y. danon gaerttner linac center rensselaer polytechnic ... · wpec meeting, sg-35, may 22, 2013 ....
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1 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Measurement of Neutron Scattering as Benchmark for Nuclear Data Evaluations
Y. Danon Gaerttner LINAC Center
Rensselaer Polytechnic Institute, Troy, NY, 12180
WPEC Meeting, SG-35, May 22, 2013
2 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Collaboration • RPI
– Faculty:
• Dr. Y. Danon, Dr. E. Liu
– Staff • P. Brand - Technical Manager
• M. Gray, M. Strock, A. Kerdoun - Linear Accelerator Technicians
– Graduate Students (in the Nuclear Data group):
• A. Daskalakis, R. Bahran, D. Williams, J. Thompson, Z. Blain, B. McDermott,, S. Piela
• KAPL – Dr. T. Donovan, Dr. G. Leinweber, Dr. D. Barry, Dr. M. Rapp, Dr. R. Block,
B. Epping
3 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Objectives
• Provide accurate benchmark data for scattering cross sections and angular distributions in the energy range from 0.5 to 20 MeV
• Can be developed to provide differential elastic and inelastic scattering cross section measurements
• Design a flexible system: now also used for fission neutron spectra measurements
4 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Methodology
• Measure the scattering yield at several angles around the sample. – Use TOF to measure the neutron incident energy
– Use detectors that are insensitive to (capture/inelastic/background) gamma
• Compare the measurements to detailed simulations of the system with different cross section libraries – Characterize the incident neutron flux
– Characterize the neutron detection efficiency
• Identify energy/angle regions where improvement is needed.
5 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
TOF Scattering Yield Measurement
L1,t1,E1
L2,t2,E2
• Measure the total TOF t=t1+t2
• For all scattering events E2<E1
• In most cases the energy loss is small E1~E2
• Since t1>>t2 and E1~E2 then for presentation the incident neutron energy E1 is calculated using t and L=L1+L2
1
1
1)(
2
2
tc
LcmtE nL2~0.5m
L1~30m
6 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
First Order Approximation of the Scattering Yield
2
),(1)()'(),(
)( EfeEEEY
LET
Detector Efficiency
Incident Flux
Probability to Interact
Probability to Scatter in direction
In this approximation - multiple scattering is ignored
7 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Experimental Setup Overview
8 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Scattering Detection System: Experimental Setup
Pioneered the use of
Red Bull can for
nuclear physics
(as low mass sample
holder)
9 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Scattering Detection System: Experimental Setup
• Detector Array – 8 EJ301 Liquid Scintillation Detectors – 8 A/D channels – Pulse Shape discrimination in TOF
• Data Processing System – Data Processing Computer (SAL) –
Control Room
• Computer Controlled Power Supply – Chassis - SY 3527 Board - A1733N
• Sample Holder / Changer
Neutron Beam
Detector Array
Acqiris AP240 DAQ Board
PCI Chassis Extention
CAEN Computer
Controlled Power Supply
Printer
HAL
Dell -
Precision
670
SAL
Data Analysis Computer
(Control Room)Data Collection
Computer
(25m Station Room)
10 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
DAQ system • All DAQ is automated using script based software running under Windows
• Alternate between sample, graphite and open (background) measurements
• Each position is measured for about 10 min
• Fission chamber monitors are used to normalize beam intensity fluctuations.
• Detector/system gain is periodically aligned using 22Na
11 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Neutron Gamma Separation with Pulse Shape Analysis
• Digitize 120 ns to get all the event-generated detector pulses
• Use pulse shape analysis to discriminate gammas
• Works effectively for E>0.4 MeV
12 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Flux Shape Measurement
• Use a fission chamber with ~391 mg 235U in the sample position
• Use ENDF/B 7.1 fission cross section for 235U
• Correct for transmission of all materials between the source and sample
• Compare to a similar measurement using EJ301 and SCINFUL calculated efficiency
• Combine the two data sets using fission for E< 1 MeV
0.4 1 10 3010
-3
10-2
10-1
100
101
2x101
Targ
et F
lux S
hape [
#/e
V/c
m2]
Energy [eV]
Fission Chamber
EJ-301
MCNP
13 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Efficiency as a Function of Energy • Objective:
– MCNP simulation of EJ301 response in the sample position must precisely agree with the measurement
• Methodology: – Use the measured flux as a source
in MCNP simulation of the in-beam detector response
– In MCNP set the detector efficiency =1 (tally only the neutron flux shape)
– Divide the measured response by the simulation results to get the efficiency (E) for each detector
– During the experiment periodic gain calibrations are done to minimize gain shift.
0.4 1 10 200.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d E
ffic
iency
Energy [MeV]
Detector 1
Detector 2
Detector 3
Detector 4
Detector 5
Detector 6
Detector 7
Detector 8
500 1000 1500 2000 2500 3000
0
500
1000
1500
2000
2500
0.51251020
Energy [MeV]
Counts
[5 n
s b
ins]
Time [ns]
In-beam Data
MCNP Calculation
14 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Neutron Beam Collimation • Characterize the collimation system
– Ensure beam diameter agrees with sample diameter of 7.62 cm
– Verify measurements and calculations agree
15 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
• Sum all files and dead-time correct.
• The experimental count rate corrected for
background, Ri, was obtained by subtracting
monitor normalized open data, RiO, by sample
data, RiS, for each channel, i:
Data Reduction
O
iO
SS
ii RM
MRR
16 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
MCNP Simulation Geometry • Use ASAP (As Simple As Possible) approach • Use array of point detector tally F5 to model the EJ301 detector
– Convolute the tally with the detector efficiency
• Include ¾” Depleted U filter in the simulation • Include windows (Al) • Include recent improvements of vacuum tube near the sample
17 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Data Analysis • Compare the shape (as a function of TOF) between the measurements and
simulations • Use graphite as a reference in all measurements
– Differences between the measurement and simulation of graphite are considers systematic errors
• Measurements of Be, Mo and Zr – The efficiency was derived from SINCFUL calculations – Neutron flux shape based on a fit to in-beam measurements with EJ-301 and
Li-Glass – Used individual detector normalization of the simulation to the experimental
data based on graphite measurement
• For 238U and 56Fe experiment – Flux was derived from 235U and EJ301 in-beam measurements – The efficiency was adjusted to match the MCNP calculations to the in-beam
measured data – Use one normalization factor for all detectors (global normalization)
18 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
0 500 1000 1500 2000 2500 3000 3500 40000
200
400
600
800
1000
1200
140012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
EJ301 Detector scattered flux at 140deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
200
400
600
800
1000
1200
140012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
EJ301 Detector scattered flux at 90deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
200
400
600
800
1000
1200
140012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
EJ301 Detector scattered flux at 52deg
Experimental Data
Simulation with ENDF7
Carbon Experimental Results for Be measurement
0 500 1000 1500 2000 2500 3000 3500 40000
200
400
600
800
1000
1200
140012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
EJ301 Detector scattered flux at 26deg
Experimental Data
Simulation with ENDF7
0.5 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
0.5
1.0
1.5
2.0
2.5
3.0
Cro
ss S
ectio
n (
b)
Energy (MeV)
7 cm
13 cm
ENDF/B-7.0
Cro
ss S
ectio
n (
b)
Energy (MeV)
7 cm
13 cm
ENDF/B-7.0
Total cross section
19 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Beryllium Experimental Results 4cm
8cm
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
140deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
90deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
52deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
26deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
140deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
90deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
52deg
Experimental Data
Simulation with ENDF7
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
26deg
Experimental Data
Simulation with ENDF7
20 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Molybdenum Experimental Results 5cm
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
6000
700012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
140deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
6000
700012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
90deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
6000
700012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
52deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
6000
700012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
26deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
8cm
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
140deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
90deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
52deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
0 500 1000 1500 2000 2500 3000 3500 40000
1000
2000
3000
4000
5000
600012510100 0.10.20.30.5
Time of Flight (nsec)
Counts
/Channel
Energy (MeV) at 30.1m
26deg
Experimental Data
ENDF6.8
JEFF3.1
ENDF7.0
21 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Zr – 6 cm Thick Sample
26 deg
72 deg 90 deg
52 deg
22 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Zr – 10 cm Thick Sample
26 deg
72 deg
52 deg
90 deg
23 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
72deg
90deg 140 deg
Carbon Standard For Zr Experiment
26 deg
24 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Comparing Experiments and Evaluations
• The MCNP calculations and experimental data were
used to calculate C/E values in several different
scattering angles and energy regions between 0.5 MeV
and 20 MeV.
• Differences between MCNP simulations of the carbon
standard and the experiment were treated as
systematic errors
25 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
C/E for 6 cm Zr sample 26 deg
72 deg 90 deg
52 deg
26 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
C/E for 10 cm Zr sample 26 deg
72 deg 90 deg
52 deg
27 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Observations for Zr
• Overall there is good agreement between the experiments and calculations.
• For the energy group of 10 MeV to 20 MeV the C/E values for all libraries were significantly greater than unity, indicating that the experimentally observed differential scattering cross section is less than the one used in the evaluated library.
28 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
238U Scattering - Forward Angles
500 1000 1500 2000 2500 30000
2000
4000
6000
8000
100000.10.51251020
Energy [MeV]
Counts
Time of Flight [ns]
Graphite Data
MCNP Results
29 deg
Library c2
ENDF/B-VII.1 2.6
ENDF/B-VI.8 1.9
JENDL-4.0 1.7
JEFF-3.1 2.0
500 1000 1500 2000 2500 30000
2000
4000
6000
8000
100000.10.51251020
Energy [MeV]
Counts
Time of Flight [ns]
Graphite Data
MCNP Results
60 deg
Library c2
ENDF/B-VII.1 1.6
ENDF/B-VI.8 3.7
JENDL-4.0 1.2
JEFF-3.1 2.1
500 1000 1500 2000 2500 30000
2000
4000
6000
8000
10000
12000
14000
160000.10.51251020
29 deg
Energy [MeV]
Counts
Time of Flight [ns]
Uranium Data
ENDF/B-VII.1
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
500 1000 1500 2000 2500 30000
1000
2000
3000
4000
5000
6000
7000
80000.10.51251020
60 deg
Energy [MeV]
Counts
Time of Flight [ns]
Uranium Data
ENDF/B-VII.1
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
29 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
238U Scattering – Back Angles
500 1000 1500 2000 2500 30000
2000
4000
6000
8000
100000.10.51251020
Energy [MeV]
Counts
Time of Flight [ns]
Graphite Data
MCNP Results
113 deg
Library c2
ENDF/B-VII.1 0.4
ENDF/B-VI.8 2.7
JENDL-4.0 0.5
JEFF-3.1 0.9
500 1000 1500 2000 2500 30000
2000
4000
6000
8000
10000
120000.10.51251020
Energy [MeV]
Counts
Time of Flight [ns]
Graphite Data
MCNP Results
153 deg
Library c2
ENDF/B-VII.1 3.7
ENDF/B-VI.8 4.9
JENDL-4.0 1.2
JEFF-3.1 4.7
500 1000 1500 2000 2500 30000
500
1000
1500
2000
2500
3000
3500
40000.10.51251020
113 deg
Energy [MeV]
Counts
Time of Flight [ns]
Uranium Data
ENDF/B-VII.1
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
500 1000 1500 2000 2500 30000
1000
2000
3000
4000
50000.10.51251020
153 deg
Energy [MeV]
Counts
Time of Flight [ns]
Uranium Data
ENDF/B-VII.1
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
30 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Observations for 238U
• Differences between the evaluations are visible and exceed the experimental errors.
• To get better agreement the evaluation need to be adjusted mostly at back angles.
• Overall JENDL 4.0 has has the lowest c2
31 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
2500 2550 2600 2650 2700 2750 28000
200
400
600
800
1000
1200
1400
1600
1800
2000
22000.10.51251020
153 deg
Energy [MeV]
Counts
Time of Flight [ns]
Fe56 Data
ENDF/B-VII.0
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
56Fe Scattering Measurement – Results 153°
The energy resolution is
sufficient to show some
discrepancies in the resonance
region (E<850 keV)
500 1000 1500 2000 2500 30000
200
400
600
800
1000
1200
1400
1600
1800
2000
22000.10.51251020
153 deg
Energy [MeV]
Counts
Time of Flight [ns]
Fe56 Data
ENDF/B-VII.0
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
32 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
1800 1900 2000 2100 2200 23000
200
400
600
800
1000
1200
1400
1600
1800
2000
22000.10.51251020
153 deg
Energy [MeV]
Counts
Time of Flight [ns]
Fe56 Data
ENDF/B-VII.0
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
Fe-56 Scattering Measurement – Results 153° • Above the first inelastic state
(E>847 keV) there are some
differences with the evaluations
• We are exploring the possibility to
extract double differential cross
section data from these experiments.
500 1000 1500 2000 2500 30000
200
400
600
800
1000
1200
1400
1600
1800
2000
22000.10.51251020
153 deg
Energy [MeV]
Counts
Time of Flight [ns]
Fe56 Data
ENDF/B-VII.0
ENDF/B-VI.8
JENDL-4.0
JEFF-3.1
33 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
O-16 in a Water Sample • A Scoping calculation
showing H2O scattering calculate using ENDF/B-7.1 and JENDL 4.0
• Differences are visible at back angle between 2-3 MeV
• Easy normalization of the experiment and simulations at the 1 MeV resonance
• D2O might be a better sample because of lower contribution from the D 500 1000 1500 2000 2500 3000
0
500
1000
1500
2000
2500
3000
3500
Co
unts
TOF [ns]
H2O at angle=150 deg
ENDF/B-7.1
JENDL-4.0
1 MeV
2.34 MeV
34 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Future Development • Use an array of BaF2 detectors to provide a gamma tag
– Enables separation of inelastic scattering from elastic scattering.
• Use Filtered beams to measure inelastic scattering
• Use thin samples to obtain double differential scattering cross section.
＊
E1
L1~30 m
E2 L2=0.5-1 m
Gamma Detectors
(top view)
Neutron Detectors
Sample
35 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Conclusions
• The system developed at RPI measures the neutron scattering yield and fission neutron emission from a sample
• Simulation of the system with different libraries shows differences from the experimental data
• The accuracy of the experiments provides: – A recommendation of which evaluated library is
best for treatment of neutron scattering
– Pinpoint the differences in angle and energy and provide information to evaluators.
36 Mechanical, Aerospace and Nuclear Engineering nacThe Gaerttner LINAC Center
Related Publications • Devin P. Barry et al., “Quasi-differential Neutron Scattering in Zirconium from 0.5 MeV to 20 MeV”,
Nuclear Science and Engineering, Accepted For Publication (2012).
• Adam M. Daskalakis, Rian M. Bahran, Ezekial J. Blain, Brian J. McDermott, Sean Piela, Yaron Danon, Devin P. Barry, Greg Leinweber, Robert C. Block, Michael J. Rapp, “Quasi-Differential Neutron Scattering Measurements of 238U”, ANS Winter Meeting and Nuclear Technology Expo, American Nuclear Society, San Diego CA. November 11-15, 2012.
• Frank J. Saglime III, Yaron Danon, Robert C. Block, Michael J. Rapp, Rian M. Bahran, Greg Leinweber, Devin P. Barry, Noel J. Drindak, and Jeffrey G. Hoole, “A system for differential neutron scattering experiments in the energy range from 0.5 to 20 MeV”, Nuclear Instruments and Methods in Physics Research Section A, 620, Issues 2-3, Pages 401-409, (2010).
• Frank J. Saglime III, Yaron Danon, Robert C. Block, Michael J.Rapp, and Rian M. Bahran, Devin P. Barry, Greg Leinweber, and Noel J. Drindak, "High Energy Neutron Scattering Benchmark of Monte Carlo Computations", International Conference on Mathematics, Computational Methods & Reactor Physics (M&C 2009), Saratoga Springs, New York, May 3-7, 2009, on CD-ROM, American Nuclear Society, LaGrange Park, IL (2009).
• Frank J. Saglime III, High Energy Neutron Differential Scattering Measurements For Beryllium And Molybdenum, PhD dissertation, Rensselaer Polytechnic Institute, Troy, NY 12180, June 2009.
• Frank J. Saglime III, Yaron Danon, Robert Block, "Digital Data Acquisition System for Time of Flight Neutron Beam Measurements", The American Nuclear Society’s 14th Biennial Topical Meeting of the Radiation Protection and Shielding Division, p. 368, Carlsbad New Mexico, USA. April 3-6, 2006.