β-decay half-lives of new neutron-rich isotopes 167,168Tb and levels in 167,168Dy

Abstract

$\ensuremath{\beta}$-decay half-lives of new neutron-rich isotopes ${}^{167}\mathrm{Tb}$ and ${}^{168}\mathrm{Tb}$ produced in the 20 MeV proton-induced fission of ${}^{238}\mathrm{U}$ have been determined to be 19.4(27) s and 8.2(13) s, respectively, using a gas-jet coupled on-line isotope separator. The present half-lives and those of the recently identified nuclei ${}^{159}\mathrm{Pm},$ ${}^{161}\mathrm{Sm},$ ${}^{165}\mathrm{Gd},$ ${}^{166}\mathrm{Tb}$ were compared with theoretical predictions. The recent calculation by the gross theory with the new one-particle strength functions shows quite good agreement with the experimental half-lives. Excited states of the daughter nuclides ${}^{167}\mathrm{Dy}$ and ${}^{168}\mathrm{Dy}$ have been established for the first time. Level energies of the first ${2}^{+}$ states in even-even Dy isotopes were found to show an irregular behavior at ${}^{164}\mathrm{Dy}$ and increasing deformation toward the neutron midshell around $N\ensuremath{\approx}104$.