$\beta$ decay of neutron-rich $^{53--56}$Ca
P. F. Mantica, R. Broda, H. L. Crawford, A. Damaske, B. Fornal, A. A. Hecht, C. Hoffman, M. Horoi, N. Hoteling, R. V. F. Janssens, J. Pereira, J. S. Pinter, J. B. Stoker, S. L. Tabor, T. Sumikama, W. B. Walters, X. Wang, and S. Zhu

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

© 2008 The American Physical Society.