The Westcott convention converted in the extended version of the modified Høgdahl convention

Abstract

In k0-NAA it is common practice to use the modified Hogdahl convention for the description of (n, γ) activation. This convention is based on the principle that the activation cross-section in the thermal neutron range is following a 1/v shape, which results in an activation rate is independent of the speed distribution of the neutron density. For some isotopes, this is not the case. We call these isotopes “non-1/v”. For these nuclides, the activation rate in k0-NAA theory is described by the Westcott convention. Westcott uses a Maxwellian thermal neutron energy distribution comprised in a neutron temperature dependent “g”-factor. For the activation by epithermal neutrons a “s”-factor is defined. In this paper, the original Westcott convention is converted into an extension of the Hogdahl convention. The benefit is that Hogdahl’s flux parameters can be used. The epithermal flux description defined by Westcott is used to calculate extended QE’s with their appropriate effective resonance energies, Er. Since Westcott flux descriptions are neutron temperature dependent, the QE’s and Er’s are as well. All the data needed for the evaluation of concentrations for Lu, Eu and Yb based on their non-1/v nuclides using the standard Hogdahl flux parameters are presented.