An update to the computation of the Goudsmit-Saunderson distribution in MCNP ?? version 6.2

Dixon, David A.¹ 

[1] Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

关键词: electron transport Goudsmit-Saunderson;   

DOI  :  10.2172/1330070
RP-ID  :  LA-UR--16-27959
PID  :  OSTI ID: 1330070

学科分类：数学（综合）

美国|英语

来源: SciTech Connect

【 摘 要 】

To demonstrate how the number of terms used to compute the Goudsmit- Saunderson distribution impacts results, we study a thin foil problem where the outgoing angular distribution is observed for 20-MeV electrons. The foil thickness is roughly 1.5 times the default substep size for a 20-MeV electron in gold ( 2.8e^-3 cm). Therefore, for the default substep size, electrons are guaranteed to undergo at least one collision before encountering a boundary (at which point an approximation is applied). In theory, one can improve the accuracy of the MCNP6.2 electron transport method by reducing the substep size. How- ever, one must assume that the underlying data is valid. We show that when a user reduces the substep size, the angular distribution observed is di erent than expected. The primary reason being that the underlying data was not computed using a sufficient number of terms. We also show that the distribution is recovered when the number of terms is increased from hundreds to thousands. Here, we showed that stabilizing the underlying angular deflection distributions used in transport improves simulation results, particularly, when default parameters are adjusted such that the substep size is reduced. Stabilization is achieved by adding more terms when computing the Goudsmit-Sanderson distribution.