Previously unknown isotopes ${}^{30}\mathrm{Ar}$ and ${}^{29}\mathrm{Cl}$ have been identified by measurement of the trajectories of their in-flight decay products ${}^{28}\mathrm{S}+p+p$ and ${}^{28}\mathrm{S}+p$, 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 ${}^{30}\mathrm{Ar}$ and ${}^{29}\mathrm{Cl}$ were found at $2.25_{-0.10}^{+0.15}$ and $1.8\pm 0.1\mathrm{MeV}$ above the two- and one-proton thresholds, respectively. The lowest states in ${}^{30}\mathrm{Ar}$ and ${}^{29}\mathrm{Cl}$ 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 ${}^{30}\mathrm{Ar}$ 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 ${}^{30}{\mathrm{Ar}}^{*}(2^{+})$ has been obtained by detecting two decay branches into the ground and first-excited states of the ${}^{28}\mathrm{S}$ fragment.

• Received 6 August 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.202501