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Title: Monte Carlo Simulation for LINAC Standoff Interrogation of Nuclear Material

Abstract

The development of new techniques for the interrogation of shielded nuclear materials relies on the use of Monte Carlo codes to accurately simulate the entire system, including the interrogation source, the fissile target and the detection environment. The objective of this modeling effort is to develop analysis tools and methods-based on a relevant scenario-which may be applied to the design of future systems for active interrogation at a standoff. For the specific scenario considered here, the analysis will focus on providing the information needed to determine the type and optimum position of the detectors. This report describes the results of simulations for a detection system employing gamma rays to interrogate fissile and nonfissile targets. The simulations were performed using specialized versions of the codes MCNPX and MCNP-PoliMi. Both prompt neutron and gamma ray and delayed neutron fluxes have been mapped in three dimensions. The time dependence of the prompt neutrons in the system has also been characterized For this particular scenario, the flux maps generated with the Monte Carlo model indicate that the detectors should be placed approximately 50 cm behind the exit of the accelerator, 40 cm away from the vehicle, and 150 cm above the ground. This positionmore » minimizes the number of neutrons coming from the accelerator structure and also receives the maximum flux of prompt neutrons coming from the source. The lead shielding around the accelerator minimizes the gamma-ray background from the accelerator in this area. The number of delayed neutrons emitted from the target is approximately seven orders of magnitude less than the prompt neutrons emitted from the system. Therefore, in order to possibly detect the delayed neutrons, the detectors should be active only after all prompt neutrons have scattered out of the system. Preliminary results have shown this time to be greater than 5 ?s after the accelerator pulse. This type of system is illustrative of a host of real-world scenarios of interest to nonproliferation and homeland security. Due to the multistep procedure of the MCNPX/MCNP-PoliMi code system, the analysis of somewhat modular - meaning that changing details such as the detector type, position, or surroundings does not require a re-calculation of the source-target interactions. This feature allows for efficient parametric analysis of numerous system parameters without recomputing the constant source-target behavior. Such efficient analysis mechanisms could prove invaluable in the design and future deployment of an active interrogation detection system.« less

Authors:
 [1];  [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
931590
Report Number(s):
ORNL/TM-2007/079
TRN: US0803632
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; DELAYED NEUTRONS; DESIGN; DETECTION; DIMENSIONS; LINEAR ACCELERATORS; NEUTRONS; PARAMETRIC ANALYSIS; PROLIFERATION; PROMPT NEUTRONS; SECURITY; SHIELDING; SIMULATION; TARGETS; TIME DEPENDENCE

Citation Formats

Clarke, Shaun D, Flaska, Marek, Miller, Thomas Martin, Protopopescu, Vladimir A, and Pozzi, Sara A. Monte Carlo Simulation for LINAC Standoff Interrogation of Nuclear Material. United States: N. p., 2007. Web. doi:10.2172/931590.
Clarke, Shaun D, Flaska, Marek, Miller, Thomas Martin, Protopopescu, Vladimir A, & Pozzi, Sara A. Monte Carlo Simulation for LINAC Standoff Interrogation of Nuclear Material. United States. https://doi.org/10.2172/931590
Clarke, Shaun D, Flaska, Marek, Miller, Thomas Martin, Protopopescu, Vladimir A, and Pozzi, Sara A. 2007. "Monte Carlo Simulation for LINAC Standoff Interrogation of Nuclear Material". United States. https://doi.org/10.2172/931590. https://www.osti.gov/servlets/purl/931590.
@article{osti_931590,
title = {Monte Carlo Simulation for LINAC Standoff Interrogation of Nuclear Material},
author = {Clarke, Shaun D and Flaska, Marek and Miller, Thomas Martin and Protopopescu, Vladimir A and Pozzi, Sara A},
abstractNote = {The development of new techniques for the interrogation of shielded nuclear materials relies on the use of Monte Carlo codes to accurately simulate the entire system, including the interrogation source, the fissile target and the detection environment. The objective of this modeling effort is to develop analysis tools and methods-based on a relevant scenario-which may be applied to the design of future systems for active interrogation at a standoff. For the specific scenario considered here, the analysis will focus on providing the information needed to determine the type and optimum position of the detectors. This report describes the results of simulations for a detection system employing gamma rays to interrogate fissile and nonfissile targets. The simulations were performed using specialized versions of the codes MCNPX and MCNP-PoliMi. Both prompt neutron and gamma ray and delayed neutron fluxes have been mapped in three dimensions. The time dependence of the prompt neutrons in the system has also been characterized For this particular scenario, the flux maps generated with the Monte Carlo model indicate that the detectors should be placed approximately 50 cm behind the exit of the accelerator, 40 cm away from the vehicle, and 150 cm above the ground. This position minimizes the number of neutrons coming from the accelerator structure and also receives the maximum flux of prompt neutrons coming from the source. The lead shielding around the accelerator minimizes the gamma-ray background from the accelerator in this area. The number of delayed neutrons emitted from the target is approximately seven orders of magnitude less than the prompt neutrons emitted from the system. Therefore, in order to possibly detect the delayed neutrons, the detectors should be active only after all prompt neutrons have scattered out of the system. Preliminary results have shown this time to be greater than 5 ?s after the accelerator pulse. This type of system is illustrative of a host of real-world scenarios of interest to nonproliferation and homeland security. Due to the multistep procedure of the MCNPX/MCNP-PoliMi code system, the analysis of somewhat modular - meaning that changing details such as the detector type, position, or surroundings does not require a re-calculation of the source-target interactions. This feature allows for efficient parametric analysis of numerous system parameters without recomputing the constant source-target behavior. Such efficient analysis mechanisms could prove invaluable in the design and future deployment of an active interrogation detection system.},
doi = {10.2172/931590},
url = {https://www.osti.gov/biblio/931590}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Jun 01 00:00:00 EDT 2007},
month = {Fri Jun 01 00:00:00 EDT 2007}
}