Gamma Decay of Low-lying Levels inNb93

Abstract

Mean lifetimes for four levels in $^{93}\mathrm{Nb}$ have been measured by the Doppler-shift attenuation method. $\ensuremath{\gamma}$-ray angular distributions have been measured for the $\ensuremath{\gamma}$ decay of excited levels in $^{93}\mathrm{Nb}$ up to 1127 keV in excitation. The levels were excited by the $^{90}\mathrm{Zr}(\ensuremath{\alpha}, p\ensuremath{\gamma})^{93}\mathrm{Nb}$ reaction at a bombarding energy of 14.77 MeV. Spectra of $\ensuremath{\gamma}$ rays in coincidence with protons were obtained with a 55-${\mathrm{cm}}^{3}$ Ge(Li) detector. Spin assignments obtained from the present results for the low-lying positive-parity levels in $^{93}\mathrm{Nb}$ are in agreement with previous assignments. A ${J}^{\ensuremath{\pi}}$ of ${\frac{3}{2}}^{\ensuremath{-}}$ has been assigned to a level at 685 keV in excitation and a ${J}^{\ensuremath{\pi}}$ of ${\frac{5}{2}}^{\ensuremath{-}}({\frac{3}{2}}^{\ensuremath{-}})$ has been assigned to an 809-keV negative-parity level. $\ensuremath{\gamma}$-ray mixing ratios measured for the $\ensuremath{\gamma}$ decay of excited low-lying levels in $^{93}\mathrm{Nb}$ have been combined with lifetime measurements to calculate the electromagnetic transition strengths. The experimental $E2$ transition strengths are shown to be consistent with those predicted by a weak-coupling model.NUCLEAR REACTIONS $^{90}\mathrm{Zr}(\ensuremath{\alpha}, \mathrm{p}\ensuremath{\gamma})$, $E=14.77$ MeV; measured $\ensuremath{\tau}$, ${E}_{\ensuremath{\gamma}}$, $\mathrm{p}\ensuremath{\gamma}$ coin, ${I}_{\ensuremath{\gamma}}(\ensuremath{\theta})$, $\ensuremath{\delta}$. $^{93}\mathrm{Nb}$ deduced levels $J$, $\ensuremath{\pi}$, $\ensuremath{\Gamma}$.