Preliminary measurements of k0 values for W-186

Abstract

There are various methods of neutron activation analysis, one of these is the k0 Method for quantitative reactor Neutron Activation Analysis (NAA). The k0-NAA procedure is nowadays widely used in numerous laboratories performing NAA all over the world. Among these reactions, 186W(n, )187W can be considered important because it can be used for a W concentration measurements. The irradiations were performed at position 24A, near the core of the IEA-R1 4.5 MW swimming-pool nuclear research reactor of the Instituto de Pesquisas Energéticas e Nucleares (IPEN-CNEN/SP – Nuclear and Energy Research Institute), in São Paulo, Brazil. Two irradiations were carried out in sequence, using two sets of samples: the first with a cadmium cover around the samples and the second without, in a total of three data sets with and without Cd cover performed in 2014 and 2015. The activity measurements were carried out in an HPGe gamma-ray spectrometer. Standard sources of 152Eu, 133Ba, 60Co and 137Cs supplied by the IAEA were used in order to obtain the HPGe gamma-ray peak efficiency as a function of the energy. The covariance matrix methodology was applied to all uncertainties involved. The preliminary values of k0 for 186W(n, )187W reaction for the gamma transition energy of 479.53 keV was 3.17x10-2(5), for 618.77 keV was 9.08x10-3(15) and for 685.77 keV was 3.88x10-2(6). These preliminary values for k0 have been compared with the literature.