Contents lists available at ScienceDirect Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso Determination of k 0 and Q 0 for 74 Se, 113 In, 186 W and 191 Ir targets applying covariance analysis L.F. Barros, R.V. Ribeiro, M.S. Dias ∗ , M. Moralles, R. Semmler, I.M. Yamazaki, M.F. Koskinas Instituto de Pesquisas Energéticas e Nucleares (IPEN-CNEN/SP), Centro do Reator de Pesquisas - CRPq, C.P. 11049, Pinheiros, 05422-970, São Paulo SP, Brazil HIGHLIGHTS • Activation parameters k 0 and Q 0 were determined for 74 Se, 113 In, 186 W and 191 Ir. • The irradiation position was chosen where the neutron spectrum shape parameter α is very close to zero. • All partial uncertainties and correlations between parameters were considered. ARTICLE INFO Keywords: k 0 method Gamma-ray spectrometry Se In W Ir isotopes Neutron activation analysis Nuclear reactor ABSTRACT In the present work, the determinations of k 0 and Q 0 for 74 Se, 113 In, 186 W and 191 Ir targets were performed. The irradiations were conducted 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. The irradiation position was chosen where the neutron spectrum shape parameter α is very close to zero. For this reason, the correction to be applied for the determination of Q 0 is very close to one, thus improving the accuracy of the results. For each experiment, two irradiations were carried out in sequence: the frst one with bare samples and the second with a cadmium cover around the samples. All partial uncertainties were con- sidered, applying the covariance matrix methodology. The fnal results were compared with the literature. 1. Introduction There have been continued eforts to provide more accurate values of k 0 and Q 0 parameters in order to fulfll the Neutron Activation Analysis (NAA) user needs (e.g. Jaćimović and Stibilj, 2010; Lin and Von Gostomski, 2013; Chilian et al., 2014; Arboccò et al., 2014; Sneyers and Vermaercke, 2014; Stopic and Bennett, 2014; Trkov et al., 2015). At the same time, new statistical techniques have been introduced (Dias et al., 2010, 2011; Barros, 2018) to supply not only the overall un- certainties in these parameters but also their correlations. In the present study, 74 Se, 113 In, 186 W and 191 Ir targets were con- sidered. The irradiations were conducted 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. The irradiation position was chosen where the neutron spectrum shape parameter α is very close to zero. For this reason, the correction to be applied for the determi- nation of Q 0 is very close to one, improving the accuracy of the results. For each experiment, two irradiations were carried out in sequence: the frst with bare samples and the second with a cadmium cover around the samples. The reason for choosing 74 Se was to compare the results with De Corte and Simonits (2003), Jaćimović (Jaćimović and Stibilj, 2010), k 0 Database (k 0 Database, 2019), Sneyers and Vermaercke (2014) and Lin and Von Gostomski (2013). 113 In was selected in order to verify the infuence of overlapping wide low-energy absorption resonances, mainly for the determination of Q 0 (Kodeli and Trkov, 2007; Farina Arboccò et al., 2014); at the Second Research Coordination Meeting on the Reference Database for Neutron Activation Analysis (Firestone and Kellett, 2008) the value of k 0 for the reaction 186 W(n, γ) 187 W showed a discrepancy comparing the experimental value of the resonance in- tegral with the one calculated from diferential data. 191 Ir was chosen following the suggestion by Stopic (Stopic and Bennett, 2014) who recommended Q 0 should be determined separately for this isotope using reactors better suited for that purpose. This is the case of the present irradiation position where α is very close to zero. All partial un- certainties were considered, applying the covariance matrix metho- dology. https://doi.org/10.1016/j.apradiso.2019.108846 Received 14 January 2019; Received in revised form 25 July 2019; Accepted 6 August 2019 ∗ Corresponding author. E-mail addresses: msdias@ipen.br, maurosilvadias@gmail.com (M.S. Dias). Applied Radiation and Isotopes 154 (2019) 108846 Available online 09 August 2019 0969-8043/ © 2019 Elsevier Ltd. All rights reserved. T