Influence of the effective mass on the relative neutron density distribution inside a large sample in prompt-gamma neutron activation analysis

A Monte Carlo study was carried out to determine the influence of the effective scattering mass (Me) of the atoms on the neutron density profile inside and outside the sample illuminated by a thermal neutron beam as in large-sample prompt-gamma neutron activation analysis (LS-PGNAA). From theory it is known that the spatial neutron density distribution (n(r)) inside a large sample is not the same for atoms with the same macroscopic scattering and absorption cross-section (Σs and Σa) but different Me, due to anisotropic scattering at low Me. The probability of neutron absorption in the sample was found to be the same for materials with equal Σs and Σa but different Me, even though the neutron density distribution in the sample was found to change slightly. In view of typical sample, collimator and detector dimensions, it is concluded that Me does not need to be taken into account in a correction method for neutron self-shielding in LS-PGNAA. (author)