多群核数据中角分布出负的处理

Correction of Negative Angular Distributions in Multigroup Nuclear Data

多群核数据中,次级中子角分布一般以勒让德(Legendre)多项式展开的形式给出。展开阶数有限时,在某些角度区域角分布可能出现非物理的负值。最大熵方法利用已知的有限阶Legendre展开系数,得到合理的非负角分布。利用最大熵方法修正出负的角分布,制作了适用蒙特卡罗输运程序(MCNP)的ACE格式多群核数据。通过临界基准实验计算,验证了最大熵角分布处理方法的可靠性。

The angular distribution of the secondary neutron is typically represented as a truncated Legendre series expansion. Limited terms of the expansions may result in some non-physical negative regions for highly anisotropic scattering. The positive representation of the scattering angular distribution is produced by the maximum entropy method from the truncated Legendre series. The positive angular distributions are convert to multigroup nuclear data in ACE format available for MCNP. The reliability of the maximum entropy method for correcting the angular distribution is checked by the calculations of criticality benchmark experiment.