Development and Verification of Thermal Neutron Scattering Law Data Producing Module in Nuclear Data Processing Code NECP-Atlas

Based on the theory of thermal neutron scattering, the thermal neutron scattering law data producing module was implemented in the nuclear data processing code NECP-Atlas. In the coherent elastic scattering, the cubic approximation and the atomic site approximation in the conventional method were removed. The anisotropic displacement parameters (ADPs) method was used to obtain the accurate coherent elastic scattering law data considering the influence of the different atomic positions and the direction of the forces, which makes the coherent scattering model suitable for any crystal structure. The effective width model or the free gas model was used to consider the diffusion effect in the liquid target. The discrete oscillator model was used to consider the internal vibration of the polyatomic molecular target, and the Sk-ld approximation was used to consider the inter-molecular coherence effect in liquid target. D in D₂O, H in LiH and metal beryllium were selected to verify the new sab_calc module. Compared with the conventional method, the accuracy of the coherent elastic scattering law data of metal beryllium calculated by ADPs method is improved by about 10%. The numerical results of ICSBEP benchmarks show that metal beryllium using ADPs method makes the calculated keff closer to experimental reference value, about 60 pcm on average.