Deformation and magicity in heavy actinides; First observation of the ground-state rotational band of Fm

Orlandi, R.   ; Asai, Masato  ; Makii, Hiroyuki   ; Nishio, Katsuhisa   ; Hirose, Kentaro  ; Tsukada, Kazuaki  ; Sato, Tetsuya   ; Ito, Yuta   ; Suzaki, Fumi  ; Nagame, Yuichiro* ; Ishii, Tetsuro ; Andreyev, A. N.; Okada, Kazuki; Kasamatsu, Yoshitaka*; Toyoshima, Atsushi*; Nishinaka, Ichiro*; 14 of others*

The ground-state rotational band of Fm ( = 100, = 152) was investigated using two different experimental setups at the JAEA Tandem Accelerator Laboratory. The first five -ray transitions of the ground-state rotational band were observed for the first time. The new data revealed that Fm possesses the lowest first excited state energy, 41.88(16) keV, and the largest kinematic moment of inertia compared to neighboring isotopes in this region. These unique properties provide strong evidence for deformed shell gaps at = 100 and = 152, revealing that Fm is a deformed doubly magic nucleus.