Systematics of isomeric configurations inN=77odd-Zisotones near the proton drip line

Abstract

The systematics of the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ and $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{s}_{1/2}$ isomeric configurations was studied for the odd-Z $N=77$ isotones near the proton drip line. The isomeric decays in $^{140}\mathrm{Eu}$, $^{142}\mathrm{Tb}$, $^{144}\mathrm{Ho}$, and $^{146}\mathrm{Tm}$ were measured by means of x-ray, \ensuremath{\gamma}-ray, and charged particle spectroscopy at the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility (ORNL). The spin and parity of ${I}^{\ensuremath{\pi}}={8}^{+}$ and ${5}^{\ensuremath{-}}$ were deduced for the isomers in $^{140}\mathrm{Eu}$ and $^{142}\mathrm{Tb}$. New decay schemes were established, and the half-lives of the ${8}^{+}$ isomers were measured to be 302(4) ns for $^{140m2}\mathrm{Eu}$ and 25(1) \ensuremath{\mu}s for $^{142m2}\mathrm{Tb}$. No evidence for the expected ${1}^{+}$ ground-state was found in the $^{144}\mathrm{Ho}$ decay data. The proton-emission from $^{146}\mathrm{Tm}$ was restudied. Five proton transitions were assigned to two proton-emitting states. The half-lives of 198(3) ms and 68(3) ms and the spin and parity values of ${I}^{\ensuremath{\pi}}={10}^{+}$ and ${5}^{\ensuremath{-}}$ were established for $^{146m}\mathrm{Tm}$ and $^{146\mathrm{gs}}\mathrm{Tm}$, respectively. For the first time for an odd-odd nucleus, the interpretation of the observed decay properties and structure of the proton-emitting states was made by accounting for deformation and proton and neutron coupling to the core excitations. A complex wave-function structure was obtained, with dominating components of $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ for the ${10}^{+}$ isomer and $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{s}_{1/2}$ for the ${5}^{\ensuremath{-}}$ ground state.