New Approximate Orientation Averaging of the Water Molecule Interacting with the Thermal Neutron

Exactly describing the time of thermal neutron collisions with water molecules, orientation averaging is performed by an exact method (EOA_K) and four approximate methods (two well known and two less known). Expressions for the microscopic scattering kernel are developed. The two well-known approximate orientation averaging methods are Krieger-Nelkin (K-N) and Koppel-Young (K-Y). The results obtained by one of the two proposed approximate orientation averaging methods agree best with the corresponding results obtained by EOA_K. The largest discrepancies between the EOA_K results and the results of the approximate methods are obtained using the well-known K-N approximate orientation averaging method.