6. Discussion and conclusion

Up to present, from the literature overview, the available data of neutron self-shielding factors are almost for the study of resonance neutron self-shielding correction Gres which is considered only in the energy region of primary resonance peak of reaction cross-section, but in NAA the thermal and epithermal neutron (or effective) self-shielding correction factor should be taken into account. Although the research topic on neutron self-shielding has been considered for a long history, the available resources for neutron activation analysis (INAA) applications are still limited in both respects of numerical data and computational tools. The previously published values, calculations and measurements, are mainly for the cases of resonance neutron selfshielding, and information is still lacking for the cases of thermal and epithermal neutron selfshielding that are needed in INAA with different standard foil and sample materials.

The MCNP5 code has been applied for exact simulation of neutron self-shielding correction factors of Gth, Gres and Gepi for activation foils of Au-97, Co-59, Mn-55 and W-186. The experimental configurations were simulated for the real condition of a reactor-based neutron activation experiment in which the irradiation channel can be described as a cylindrical isotropic neutron sources with sample flat to the channel axis. The three case studies of neutron energy spectrum: (1) the Maxwellian distribution with average energy of 0.025 eV was applied for thermal neutrons, (2) the pure 1/E distribution in energy range from 0.55 eV to 0.2 MeV was implemented for epithermal neutrons, and (3) the primary resonance energy peaks for resonance neutron spectrum. The results of simulated data with different foil thickness are presented in Tables 1 and 2.
