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

The use of chemically selective laser ionization combined with β-delayed neutron counting at CERN/ISOLDE has permitted identification and half-life measurements for 623-ms ⁶¹Mn up through 14-ms ⁶⁹Mn. The measured half-lives are found to be significantly longer near N0ex0ex=0ex0ex40 than the values calculated with a quasiparticle random-phase-approximation shell model. Gamma-ray singles and coincidence spectroscopy has been performed for 64,66Mn decays to levels of 64,66Fe, revealing a significant drop in the energy of the first 2⁺ state in these nuclides that suggests an unanticipated increase in collectivity near N0ex0ex=0ex0ex40.