The new neutron-rich rare-earth isotopes ${}^{159}\mathrm{Pm}$, ${}^{162}\mathrm{Sm}$, and ${}^{166}\mathrm{Gd}$ produced in the proton-induced fission of ${}^{238}\mathrm{U}$ were identified using the JAERI on-line isotope separator (JAERI-ISOL) coupled to a gas-jet transport system. The half-lives of ${}^{159}\mathrm{Pm}$, ${}^{162}\mathrm{Sm}$, and ${}^{166}\mathrm{Gd}$ were determined to be 1.5 ± 0.2, 2.4 ± 0.5, and 4.8 ± 1.0 s respectively. The partial decay scheme of ${}^{166}\mathrm{Gd}$ was constructed from $\gamma \gamma$-coincidence data. A more accurate half-life value of 25.6 ± 2.2 s was obtained for the previously identified isotope ${}^{166}\mathrm{Tb}$. The half-lives measured in the present study are in good agreement with the theoretical predictions calculated by the second generation of the gross theory with the atomic masses evaluated by Audi and Wapstra.

• Received 17 November 2004

DOI:https://doi.org/10.1103/PhysRevC.71.067302