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

A total of ten previously observed γ rays have been assigned to the N=Z+1 nucleus ⁶³Ga; these provide the first information on excited states reported in this neutron-deficient system. ⁶³Ga has been populated using the ⁴⁰Ca(²⁸Si, αp), ⁴⁰Ca(³²S, 2αp), and ⁴⁰Ca(²⁹Si, αpn) reactions at beam energies of 80–100 MeV. Particle-γ coincidence techniques provide a definitive identification of γ transitions in ⁶³Ga. An yrast-level scheme is proposed on the basis of charged-particle-γ, charged-particle-γ-γ, and neutron-γ-γ coincidences. Spin and parity assignments are based on neutron-gated γ-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^-)₁→(3/2^-)₁ transition in ⁶⁵Ga, resolving a disagreement between two previous measurements.