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Title: Monte-Carlo Generation of Time Evolving Fission Chains

Abstract

About a decade ago, a computer code was written to model neutrons from their “birth” to their final “death” in thermal neutron detectors (3He tubes): SrcSim had enough physics to track the neutrons in multiplying systems, appropriately increasing and decreasing the neutron population as they interacted by absorption, fission and leakage. The theory behind the algorithms assumed that all neutrons produced in a fission chain were all produced simultaneously, and then diffused to the neutron detectors. For cases where the diffusion times are long compared to the fission chains, SrcSim is very successful. Indeed, it works extraordinarily well for thermal neutron detectors and bare objects, because it takes tens of microseconds for fission neutrons to slow down to thermal energies, where they can be detected. Microseconds are a very long time compared to the lengths of the fission chains. However, this inherent assumption in the theory prevents its use to cases where either the fission chains are long compared to the neutron diffusion times (water-cooled nuclear reactors, or heavily moderated object, where the theory starts failing), or the fission neutrons can be detected shortly after they were produced (fast neutron detectors). For these cases, a new code needs to bemore » written, where the underlying assumption is not made. The purpose of this report is to develop an algorithm to generate the arrival times of neutrons in fast neutron detectors, starting from a neutron source such as a spontaneous fission source (252Cf) or a multiplying source (Pu). This code will be an extension of SrcSim to cases where correlations between neutrons in the detectors are on the same or shorter time scales as the fission chains themselves.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1114717
Report Number(s):
LLNL-TR-642612
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 22 GENERAL STUDIES OF NUCLEAR REACTORS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Verbeke, Jerome M., Kim, Kenneth S., Prasad, Manoj K., and Snyderman, Neal J. Monte-Carlo Generation of Time Evolving Fission Chains. United States: N. p., 2013. Web. doi:10.2172/1114717.
Verbeke, Jerome M., Kim, Kenneth S., Prasad, Manoj K., & Snyderman, Neal J. Monte-Carlo Generation of Time Evolving Fission Chains. United States. https://doi.org/10.2172/1114717
Verbeke, Jerome M., Kim, Kenneth S., Prasad, Manoj K., and Snyderman, Neal J. 2013. "Monte-Carlo Generation of Time Evolving Fission Chains". United States. https://doi.org/10.2172/1114717. https://www.osti.gov/servlets/purl/1114717.
@article{osti_1114717,
title = {Monte-Carlo Generation of Time Evolving Fission Chains},
author = {Verbeke, Jerome M. and Kim, Kenneth S. and Prasad, Manoj K. and Snyderman, Neal J.},
abstractNote = {About a decade ago, a computer code was written to model neutrons from their “birth” to their final “death” in thermal neutron detectors (3He tubes): SrcSim had enough physics to track the neutrons in multiplying systems, appropriately increasing and decreasing the neutron population as they interacted by absorption, fission and leakage. The theory behind the algorithms assumed that all neutrons produced in a fission chain were all produced simultaneously, and then diffused to the neutron detectors. For cases where the diffusion times are long compared to the fission chains, SrcSim is very successful. Indeed, it works extraordinarily well for thermal neutron detectors and bare objects, because it takes tens of microseconds for fission neutrons to slow down to thermal energies, where they can be detected. Microseconds are a very long time compared to the lengths of the fission chains. However, this inherent assumption in the theory prevents its use to cases where either the fission chains are long compared to the neutron diffusion times (water-cooled nuclear reactors, or heavily moderated object, where the theory starts failing), or the fission neutrons can be detected shortly after they were produced (fast neutron detectors). For these cases, a new code needs to be written, where the underlying assumption is not made. The purpose of this report is to develop an algorithm to generate the arrival times of neutrons in fast neutron detectors, starting from a neutron source such as a spontaneous fission source (252Cf) or a multiplying source (Pu). This code will be an extension of SrcSim to cases where correlations between neutrons in the detectors are on the same or shorter time scales as the fission chains themselves.},
doi = {10.2172/1114717},
url = {https://www.osti.gov/biblio/1114717}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Aug 01 00:00:00 EDT 2013},
month = {Thu Aug 01 00:00:00 EDT 2013}
}