Neutron activation analysis: Gamma-ray spectra analysis of thin foils irradiated with high-energy neutrons

Abstract

iThemba LABS is participating in a joint research project to measure neutron-induced cross-sections for the (n, xn) reactions for various target materials. For neutron energies above 20 MeV, the (n, xn) set of reactions is becoming increasingly important for neutron fluence monitoring and spectra unfolding for future generation IV nuclear reactors. Test experiments commenced at the iThemba LABS facility with irradiations of target materials using quasi-monoenergetic neutron beams at high energies (above 40 MeV). These experiments are meant to evaluate the sensitivity of generating a clear γ-ray spectrum above the background level of the counting system. For this contribution, we report on the neutron activation analysis of the following target materials, 197Au and 169Tm using a quasi-monoenergetic neutron beam of about 90 MeV. The discussion focuses on calibrating the gamma-ray detector, and counting, and analyzing the gamma-ray spectra of the neutron-activated foils. The following reaction products were identified 194Au, 196Au, 198Au, 167Tm, and 168Tm. Using the background-corrected gamma-ray spectra, the activities of the reaction products were calculated with uncertainties ranging between 5 % and 30 %.