Development of Monte Carlo code for Coincidence Prompt Gammaray Neutron Activation Analysis

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Development of Monte Carlo code for Coincidence
Prompt Gamma-ray Neutron Activation Analysis

• Xiaogang Han, Robin P. Gardner

Center for Engineering Applications of
Radioisotopes _at_ NCSU
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Agenda

• Overview (PGNAA and CPGNAA)
• Monte Carlo code CEARCPG
• Benchmark Experiments
• Conclusion

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Overview-PGNAA
Pb
S
Ca
Hg
Excited level
Pb
S
C
Hg
O
Mg
Pb
C
S
C
O
Mg
Ground level
Ca
Neutron Source
Ca
S
Hg
S
O
Bulk sample
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Overview-PGNAA

• Advantages
• Nondestructive
• Simultaneous
• In Situ
• Quantitative
• sensitive to the entire periodic table.
• shape of the sample are relatively unimportant.

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Overview-PGNAA

• Disadvantages
• PGNAA has an inherently large background
• Interference from the neutron excitation source.
• Natural background
• Structure materials
• Detector activation (NaI)
• Summing and pulse pile-up effect

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Overview-PGNAA
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Overview-PGNAA

• Improvement introduce gamma gamma coincidence
  technique (CEAR and BNC, Budapest Neutron Center)
• Advantages of gamma gamma coincidence technique
• Increase the signal to noise ratio
• Reduce the interference of background
• Eliminate the hydrogen prompt gamma-ray peak

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Overview-Coincidence measurement
1.17 MeV
1.332 MeV
2.502 MeV
NaI activation
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Overview-Coincidence measurement
K
Th
U
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Overview-MC work

• CEARPGA I, the first specific Monte Carlo code
  publicly reported to implement MCLLS algorithm
  for PGNAA analyzer
• Big weight problem
• Detector response function
• Library spectrum (natural background, NaI
  activation)
• CEARPGA II
• Interpolation
• NaI activation spectra

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Physics neutron reaction

• Neutron capture reaction
• Neutron elastic scattering reaction
• Neutron inelastic scattering reaction
• Thermal neutron scattering
• Free gas model

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Physics neutron reaction

• Neutron Capture reaction

12C
13C
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Physics neutron reaction
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Physics photon reaction

• Photon Pair-production reaction
• Electron and positron deposit energy locally
• Annihilation photons are tracked independently
• Photoelectron reaction
• Photon-Electron deposit energy locally
• Compton scattering reaction
• Angular distribution Klein-Nishina formula

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CEARCPG-introduction

• Why we need to develop MC code
• No existence MC code for coincidence PGNAA
  application
• Specific MC code can be used to optimize the
  coincidence PGNAA application design. It also can
  be used to predict and check the experiment
  results.
• It can be used to develop new algorithm for
  coincidence PGNAA analysis

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CEARCPG-introduction

• The first specific Monte Carlo Code that can be
  used for prompt gamma sampling and for prompt
  gamma coincidence spectra simulation.
• Coded in Fortran 95 on windows platform.
• Dynamic memory allocation
• Can be used to analyze 42 elements, 97 isotopes
  and easy to update.
• Neutron energy is from 10-11MeV to 20 MeV. Gamma
  energy is from 1 keV to 20 MeV
• Most of CEARCPG cards take the same form as those
  used in MCNP.
• Modularized code. Easy to implement to other MC
  code
• General geometry package
• Detailed physics model
• Variance reduction techniques

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CEARCPG-introduction

• CEARCPG-Geometry
• General geometry package treats an arbitrary
  3-dimensional configuration of user-defined
  materials in geometric cell bounded by first or
  second-degree surface
• Compatible with MCNP. Visual editor can be used
  to design and check the user-defined geometry.

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CEARCPG-introduction

• CEARCPG-Variance reduction techniques

• Neutron
• Stratified sampling
• Russian roulette
• Truncated Exponential pdf
• Rejection method
• Splitting

• Photon
• Russian roulette
• Energy cutoff
• Truncated Exponential pdf
• Rejection method

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CEARCPG-introduction
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CEARCPG-introduction
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CEARCPG-introduction
paraffin wax
Sample
Detector 1
Detector 2
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CEARCPG-introduction
paraffin wax
Sample
Detector 2
Detector 1
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Benchmark Experiments

• ETI prototype. Coal sample Simulation and fitting
• Pure sulfur sample. Experiment, simulation and
  fitting
• Pure mercury sample. Experiment, simulation and
  fitting

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Benchmark Experiments

• ETI prototype

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Benchmark Experiments
1
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Benchmark Experiments
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Benchmark Experiments
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Benchmark Experiments

• Experiment 2 pure sulfur sample

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Benchmark Experiments
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Benchmark Experiments
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Benchmark Experiments
3.220
5.420
0.841
7.799
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Benchmark Experiments

• Experiment 3 pure mercury sample

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Benchmark Experiments
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Benchmark Experiments
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Benchmark Experiments
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Optimization of CPGNAA application
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Conclusion

• Coincidence PGNAA is a new developing technique
  and has already been approved that it can
  significantly reduce the interference and
  increase the accuracy of PGNAA analysis
• Code CEARCPG is the first specific MC code which
  can be used to simulate the coincidence spectra.
• Several benchmark experiments have been carried
  out to check the simulation results of CEARCPG.
  The results indicate that this code is accurate
  and very useful in the design for coincidence
  PGNAA device.

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