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

We report on the first in-beam gamma-ray spectroscopy of Al-23 using two different reactions at intermediate beam energies: inelastic scattering off Be-9 and heavy-ion induced one-proton pickup, Be-9(Mg-22,Al-23 + gamma)X, at 75.1 MeV/nucleon. A gamma-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 gamma-ray decay proceeds from the core-excited 7/2(+) state to the 5/2(+) ground state of Al-23. The proposed nature of this state, [Mg-22(2(1)(+)) circle times pi d(5/2)](7/2)+, is consistent with the presence of a gamma-branch and with the population of this state in the two reactions. (C) 2008 Elsevier B.V. All rights reserved.