Ground-state bands of neutron-rich Th and U nuclei and implication of spherical shell closure at

Ishii, Tetsuro  ; Makii, Hiroyuki   ; Asai, Masato  ; Koura, Hiroyuki   ; Shigematsu, Soichiro*; Tsukada, Kazuaki  ; Toyoshima, Atsushi; Matsuda, Makoto  ; Makishima, Akiyasu*; Kaneko, Junichi*; Tome, Hayato; Hossain, I.*; Shizuma, Toshiyuki; Ichikawa, Shinichi; Kono, Toshiyuki*; Ogawa, Masao*

The ground-state bands of the neutron-rich Th and U nuclei were established up to spin 10 and 8, respectively, by in-beam -ray spectroscopy using the (O, Ne) two-proton pickup reaction with a U and a Pu target. Deexcitation rays in Th and U were identified by selecting the kinetic energies of Ne using Si - detectors. The excitation energies of the first 2 states in U and Pu isotopes have local minima at , suggesting the possibility that nuclei with have a spherical shell closure of . Calculation using the Koura-Yamada single-particle potential gives an energy gap of 1.8 MeV at for U.