1.43
0.47 0.52
0.25 0.25
14.4 13.4
Activity ratio
^ P u / ^ P u
—
3.22 3.21 3.08
2.96 2.71
2.20 2.08
2.08 2.09
(a) Simulated inactive smear (wood. 270 mg; cotton-wool, 105 mg; iron powder, 17 mg) (b) Supposed yield. No Pu tracer added. (c) There is no explanation for the high chemical yield. The results were not corrected for the yield. (d) Pu separated in a 2 ml Eichrom TRU-Spec column instead of BIO-RAD 1-X2.
56
3.7. Determinat ion of Pu in soil
Soil is a mixture of mineral and organic components, from which the Pu has
to be separated prior to the preparation of a source for alpha spectrometry. This
separation is detailed in the following paragraphs.
3 .7 .1 . Mineral izat ion of the organic matter by wet-dry ashing
The starting material is the dried and sieved (up to 3 mm) soil.
Procedure:
1. Add Pu tracer as well as other tracers depending on the additional
nuclides to be determined into a 400 ml tared glass beaker.
2. Weigh accurately (to the nearest 0.01 g) about 30 g of the soil in the
beaker.
3. Add slowly 14.4 M HNO3 while swirling the beaker to wet all the soil.
Cover the beaker with a watch glass and place on a hot plate at
moderate temperature to avoid bumping.
4. When the evolution of nitrous gases has subsided, remove the watch
glass and continue heating until a dry cake is obtained.
5. Introduce the beaker in a cold or hot oven and heat for 30 min at 400
°C.
Note. Copious reddish fumes evolve due to the decomposition of nitrates. A final
beige residue indicates a successful mineralization, whereas a black residue
indicates carbon, although Mn rich soils may give very dark residues. To eliminate
the carbon residue, repeat steps 3-5. If necessary (acid soils rich in organic matter),
add 2-3 g Mg(N03)2.6H20 with the HN03.
The organic matter free soil is now ready for Pu leaching.
57
3 . 7 . 2 . L e a c h i n g o f P u
Pu is brought into solution along with carbonates and oxides, whereas silicates
remain in the insoluble residue.
Procedure:
1 . Introduce a Teflon coated stirring bar into the beaker containing the
mineralized soil.
Note. A large bar is necessary to insure thorough dispersion of the soil during the
leaching. A wedge-shaped 55 mm long bar weighing about 18 g proved to be very
efficient.
2. Add slowly 100 ml 8 M HN0 3 . Cover the beaker with a large watch
glass. Stir to break the cake and disperse the soil. Add then 2 ml 30%
H 2 0 2 .
Note. The H202 reduces the Mn oxides formed from the decomposition of Mn(N03)z
in the oven (step 5 in the preceding paragraph) to Mn(ll). It reduces also practically
any oxidizing agent. Moreover, it realizes the Pu isotopic equilibrium between sample
and tracer (cf paragraph 2.3.5).
3. Boil while stirring for 1 h.
Note. Adjust the stirring speed to insure thorough mixing. Do no heat more than
necessary to keep the solution boiling. Adding water in the watch glass is also useful
to avoid excessive solvent losses.
4 . Set aside the beaker for cooling for about 5 min. Add 2 ml 30% H2O2.
Place immediately the beaker on the hot plate. Resume boiling and
stirring for 5 min.
Note. The H202 ensures the Pu isotopic equilibrium between sample and tracer (cf
paragraph 2.3.5). It decomposes readily in hot 8 M HN03.
5. Let the solution cool down to room temperature.
6. Filter through a 5.5 cm diameter Whatman GF/A or B filter placed on
the plate of a porcelain Buchner funnel, which is fitted into a filter flask.
Apply a slight vacuum to stick the filter to the plate and to speed the
filtration while avoiding cracking the soil.
7. Wash the beaker with 5-10 ml 8 M H N 0 3 and add the washing into the
funnel. Collect the filtrate with the main solution in the filter flask.
58
8. Repeat step 7. Then apply the vacuum for several minutes to recover
the solution retained by the leached soil.
Note. The pooled filtrate has to be clear. Filter again if necessary.
9. This solution (100-120 ml, 8 M HN03) is the feed solution for the
separation of Pu(IV) with the anion exchanger BIO-RAD 1-X2.
Note. This solution remains clear and without deposit at least over three months. On
the contrary, soil extracts in 6 M HCI precipitates silicic acid almost continuously.
3.7.3. Separation of Pu on BIO-RAD 1-X2
The separation of Pu(IV) from this solution is performed in the usual manner (cf paragraph 2.3.3.3)
3.7.4. Resul ts
The reproducibility and the accuracy of the Pu determinations are good, as
shown in Tables 21 and 22, respectively. Thus, the given analytical procedure
appears to work properly.
We stated above (cf paragraph 2.3.1) that Pu in soils contaminated by global
fallout can be brought in solution by leaching with boiling 8 M HNO3. This
leaching was also effective to dissolve the Pu bearing materials from IAEA-385
Irish Sea Sediment (cf Table 22), which were certainly not originated by the
global fallout. No Pu (less than 2%) was left behind in the insoluble residue, as
was shown by dissolving the residue in HF.
The Pu tracer recovery for a series of soil analysis (34 samples) ranged from
30 to 80%, with a mean of 61%. No data was available at that time about the
oxidation state of Pu in the tracer solutions employed.
The Pu recovery is not affected by the waiting time (1-11 days) between
leaching and separation, the flow rate ( 1 - 5 ml/min) of the feed solution through
the anion exchanger, and the bed length of the standard column. Thus, when soil
leachates prepared as stated above (cf paragraphs 3.7.1 and 3.7.2) were passed
59
through a tandem composed of two identical standard columns, about 80% of the
Pu was fixed in the top column but less than 0 . 1 % in the bottom column.
Table 21: Determination of 239240Pu in soils and sediments- Reproducibility.
Matrix Sample Aliquot 239.24opu E r f Q f ( 3 )
number Bq/kg
Soil A 0.623 3.0 2.4
2.1 3.0
3.0 1.6 1.6 1.7
2.1 2.6
4.6 2.6
3.1 2.3
6.0 4.0 4.5 9.6
4.3 2.6 2.3 3.2 3.7
Marine sediment A 3.24 2.3 2.7 2.2
(a) This is the statistical error (1 s) associated to the radioactivity measurements
1 2
1 2
1 2 3 4
1 2
1 2
1 2
1 2 3 4
1 2 6 9 10
1 2 3
0.623 0.626
0.568 0.573
0.765 0.750 0.762 0.754
0.746 0.739
0.571 0.578
0.828 0.741
0.184 0.176 0.177 0.177
0.561 0.549 0.565 0.557 0.540
3.24 3.21 3.17
Series Values Degrees CV, % of freedom
9 26 17 2.07
60
Table 22: Determination of239 2d0Pu in soils and sediments - Accuracy.
Soil
Soil Kiel 1995 (b)
IAEA Soil-6 (d)
IAEA-385 Irish Sea Sediment (e)
Sample
A B
A B
A B C
weight
9
30.3 29.8
14.18 10.21
10.294 8.258 9.984
Ashing
method
_ (a) .
w + d w + d
d ( 1 6 h , 500°C) d ( 1 6 h , 500°C)
w + d d ( 1 0 h , 500°C) d ( 1 0 h , 500°C)
Tracer yield 2 '2Pu
%
70.2 74.9
81.4 85.6
64.9 57.5 67.8
Soil content, Bq/kg 23W40Ru
Value
1.13 1.16
1.038 1.045
3.24 3.21 3.17
error (1s)
0.05 0.05
0.021 0.023
0.075 0.087 0.070
^ P u Value
19.8(c) 18.5 (c)
0.504 (f) 0.487 (f) 0.482 (f)
error (1s)
0.6 0.5
0.021 0.025 0.020
(a) The standard procedure (wet + dry ashing) or dry ashing alone. (b) Report. Bundesanstalt fur Milchforschung, Institut fur Chemie und Physik, "Ergebnisse der Ringanalyse Boden 1995/96",
Kiel, Marz 1996. Results (p. 3) 236Pu: 19.4 +- 0.6 Bq/kg; ^ ^ P u : 1.1 +- 0.1 Bq/kg
(c) Reference date 1.1.1996 (d) Reference sheet Reference Material IAEA Soil-6 and Report IAEA/RL/111
Recommended value 239240Pu: 1.04 Bq/kg, 95% conf. Interval 0.96-1.11 (e) P.P. Povinec & M.K. Pham, Report on the Intercomparison Run IAEA-385 Radionuclides in Irish Sea Sediment
International Atomic Energy Agency, Monaco. 2003 238Pu.Median of acepted laboratories (n=35 of 39): 0.48 Bq/kg, confidence interval (95%) 0.48-0.50 23924QI-N.- t i - j : Pu. Median of acepted laboratories (n=43 of 50), 2.9 Bqk/g, confidence interval (95%) 2.81-3.14
(0 Reference date 1.1.1996
61
All the Pu(IV) added to soil (35 g) leachates or to earth crust synthetic
solutions (10 g earth crust) was quantitatively recovered (>97%) (cf Table 9, Exp.
15-19).
Therefore, the Pu recovery of the overall separation is the fraction of Pu that
enters the column as Pu(IV). The only way to increase the yield is to bring all Pu
oxidation states to Pu(IV).
In order to study a possible influence on the isotopic exchange of Pu, the
following parameters were tested: (i) the ashing method (wet plus dry ashing or
dry ashing alone), (ii) the step at which the tracer is added in the analytical
procedure (before or after ashing), and (iii) the addition - or not - of H2O2,. The
results of these experiments are shown in Table 23.
Practically identical 239Pu soil contents were found for the series A, B and C,
whereas D shows a lower content. On the other hand, series D has the higher
tracer yield, which is nearly quantitative. This suggests that in series D the added
tracer 242Pu(IV) remains in this oxidation state and does not undergo a complete
isotopic exchange with the 239Pu of the sample.
Comparison of series A and B indicates that the isotopic exchange is realised
during the wet and dry ashing step and the 239Pu content in soil is unaffected by
the H2O2 treatment, and in addition its presence increases the formation of
Pu(IV).
After a dry ashing, the treatment with H2O2 is mandatory, as may be seen
when comparing series C and D. This treatment allows the isotopic exchange in
the series C. It is therefore recommended to perform the H202 treatment in all
cases.
62
Tab le 23: Pu isotopic exchange between soil sample and tracer.
Soil Experiment aliq. Ashing Tracer added H 20 2 Tracer yield, %
series number added during value mean (a) (b) (c) (d) leaching
S.D.
Pu soil content, Bq/kg
Value absolute
0.561 0.555 0.565
0.549 0.569 0.579 0.540
0.557 0.540
0.503 0.481
error (1s)
0.024 0.014 0.013
0.015 0.015 0.018 0.016
0.018 0.020
0.014 0.014
mean
0.560
0.559
0.549
0.492
S.D-
0.005
0.018
0.012
0.016
B
D
1 2 3
1 2 3 4
1 2
1 2
w + d w + d w + d
w + d w + d w + d w + d
d d
d d
before ashing before ashing before ashing
before ashing before ashing before ashing before ashing
after ashing after ashing
after ashing after ashing
yes yes yes
no no no no
yes yes
no no
71.3 71.8 78.8
62.2 56.7 59.9 69 2
63.1 60.7
96.8 97.1
74.0
62.0
619
97.0
4.2
5.3
1 8
0.2
(a) In the soil aliquotes of series A, ashing as well as tracer and H202 additions were performed as in the standard procedure (cf paragraphs 3.7.1. and 3.7.2.). In series B - D, only the parameters given here were changed with respect to the standard procedure. (b) Soil NR-324, 30 g aliquotes. Top forest soil, Ca-rich. LOI <500°C): 35%. (c) w + d: wet ashing followed by dry ashing (the standard procedure); d: dry ashing (500°C, 24 h).
(d) A solution of 242Pu(IV)-sulfate in 0.10 M NaHSO,.
63
4. References
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Radiochimica Acta. 61(1993)115-122.
2) Weigel, F., Katz, J.J., Seaborg, G.T., Plutonium. In The Chemistry of the
actinide elements. Second edition. Vol. 1. Edited by, J.J. Katz, G.T.
Seaborg, and L.R. Morss. Chapman and Hall, London, 1986, p. 501.
A new edition of this comprehensive treatise has been recently published:
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Editor), The chemistry of the actinide and transactinide elements. Springer,
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Effects of Ionizing Radiation. UNSCEAR 2000 Report to the General
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4) Krey, P.W., Atmospheric burn-up of a plutonium-238 generator, Science
158(1967)769-771.
5) Bajo, S., Calibration of an alpha-spectrometer with electrodeposited
uranium sources. Internal report TM-23-96-14, Paul Scherrer Institute, CH-
5232 Villigen PSI, October 1996. (This report contains some pictures of the
electrodeposition unit).
6) Bajo, S. and Eikenberg. J., Electrodeposition of actinides for alpha-
spectrometry, J. Radioanal. Nucl. Chem. 242(1999)745-751.
7) Taylor, S. R., Abundance of chemical elements in the continental crust: a
new table, Geochim. et Cosmochim. Acta, 28(1964)1273-1285.
Useful information about this topic also in:
Paul, E. A. and Huang, P. M., Chemical Aspects of Soil, in The Handbook of
Environmental Chemistry, Vol. 1, Part A. Edited by O. Hutzinger. Springer,
Berlin,1980.
64
Puchelt. H., Environmental Inorganic Geochemistry of the Continental Crust,
in The Handbook of Environmental Chemistry, Vol. 1, Part F. Edited by O.
Hutzinger. Springer, Berlin, 1992.
8) Bajo. S. and Eikenberg, J., Preparation of a stable solution of Pu(IV),
Radiochim. Acta 91(2003)495-497.
9) Kressin, I.K., Moss, W.D., Campbell, E.E., Plutonium-242 vs Plutonium-236
as an analytical tracer, Health Physics 28(1975)41-47.
10) Harvey, B.R., Lovett, M.B., The use of yield tracers for the determination of
alpha-emitting actinides in the marine environment, Nucl. Instr. Meth. in
Phys. Res. 223(1984)224-234.
11) Harvey, B.R., Lovett, M.B., Yield tracer applications in the determination of
man-made radionuclides at low environmental concentrations, in Low-level
measurements of man-made radionuclides at low environmental
concentrations. Edited by M. Garcia-Leon and G. Madurga. World Scientific,
Singapore, 1991, pp. 217-238.
12) Chemical yield tracers for radiochemical analysis, in Environmental
Radiochemical analysis. Edited of behalf of the Radiochemical Methods
Group of the Royal Society of Chemistry: Edited by G.W.A. Newton. Special
Publication No. 234, Cambridge, 1999, p. 272-282.
13) Chen, Q., Dahlgaard, H., Nielsen, S.P., Aarkrog, A., 242Pu as tracer for
simultaneous determination of 237Np and 239240pu in environmental
samples, J. Radioanal. Nucl. Chem., 253(2002)451-458.
14) Bajo, S., Dissolution of matrices. In Preconcentration Techniques for Trace
Elements, Alfassi, Z. B., and Wai, C. W., Editors, CRC Press, Boca Raton,
1992. pp. 3-31.
15) Sulcek, Z. and Povondra. P.. Methods of Decomposition in Inorganic
Analysis, CRC Press, Boca Raton, 1989.
16) Heinrichs, H. and Herrmann, A. G., Praktikum der Analytischen Geochemie,
Springer, Berlin, 1990.
65
17) Stoeppler, M., Editor, Probennahme und Aufschluss, Springer Labormanual,
Springer, Berlin, 1994.
18) Stoeppler. M.. Editor, Sampling and Sample Preparation (Practical Guide for
Analytical Chemists), Springer, Berlin, 1997.
19) Kingston, H. M. and Haswell, S. J., Editors, Microwave-Enhanced
Chemistry, American Chemical Society, Washington D.C., 1997.
20) Krey, P.W., Bogen, D.C, Determination of acid leachable and total
plutonium in large soil samples, J. Radioanal. Nucl. Chem., Articles
115(1987)335-355.
21) Tamura, T., Distribution and characterization of plutonium in soils from
Nevada Test Site, J. Environ. Qual. 4(1975)350-354.
22) Sill, C.W., Some problems in measuring plutonium in the environment.
Health Physics 29(1975)619-626.
23) Sill, C. W., Sill, D. S., Sample Dissolution, Radioactivity & Radiochemistry
6(1995)8-14.
24) Sill. C. W., Problems of sample treatment in trace analysis, in Proc. 7th IMR
Symp. Accuracy in Trace Analysis: Sampling, Sample Handling, and
Analysis, Spec. Publ. 422, National Bureau of Standards, Gaithersburg, MD,
1976. (This paper contains some photographs of potassium fluoride and
pyrosulfate fusions of a soil)
25) McDowell. W.J., Farrar, D.T., Billings, M.R., Plutonium and uranium
determination in environmental samples: combined solvent extraction-liquid
scintillation method, Talanta 21(1974)1231-1245.
26) Croudace, I.W., Warwick, Ph.E., Taylor, R.N., Cundy, A.B., Investigation of
an allegated nuclear incident at Greenham Common Airbase using Tl-mass
spectrometry measurements of uranium isotopes, Environm. Sci. Technol.
34(2000)4496-4503.
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27) Erdmann. N., Hermann, G, Huber, G., Kohler, S., Kratz, J.V., Mansel, A..
Nunnemann. M., Passler. G., Trautmann, N., Turchin, A., Waldek, A.,
Resonance ionization mass spectrometry for trace determination of
plutonium in environmental samples, Fresenius J. Anal. Chem.
359(1997)378-381.
28) Burnett, W.C.. Corbett. D.R.. Schultz, M.. Horwitz. E.P., Chiarizia, R., Dietz,
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29) Schuttelkopf, H., Entwicklung einer Analysenmethode fur Plutonium im
Femtogramm/Gramm-Bereich und ihre Anwendung auf Umweltproben,
Kernforschungszentrum Karlsruhe, Report KfK 3035, Karlsruhe, September
1981. p. 48.
30) Biorad Laboratories, Guide to Ion Exchange, Catalog Number 140-9997. 56
pages, Richmond, no date.
31) Korkisch, J., Handbook of Ion Exchange Resins: Their Application to
Inorganic Analytical Chemistry, Five volumes. (Volume II deals with the
actinides). CRC Press, Boca Raton, 1989.
32) Dietz, M.L, Horwitz, E.Ph., Novel chromatographic materials based on
nuclear waste processing chemistry, LC-GC The Magazine of Separation
Science 11(1993)No.6, 7 pages.
33) Kressin. I.K., Waterbury, G.R., The quantitative separation of Pu from
various ions by anion exchange, Anal. Chem. 34(1962)1598-1601.
34) Reference 31. Vol. II. pp. 22-25.
35) IAEA, Measurement of radionuclides in food and the environment (A
guidebook). Technical Report Series No. 295, International Atomic Energy
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and biological samples by ion exchange, Anal. Chem. 43(1971)1827-1830.
67
37) Chen, Q.. Aarkrog, A.. Nielsen, S.P., Dahlgaard, H., Nies, H., Yu, Y.,
Mandrup, K., Determination of plutonium in environmental samples by
controlled valence and anion exchange, J. Radioanal. Nucl. Chem.
172(1993)281.
38) Campbell, E.E., Moss, W.D., Determination of Pu in urine by anion
exchange. Health Physics 11(1965)737-742.
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40) Jeffery. G.H., Bassett, J., Mendham, J., Denney, R.C., Vogel's textbook of
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of silicates by atomic absorption spectrometry, Anal. Chem. 40(1968)1682.
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68
5. Appendix
5.1. Nuclear characteristics of some Pu isotopes
Data from IAEA Decay data of the transactinium nuclides, Technical Report
Series No. 261. International Atomic Energy Agency. Vienna, 1986, and W.
Westmeier and A. Merklin Catalog of alpha particles from radioactive decay,
Fachinformationszentrum Energie, Physik und Mathematik GmbH. Report No.
29-1. Karlsruhe, 1985.
Table A: Nuclear characteristics of the Pu isotopes from mass 238 to 242.
Isotope
23BPu 239Pu 2d0Pu 2 4 1 R u
2«pu
Isotopic mass
238 239 240 241 242
Half-life
years
8.770E+01 2.411E+04 6.563E+03 1.440E+01 3.735E+05
Specific activity
Bq/g
6.337E+11 2.296E+09 8.398E+09 3.812E+12 1.463E+08
Bq/atom
2.505E-10 9.110E-13 3.347E-12 1.525E-09 5.881E-14
69
Table B: Alpha decay data of 235Pu,"3Pu,
Isotope Half-life
Years
"6Pu 2.851
238Pu 87.700
239Pu(b) 24110.000
240Pu 656.300
242Pu(b) 373500.000
Pu. Z40Pu and 2i2Pu (a).
Alpha energy Emission probability
(alpha/decay)
keV %
5614.10 5721.00 5767.70 5357.70 5456.50 5499.21 5105.50 5143.80 5156.70 5021.50 5123.68 5168.17 4856.20 4900.50
0.180 31.700 68.100
0.102 28.840 71.040 11.800 15.000 73.100
0.089 27.000 72.900 23.480 76.490
(a) In bold type Ihose isotopes normally used as tracers (b) Without those energies with an emission probability lower than 0.1%.
70
Table C: Alpha decay data of 236Pu, 236Pu, 239Pu, 240Pu and 242Pu (a), ordered by
increasing energy.
Isotope Alpha energy Emission probability (alpha/decay)
(a)
w p u 242 Pu 2 4 0Pu 2 3 9Pu 2 -0p u
2 3 9Pu 2 3 9Pu 2 4 0Pu 2 3 8Pu 2 3 6Pu 2 3 8Pu 2 3 6Pu 2 3 6Pu 236pu
keV
4856.20 4900.50 5021.50 5105.50 5123.68 5143.80 5156.70 5168.17 5357.70 5456.50 5499.21 5614.10 5721.00 5767.70
%
23.480 76.490 0.089
11.800 27.000 15.000 73.100 72.900 0.102
28.840 71.040 0.180
31.700 68.100
(a) In bold type those Isotopes normally used as tracers.
71
Table D: Decay data of Pu and its progeny
Isotope
(decay
chain) 236Pu 2 3 2 u 228Th 224Ra 220Rn 2 . 6 p 0
2,2Pb 2,2Bi
2,2Po
**n 208pb
Half-life
2.851 a 68.90 a 1.913 a 3.665 d 55.6 s 0.150 s 10.64 h
60.55 m
298 ns 3.05 m
stable
Decay
alpha alpha alpha alpha alpha alpha alpha alpha
(a). beta (b) alpha beta
Isotope
(by increasing
energy) 2»U
228Th 228Th 2 3 2 u 2 3 2 u " T h ^ h 224Ra
236Pu 224Ra 216Pu 236Pu 2,2Bi 2,2Bi 2,2Bi
220Rn 2,6Po 2,2Po
Alpha energy
keV
5139.0 5172.6 5207.3 5263.41 5320.17 5340.54 5423.33 5444.60
5614.1 5685.6 5721.0 5767.7 5768.10 6051.0 6090.1 6288.3 6778.5 8784.4
Emission probability
(alpha/decay) %
0.30 0.210 0.395
31.7 68.0 26.70 72.7
5.0
0.18 94.98 31.7 68.1
1.67 70.2 26.8 99.9
100 100
(a) 35.94%. (b) 64.06%.
72
Table E: Alpha decay data of 236Pu and its progeny, 238Pu, 239 Pu, and 240Pu ordered by
increasing energy (a).
Isotope
w , 23* ,
240, 232i 239,
239Pu 2 4 0 R u
22BTh 223Th 232(J
232U 22aTh
JPu >Th 'Ra
E (keV)
Emission probability (alpha/decay) (%)
'Pu 'Pu 'Pu 'U 'Pu
238 r
228-
224f
238Pu 238Pu 2 3 6 p u
224Ra 2 3 6 p u
2 3 6 p u 2 '2e/ 2 '2e/ 2 '2e/ 220Rn 2,6Po 2,2Po
5021.5 5105.5 5123.68 5739.0 5143.8 5156.70 5168.17 5772.6 5207.3 5263.41 5320.17 5340.54 5357.7 5423.33 5444.60 5456.5 5499.21 5614.1 5685.6 5721.0 5767.7 5768.10 6051.0 6090.1 6288.3 6778.5 8784.4
0.089 11.8 27.0
0.30 15.0 73.1 72.9
0.210 0.395
31.7 68.0 26.70
0.102 72.7 5.0
28.84 71.04
0.18 94.98 31.7 68.1
1.67 70.2 26.8 99.9
100 100
(a) Pu progeny in italic type.
P A U L S C H E R R E R I N S T I T U T
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