Decay of Neutron-Rich Mn Nuclides and Deformation of Heavy Fe Isotopes

Abstract

The use of chemically selective laser ionization combined with $\ensuremath{\beta}$-delayed neutron counting at CERN/ISOLDE has permitted identification and half-life measurements for 623-ms ${}^{61}\mathrm{Mn}$ up through 14-ms ${}^{69}\mathrm{Mn}$. The measured half-lives are found to be significantly longer near $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}40$ than the values calculated with a quasiparticle random-phase-approximation shell model. Gamma-ray singles and coincidence spectroscopy has been performed for ${}^{64,66}\mathrm{Mn}$ decays to levels of ${}^{64,66}\mathrm{Fe}$, revealing a significant drop in the energy of the first ${2}^{+}$ state in these nuclides that suggests an unanticipated increase in collectivity near $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}40$.