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

TL;DR

This study presents the first in-beam gamma-ray spectroscopy of the proton-dripline nucleus $^{40}$Sc, revealing new energy levels and demonstrating the effectiveness of advanced gamma-ray detection techniques with rare-isotope beams.

Contribution

It introduces a novel experimental approach to study $^{40}$Sc using in-beam gamma-ray spectroscopy with high-resolution Ge arrays, providing new insights into its nuclear structure.

Findings

Observation of a new level at 2744 keV in $^{40}$Sc

Confirmation of the known 892 keV state and its decay properties

Demonstration of high-resolution gamma-ray spectroscopy with rare-isotope beams

Abstract

We report on the first in-beam $\gamma$-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$+\gamma$)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 $\gamma$-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/$\beta^+$ decay which both display very different selectivities. The population and $\gamma$-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 $\gamma$-ray spectroscopy is possible with new generation Ge arrays for reactions induced by rare-isotope beams on the level of a few $\mu$b of cross section.