NECP-Atlas中热中子散射律数据生成模块的开发与验证

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

基于热中子散射理论,在核数据处理程序NECP-Atlas中开发了热中子散射律数据生成模块。在相干弹性散射中,去除了传统方法中的晶体立方近似和原子位置近似,采用各向异性位移参数(ADPs)方法得到考虑了不同原子位置和作用力方向影响的相干弹性散射律数据,使得相干弹性散射模型适用于任意结构晶体。运用有效宽度模型或自由气体模型考虑液体靶中的扩散效应,运用离散谐振子模型考虑多原子分子靶的分子内部振动,以及舍尔德近似考虑分子间的相干效应。通过对D 2O中D非弹性、LiH中H非相干弹性、金属Be相干弹性散射律数据的计算,证明了程序和方法的正确性。采用ADPs方法计算的金属Be相干弹性散射律数据与传统方法相比,精度最大提高约10%。ICSBEP基准题计算结果表明,采用ADPs方法获得的金属Be热散射截面,会使计算的有效增殖因数更接近实验基准值平均约60 pcm。

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 D 2O,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 k eff closer to experimental reference value,about 60 pcm on average.