β decay of neutron-richCa53−56

Abstract

\ensuremath{\beta}-decay properties of neutron-rich Ca isotopes have been obtained. Half-life values were determined for the first time for $^{54}\mathrm{Ca}$ ($86\ifmmode\pm\else\textpm\fi{}7$ ms), $^{55}\mathrm{Ca}$ ($22\ifmmode\pm\else\textpm\fi{}2$ ms), and $^{56}\mathrm{Ca}$ ($11\ifmmode\pm\else\textpm\fi{}2$ ms). The half-life of $230\ifmmode\pm\else\textpm\fi{}60$ ms deduced for $^{53}\mathrm{Ca}$ is significantly longer than reported previously, where the decay chain $^{53}\mathrm{K}$ \ensuremath{\rightarrow} $^{53}\mathrm{Ca}$ \ensuremath{\rightarrow} $^{53}\mathrm{Sc}$ was considered. A delayed \ensuremath{\gamma} ray with an energy of 247 keV was identified following \ensuremath{\beta} decay of $^{54}\mathrm{Ca}$ and is proposed to depopulate the ${1}_{1}^{+}$ level in $^{54}\mathrm{Sc}$. The \ensuremath{\beta}-decay properties compare favorably with the results of shell-model calculations completed in the full $\mathit{pf}$ space with the GXPF1 interaction. The half-lives of the neutron-rich Ca isotopes are also compared with gross \ensuremath{\beta}-decay theory. The systematic trend of the neutron-rich Ca half-lives is consistent with the presence of a subshell gap at $N=32$.