ENDF-VI库次级中子数据的能量守恒问题

Energy-balance Problem of Secondary Neutrons of ENDF-VI Data

在评价核数据库ENDF VI版的出射粒子能量分布数据(即文档5)中,一些核素在阈能附近的次级中子能量分布大多采用简单的近似方法描述,例如三角形分布或矩形分布.这些简单的近似描述,将导致产生散射矩阵的"双峰"现象,或使平均次级中子能量过大而产生负KERMA(ki neticenergyreleaseinmaterials)因子.针对这两个现象,通过细致的分析,讨论了这些现象的产生原因,并试对相关数据做一定的修正,以改善次级中子分布的能量守恒问题.

In file 5 of ENDFVI, the arbitrary tabulated function (LF=1) was applied to some threshold reactions of some nuclides. The energy distribution of secondary spectrum was given approximately as a triangular shape or rectangular shape at the threshold energy for some nuclides. The triangular shape distributions would cause twopeaked energy distribution near the threshold energy, which must affect the group transfer matrix. The rectangular shape make the E′n too large, that may lead to a negative neutron KERMA(kinetic energy release in materials) factor. This will affect almost all of the integral quantities of the neutronics calculation. In this paper, we will discuss the reason of these abnormal behaviors, and how to improve the energy balance to eliminate the problem.