Abstract
The k0 values of 6 non-1/v nuclides (152Eu, 152mEu, 154Eu, 177Lu, 192Ir and 194Ir) were determined using the extended Høgdahl formalism at the research reactor FRM II with very high f values. Standards were irradiated in 4 channels at different local temperatures between 40 °C and 55 °C measured using temperature sensitive irreversible labels. A good agreement with the recommended values was found for 152Eu, 154Eu and 177Lu using the original g(Tn) factors by Gryntakis, however, the k0 values for 152mEu in this work were 7% higher. New k0 values were also determined using the g(Tn) factors by Van Sluijs. Differences up to 6% were found for Eu isotopes compared with the recommended values. The recommended k0 values for 192Ir and 194Ir could be confirmed using g = 1. The theoretical k0 values for 177Lu were calculated using new nuclear data. They are up to 6% less than the recommended values. The present k0 values determined in this work showed a similar trend. The influence of different g(Tn) factors on the determination of the k0 values was investigated.
Highlights
The k0 NAA method was first developed with the Høgdahl convention, which treated the activation with both thermal and epithermal neutrons as a temperature independent static process describing very well the (n,γ)reactions of most nuclides with cross sections varying as 1/v (v is the neutron velocity) in the thermal neutron energy region [1, 2]
For a few so-called non-1/v nuclides, a modification using the Westcott convention [3] with consideration of the influence of the neutron temperature on the cross sections was introduced in the 1990s [4, 5], while the definition of the k0 factor including the cross section at a neutron velocity of 2200 m s−1
Lutetium was suggested since the beginning, because the thermal neutron capture cross section of the reaction 176Lu(n,γ)177Lu varies very strongly with the neutron temperature
Summary
The k0 NAA method was first developed with the Høgdahl convention, which treated the activation with both thermal and epithermal neutrons as a temperature independent static process describing very well the (n,γ)reactions of most nuclides with cross sections varying as 1/v (v is the neutron velocity) in the thermal neutron energy region [1, 2]. Lutetium was suggested since the beginning, because the thermal neutron capture cross section of the reaction 176Lu(n,γ)177Lu varies very strongly with the neutron temperature. In this case, the recommended k0 values of 177Lu were calculated using atomic and nuclear data, including the cross section at the neutron velocity of 2200 m s−1, from the 1980s [2]. At FRM II, a method using irreversible thermometer labels was developed to measure the temperature at the irradiation positions in situ [7] and applied to determine the k0 values of some non-1/v nuclides in this work
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