Properties of high-spin states inNb91andZr91viaLi6-induced reactions

Abstract

The properties of high-spin states in $^{91}\mathrm{Nb}$ and $^{91}\mathrm{Zr}$ have been studied with the $^{88}\mathrm{Sr}(^{6}\mathrm{Li},3n)^{91}\mathrm{Nb}$ and $^{88}\mathrm{Sr}(^{6}\mathrm{Li},p2n)^{91}\mathrm{Zr}$ reactions. In-beam measurements with Ge(Li) and Si(Li) detectors of $\ensuremath{\gamma}$-ray excitation functions, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}$-ray angular distributions, and pulsed beam-$\ensuremath{\gamma}$ timing spectra were made to establish decay schemes, level energies, spin-parity assignments, $\ensuremath{\gamma}$-ray multipolarities, and isomeric lifetimes. All of the high-spin states involving the $\ensuremath{\pi}1{\mathrm{g}}_{\frac{9}{2}}$, $\ensuremath{\pi}2{\mathrm{p}}_{\frac{1}{2}}$, and $\ensuremath{\nu}2{\mathrm{d}}_{\frac{5}{2}}$ orbitals as well as other more complicated states were identified. In particular, the theoretically predicted isomeric states in $^{91}\mathrm{Nb}$ and $^{91}\mathrm{Zr}$ were found: the $|{(1{g}_{\frac{9}{2}})}^{2}2{p}_{\frac{1}{2}},{\frac{17}{2}}^{\ensuremath{-}}〉$ state in $^{91}\mathrm{Nb}$ is at 2035 keV with a $\ensuremath{\tau}=5.42\ifmmode\pm\else\textpm\fi{}0.18$ \ensuremath{\mu}sec, and the $|{(1{g}_{\frac{9}{2}})}^{2}2{d}_{\frac{5}{2}},{\frac{21}{2}}^{+}〉$ state in $^{91}\mathrm{Zr}$ is at 3167 keV with a $\ensuremath{\tau}=6.28\ifmmode\pm\else\textpm\fi{}0.20$ \ensuremath{\mu}sec. The experimental energy levels and $B(E2)$ values obtained for these nuclei as well as those of other $N=50 \mathrm{and} 51$ nuclei are compared with recent theoretical work of Gloeckner et al. The $E2$ effective charges for the mass-90 region are discussed.NUCLEAR REACTIONS $^{88}\mathrm{Sr}(^{6}\mathrm{Li},3n)$, $^{88}\mathrm{Sr}(^{6}\mathrm{Li},p2n)$, $E=34$ MeV, pulsed beam; measured $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence; deduced levels in $^{91}\mathrm{Nb}$ and $^{91}\mathrm{Zr}$; measured $\ensuremath{\gamma}(E, \ensuremath{\theta}, t)$; deduced ${J}^{\ensuremath{\pi}}$, ${T}_{\frac{1}{2}}$, branching ratio, $\ensuremath{\delta}(\frac{E2}{M1})$, $B(E2)$, effective charges. Natural target, Ge(Li) and Si(Li) detectors.