Abstract
For accuracy improvement of neutron activation analysis and neutron capture cross sections, bias effects are investigated on g- and s-factors in the Westcott convention. As origins of biases, a joining function shape, neutron temperature, and sample temperature have been investigated. Biases are quantitatively deduced for two 1/v isotopes (197Au, 59Co) and six non-1/v isotopes (241Am, 151Eu, 103Rh, 115In, 177Hf, 226Ra). The s-factor calculated with a joining function deduced recently by a detailed Monte Carlo simulation is compared to s-factors calculated with traditional joining functions by Westcott. The results show the bias induced by the sample temperature is small, in the order of 0.1% for the g-factor and in the order of 1% for the s-factor. On the other hand, the bias size induced by a joining function shape for the s-factor depends significantly on both isotopes and neutron temperature. As a result, the reaction rates are also affected significantly. The bias size for the reaction rate is given in the case of an epithermal neutron index r = 0.1, for the eight isotopes.
Highlights
Academic Editor: Marco Di LuzioReceived: 31 May 2021Accepted: 13 July 2021Published: 16 July 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil-Neutron activation analysis (NAA) using well-thermalized neutrons is a powerful tool utilized in various application fields
The energy spectrum of well-thermalized neutrons is approximated to be the sum of two components, a Maxwellian distribution corresponding to neutron temperature Tn and an epithermal dE/E flux distribution cut off at a suitable lower limit of energy
Bias effects have been investigated on the g- and s-factors in the Westcott convention
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil-. The energy spectrum of well-thermalized neutrons is approximated to be the sum of two components, a Maxwellian distribution corresponding to neutron temperature Tn and an epithermal dE/E flux distribution cut off at a suitable lower limit of energy This flux notation is known as the Westcott convention [1] and is widely utilized in NAA. The systematic effect on the s-factor induced by a change in a joining function from a unit step function was studied for re-evaluation of neutron capture cross section of 241 Am measured by a neutron activation method [10]. This paper studies in detail the bias on the s-factor and the reaction rate induced by the joining function form ∆4H. A bias effect by sample temperature might be noticeable for isotopes with resonances around the cut-off energy of the joining function. Neutron self-absorption correction is known to be an important bias [13], this correction is outside the scope of this work
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