Spectroscopy of excited states of unbound nuclei ${}^{30}$Ar and ${}^{29}$Cl

Abstract

Several states of proton-unbound isotopes ${}^{30}$Ar and ${}^{29}$Cl were investigated by measuring their in-flight decay products, ${}^{28}$S+proton+proton and ${}^{28}$S+proton, respectively. A refined analysis of ${}^{28}$S-proton angular correlations indicates that the ground state of ${}^{30}$Ar is located at $2.45_{-0.10}^{+0.05}$ MeV above the two-proton emission threshold. The theoretical investigation of the ${}^{30}$Ar ground state decay demonstrates that its mechanism has the transition dynamics with a surprisingly strong sensitivity of the correlation patterns of the decay products to the two-proton decay energy of the ${}^{30}$Ar ground state and the one-proton decay energy as well as the one-proton decay width of the ${}^{29}$Cl ground state. The comparison of the experimental ${}^{28}$S-proton angular correlations with those resulting from Monte Carlo simulations of the detector response illustrates that other observed ${}^{30}$Ar excited states decay by sequential emission of protons via intermediate resonances in ${}^{29}$Cl. Based on the findings, the decay schemes of the observed states in ${}^{30}$Ar and ${}^{29}$Cl were constructed. For calibration purposes and for checking the performance of the experimental setup, decays of the previously-known states of a two-proton emitter ${}^{19}$Mg were remeasured. Evidences for one new excited state in ${}^{19}$Mg and two unknown states in ${}^{18}$Na were found.

17 pages, 16 figures