Towards a methodology for bulk sample neutron activation analysis

The main challenge in large sample neutron activation analysis (LSNAA) is the determination of neutron self-shielding and gamma ray self-attenuation corrections. After these corrections are determined, the analysis proceeds as in normal neutron activation analysis (NAA), as if the sample were infinitely small. In this paper, these corrections are calculated using the MCNP code for different standard sample geometries with different diameters. Modelling studies for LSNAA using an external neutron beam were performed. An analytical formula for the correction factors for neutron self-shielding and gamma ray self-attenuation is derived. The correction factors as well as flux parameters are calculated analytically. The analytical formula is verified using the MCNP code. All of the calculated parameters were tabulated and graphed. From the calculated data, other unknown material parameters could be obtained based on tabulated data or graphs. This method is a direct and easy method to perform large sample neutron activation analysis without complex calculations. In addition, for the user who does not have good experience with codes such as MCNP, she/he can use the chart or the tabulated information to define their unknown sample with the required information for the LSNAA experiment.