Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains

Abstract

The proton-unbound argon and chlorine isotopes have been studied by measuring trajectories of their decay-in-flight products by using a tracking technique with microstrip detectors. The proton ($1p$) and two-proton ($2p$) emission processes have been detected in the measured angular correlations ``heavy-fragment''+$p$ and ``heavy-fragment''+$p+p$, respectively. The ground states of the previously unknown isotopes $^{30}\mathrm{Cl}$ and $^{28}\mathrm{Cl}$ have been observed for the first time, providing the $1p$-separation energies ${S}_{p}$ of $\ensuremath{-}0.48(2)$ and $\ensuremath{-}1.60(8)$, MeV, respectively. The relevant systematics of $1p$- and $2p$-separation energies have been studied theoretically in the $\mathrm{core}+p$ and $\mathrm{core}+p+p$ cluster models. The first-time observed excited states of $^{31}\mathrm{Ar}$ allow one to infer the $2p$-separation energy ${S}_{2p}$ of 6(34) keV for its ground state. The first-time observed state in $^{29}\mathrm{Ar}$ with ${S}_{2p}=\ensuremath{-}5.50(18)$ MeV can be identified as either a ground state or an excited state according to different systematics.