Prompt gamma-ray spectroscopy of Fm and the N=152 deformed shell gap

Fmの線分光法とN=152変形シェルギャップ

Orlandi, R.  ; 牧井 宏之   ; 西尾 勝久   ; 廣瀬 健太郎  ; 浅井 雅人  ; 塚田 和明  ; 佐藤 哲也   ; 伊藤 由太   ; 洲嵜 ふみ  

Orlandi, R.; Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Asai, Masato; Tsukada, Kazuaki; Sato, Tetsuya; Ito, Yuta; Suzaki, Fumi

Nuclear shell structure is predicted to give rise to long-lived super heavy elements (SHEs) in the Island of Stability (IoS), roughly located around proton number Z=114-126 and neutron number N=176-184, with the most probable magic numbers of Z=114 or 120 and N=184. Orbits stemming from the IoS are lowered by deformation and affect the structure of neutron-rich actinide nuclei near Z=100, and N=152 and 162, where energy gaps appear in the deformed single-particle spectrum. The heavy actinides located in proximity of these deformed gaps thus provide a link to the IoS, but their nuclear structure is still poorly known. To improve the current knowledge of the structure of Fm (at the crossing of Z=100 and N=152 gaps) and of neighboring isotopes, an in-beam -ray experiment was carried out at the JAEA Tandem accelerator. An accelerated O beam impinged on a Cf target, and several isotopes of Cf, Es, Fm, Md and No were produced via multi-nucleon transfer reactions. The species and excitation energy of the heavy nuclei produced were identified on a event-by-event basis by detecting the light ejectiles with an array of Silicon telescopes. Four Germanium detectors and four large-volume LaBr(Ce) scintillators were used to detect the rays. In the experiment, Fm was successfully produced and -ray transitions emitted by Fm observed. Preliminary results will be presented.