β-decay half-lives of new neutron-rich rare-earth isotopes Pm159,Sm162, and Gd166

The new neutron-rich rare-earth isotopes Pm159, Sm162, and Gd166 produced in the proton-induced fission of U238 were identified using the JAERI on-line isotope separator (JAERI-ISOL) coupled to a gas-jet transport system. The half-lives of Pm159, Sm162, and Gd166 were determined to be 1.5 ± 0.2, 2.4 ± 0.5, and 4.8 ± 1.0 s respectively. The partial decay scheme of Gd166 was constructed from γγ-coincidence data. A more accurate half-life value of 25.6 ± 2.2 s was obtained for the previously identified isotope Tb166. 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.