Characterization of neutron flux spectra in irradiation sites of MNSR reactor using the Westcott-formalism for the k0 neutron activation analysis method.

For the general applicability of the k0-NAA method to deal with "non-l/v" (n,gamma) reaction nuclides, the modified spectral index r(alpha) square root (Tn/T0) and g(Tn) factor for monitoring neutron temperature Tn for the inner and outer irradiation sites of the Ghana MNSR reactor (GHARR-1) were measured using the Cd-ratio method. Using the measured Cd ratio for lutetium and the modified spectral index, the reduced resonance integral of lutetium s0,Lu was also calculated. The computed result of 1.64 was in good agreement with the reported value of 1.67. Based on the assumption that the definitions of reaction rates in the Westcott-formalism and in Nisle's unified formulation are equal, a theoretical verification of the accuracy of the measured modified spectral indices for our data and those reported in the literature for other research reactors was carried out. Employing 197Au, 96Zr and 94Zr as "1/v" monitors, the theoretical values which depend on the choice of the monitor, followed the trend for measured values of the sub- to epi-cadmium flux ratio f for nine irradiation sites of four different research reactors. The computed and experimental modified spectral indices for the different flux ratios associated with irradiation sites within the range 18.8-152 fitted well to a simple exponential relationship. Calculated and measured data are in good agreement when appropriate correction factors are used.