Neutron Decay of Isobaric Analog Resonances inZr90

Abstract

Excitation functions and angular distributions of the $\gamma$ radiation from ${}_{}{}^{89}{}_{}{}^{}\mathrm{Zr}$ following the reaction ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}(p, n)$ have been measured with a 56-${\mathrm{cm}}^3$ Ge(Li) detector in the range from 5.4- to 7.8-MeV bombarding energy. At 6.00-, 6.16-, 7.28-, and 7.45-MeV bombarding energy, resonances in several neutron channels were observed which were attributed to isobaric analog states in the compound system ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$. From an analysis of the 6.16-MeV $1^{-}$ resonance in terms of Robson's theory, the level shift $\Delta =86\mathrm{}$ keV was obtained which was compared with an estimate derived from the spreading width of this resonance. New states in ${}_{}{}^{89}{}_{}{}^{}\mathrm{Zr}$ were identified at 1834-, 2081-, 2130-, 2220-, 2298-, 2389-, 2570-, and 2610-keV excitation energy. From a Hauser-Feshbach analysis of the $\gamma$-ray excitation functions and angular distributions, the spins of a number of these states and mixing ratios of $\gamma$-ray transitions were found. Evidence is given for a weak coupling multiplet of a $g_{\frac{9}{2}}$ neutron hole coupled to the 2.18-MeV $2^{+}$ state in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$.