The Westcott convention converted in the extended version of the modified Høgdahl convention
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In k0-NAA it is common practice to use the modified Høgdahl 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 Høgdahl convention. The benefit is that Høgdahl’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 Høgdahl flux parameters are presented.
KeywordsExtended Høgdahl Westcott review Effective resonance energy Resonance integral ENDF/B-VII.1
The author thanks Frans De Corte for the motivating discussions and comments during the journey in understanding Westcott’s paper. And is very grateful to the late András Simonits, who was also working on this topic, for Westcott’s revision from 1970 that finally clarified the last discrepancies.
- 1.De Corte F (1987) The k 0-standardization method: move to the optimization of neutron activation analysis. Habil. Thesis, Ghent University, BelgiumGoogle Scholar
- 2.Westcott CH (1960) Effective cross section values for well-moderated thermal reactor spectra. Atomic Energy of Canada Limited, Research and Development, Chalk River Laboratory, Ontario, Canada, AECL-1101/CRRP960 (November 1970)Google Scholar