Proton Radioactivity from Highly Deformed Nuclei

Abstract

Proton radioactivity from ${}^{141}\mathrm{Ho}$ and ${}^{131}\mathrm{Eu}$ has been identified. The ${}^{141}\mathrm{Ho}$ proton transition has an energy ${E}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1169(8)\mathrm{keV}$, a half-life ${t}_{1/2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4.2(4)\mathrm{ms}$, and is assigned to the decay of the ${7/2}^{\ensuremath{-}}[523]$ Nilsson state. The ${}^{131}\mathrm{Eu}$ transition has an energy ${E}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}950(8)\mathrm{keV}$ and a half-life of 26(6) ms, consistent with decay from either the ${3/2}^{+}[411]$ or ${5/2}^{+}[413]$ Nilsson orbital. The proton decay rates deviate significantly from calculations assuming spherical configurations, and thus indicate the onset of large deformations in the region of the proton drip line below $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}69$.