In-beam γ-ray spectroscopy at the proton dripline: 23Al

Abstract

We report on the first in-beam γ-ray spectroscopy of 23Al using two different reactions at intermediate beam energies: inelastic scattering off 9Be and heavy-ion induced one-proton pickup, 9Be(22Mg,23Al+γ)X, at 75.1 MeV/nucleon. A γ-ray transition at 1616(8) keV—exceeding the proton separation energy by 1494 keV—was observed in both reactions. From shell model and proton decay calculations we argue that this γ-ray decay proceeds from the core-excited 7/2+ state to the 5/2+ ground state of 23Al. The proposed nature of this state, [22Mg(21+)⊗πd5/2]7/2+, is consistent with the presence of a γ-branch and with the population of this state in the two reactions.