In-beam $γ$-ray spectroscopy at the proton dripline: $^{40}$Sc

Abstract

We report on the first in-beam γ-ray spectroscopy of the proton-dripline nucleus 40 Sc using two-nucleon pickup onto an intermediate-energy rare-isotope beam of 38 Ca. The 9 Be( 38 Ca, 40 Sc+γ)X reaction at 60.9 MeV/nucleon mid-target energy selectively populates states in 40 Sc for which the transferred proton and neutron couple to high orbital angular momentum. In turn, due to angular-momentum selection rules in proton emission and the nuclear structure and energetics of 39 Ca, such states in 40 Sc then exhibit γ-decay branches although they are well above the proton separation energy. This work uniquely complements results from particle spectroscopy following charge-exchange reactions on 40 Ca as well as 40 Ti EC/β + decay which both display very different selectivities. The population and γ-ray decay of the previously known first (5 − ) state at 892 keV and the observation of a new level at 2744 keV are discussed in comparison to the mirror nucleus and shell-model calculations. On the experimental side, this work shows that high-resolution in-beam γ-ray spectroscopy is possible with new generation Ge arrays for reactions induced by rare-isotope beams on the level of a few µb of cross section.