Observation and spectroscopy of new proton-unbound isotopes 30ar and 29cl: an interplay of prompt two-proton and sequential decay

Abstract

Previously unknown isotopes 30Ar and 29Cl have been identified by measurement of the trajectories of their in-flight decay products 28S+p+p and 28S+p, respectively. The analysis of angular correlations of the fragments provided information on decay energies and the structure of the parent states. The ground states of 30Ar and 29Cl were found at 2.25+0.15−0.10 and 1.8±0.1 MeV above the two- and one-proton thresholds, respectively. The lowest states in 30Ar and 29Cl point to a violation of isobaric symmetry in the structure of these unbound nuclei. The two-proton decay has been identified in a transition region between simultaneous two-proton and sequential proton emissions from the 30Ar ground state, which is characterized by an interplay of three-body and two-body decay mechanisms. The first hint of a fine structure of the two-proton decay of 30Ar∗(2+) has been obtained by detecting two decay branches into the ground and first-excited states of the 28S fragment.