In-beam gamma -ray spectroscopy of the N=Z+1 nucleus 63Ga.

Abstract

A total of ten previously observed \ensuremath{\gamma} rays have been assigned to the N=Z+1 nucleus $^{63}\mathrm{Ga}$; these provide the first information on excited states reported in this neutron-deficient system. $^{63}\mathrm{Ga}$ has been populated using the $^{40}\mathrm{Ca}$${(}^{28}$Si, \ensuremath{\alpha}p), $^{40}\mathrm{Ca}$${(}^{32}$S, 2\ensuremath{\alpha}p), and $^{40}\mathrm{Ca}$${(}^{29}$Si, \ensuremath{\alpha}pn) reactions at beam energies of 80--100 MeV. Particle-\ensuremath{\gamma} coincidence techniques provide a definitive identification of \ensuremath{\gamma} transitions in $^{63}\mathrm{Ga}$. An yrast-level scheme is proposed on the basis of charged-particle-\ensuremath{\gamma}, charged-particle-\ensuremath{\gamma}-\ensuremath{\gamma}, and neutron-\ensuremath{\gamma}-\ensuremath{\gamma} coincidences. Spin and parity assignments are based on neutron-gated \ensuremath{\gamma}-ray angular distributions, directional correlation with oriented nuclei ratios and systematics. Nine new energy levels are identified in addition to the previously known ground state, with the highest level at an excitation energy of 7.7 MeV. The results are interpreted in terms of the relevant single-particle orbitals and the systematics of the neighboring nuclei. In addition, a new determination has been made of the E2/M1 mixing ratio for the (5/${2}^{\mathrm{\ensuremath{-}}}$${)}_{1}$\ensuremath{\rightarrow}(3/${2}^{\mathrm{\ensuremath{-}}}$${)}_{1}$ transition in $^{65}\mathrm{Ga}$, resolving a disagreement between two previous measurements.