Development of a non-invasive method for the determination of the macroscopic neutron cross sections of a sample matrix in large-sample prompt-gamma neutron activation analysis

In order to correct for neutron self-shielding in large-sample prompt gamma NAA, a method has been developed to determine the macroscopic scattering and absorption cross sections, i.e., Σa and Σs, using four Cu flux monitors placed around the sample. With Monte Carlo computations, the neutron densities throughout the sample and the resulting and the corresponding self-shielding factor as calculated from the Σa and Σs as obtained through the Cu monitors were compared to the true values. The derived Σa and Σs were found to be sufficiently accurate as long as Σt = Σa + Σs was less than 0.6 cm−1 and Σs/Σt was greater than 0.1.