Endf-vi Of The Secondary Neutron Spectrum Energy Conservation

As well known, in the file 5 of ENDF-VI, the energy distribution of secondary neutron are represented by various analytical formulations.When the energy distribution are represented by arbitrary tabulated function (LF=1), some approximate descriptions (e.g. simple triangular shape or rectangular shape) of the energy distribution are applied near the threshold for some nuclides. It was found that the simple triangular shape distribution would cause "two-peaked" energy distribution near the threshold energy, which must affect the group transfer matrix. The rectangular shape wouldmake the E'_n too large, which can violate conservation of energy and may lead anegative neutron KERMA (Kinetic Energy Release in Materials) factor.When the energy distribution of secondary neutron are represented by evaporation spectrum (LF=9), care must be taken in describing the nuclear temperature near the threshold. The large nuclear temperature evaluation would violate conservation of energy, and may lead a negative neutron KERMA factor.In this paper, we will discuss the reason of these abnormal behaviors, and give some recommendation to modify the related data in the ENDF-VI(or other nuclear data library, e.g. CENDL-2 etc.), to improve the energy balance to eliminate the problem.