Gamma production cross sections from 14-MeV neutron bombardment ofY89

Abstract

$\gamma$ decays of levels in ${}_{}{}^{88}{}_{}{}^{}\mathrm{Y}$ and ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ have been observed with a Ge(Li) spectrometer following 14.1-MeV neutron bombardment of natural yttrium metal. Prompt and delayed (> 50 nsec) radiations were separated by pulsing the neutron source. Following the reaction ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}\mathrm{}(n,2n)\mathrm{}-{}_{}{}^{88}{}_{}{}^{}\mathrm{Y}$, delayed $\gamma$ rays of 442 and 232 keV are ascribed to the decay sequence $8^{+}$ (674 keV) → $5^{-}$ (232) → $4^{-}$ (0) and a 393-keV $\gamma$ ray to the transition $1^{+}$ (393) → $4^{-}$ (0). A delayed 909-keV radiation corresponds to the decay of the first excited state of ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$. Cross sections were determined with an uncertainty of ± 11% for the delayed radiations and ± 30% for the remainder. A statistical-model calculation for the ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}\mathrm{}(n,2n)\mathrm{}{}_{}{}^{88}{}_{}{}^{}\mathrm{Y}$ reaction reproduces the observed cross sections only if the $\gamma$ branching ratios in ${}_{}{}^{88}{}_{}{}^{}\mathrm{Y}$ are taken from experiment, and in particular, the ${\left(g_{\frac{9}{2}}\right)}^2$ multiplet is included.