Isomer Ratios forY87,87mand the Spin Dependence of the Nuclear Level Density

Abstract

Isomeric cross-section ratios have been measured for the following nuclear reactions in which the ${\mathrm{Y}}^{87,87m}$ isomeric pair is produced: ${\mathrm{Rb}}^{85}(\alpha , 2n)$, ${\mathrm{Sr}}^{86}(d, n)$, ${\mathrm{Sr}}^{87}(d, 2n)$, and ${\mathrm{Sr}}^{88}(d, 3n)$. The results are interpreted in terms of the angular momentum dependence of the nuclear level density. Statistical-model calculations based on the predictions of various theoretical formalisms are presented. Ambiguities in the calculation related to level density parameters and the multipolarity of the emitted radiation are discussed. The calculations are in qualitative agreement with experiment, although there are some difficulties in interpreting the level density parameters obtained. The effect of competing proton and alpha-particle channels on the isomer ratios for reactions in which neutrons are emitted has been investigated. The competition does not appreciably alter the isomer ratios in the particular case under discussion.