Isomer spectroscopy using actinide targets

Sugiyama, Koichi*; Go, Shintaro*; Tomimatsu, Taro*; Kai, Tamito*; Nagae, Daisuke*; Ishibashi, Yuichi*; Matsunaga, Sotaro*; Nagata, Yuto*; Nishibata, Hiroki*; Washiyama, Kohei*; Sakaguchi, Satoshi*; Morita, Kosuke*; Orlandi, R.   ; Nishio, Katsuhisa   ; Makii, Hiroyuki   ; Hirose, Kentaro  ; Ito, Yuta   ; Suzaki, Fumi  ; Sato, Tetsuya   ; Tsukada, Kazuaki  ; Asai, Masato  ; Shizuma, Toshiyuki*; Ideguchi, Eiji*; Pham, T. T.*; Niwase, Toshitaka*

We have successfully performed in-beam gamma-ray spectroscopy using the isomer-scope technique to study excited-state structure of neutron-rich heavy-actinide nuclei. The neutron-rich heavy-actinide nuclei were produced in the multinucleon-transfer reactions with a Cm target and O projectiles accelerated with the JAEA tandem accelerator. Projectile-like scattered particles were detected with Si E-E telescopes placed at the backward angle, and target-like scattered particles of isomers were caught by an annular aluminum plate placed at about 60-mm downstream from the target. Four Ge detectors and 4 LaBr detectors were placed at the periphery of the aluminum plate, and detected gamma rays from the isomers. Gamma rays emitted from the actinide isomers were successfully observed with a good sensitivity owing to the tungsten shield placed between the target and the detectors.