Neutron one-quasiparticle states in Fm populated via the decay of No

Asai, Masato  ; Tsukada, Kazuaki  ; Haba, Hiromitsu*; Ishii, Yasuo; Ichikawa, Takatoshi*; Toyoshima, Atsushi; Ishii, Tetsuro  ; Nagame, Yuichiro ; Nishinaka, Ichiro; Kojima, Yasuaki*; Sueki, Keisuke*

Excited states in Fm populated via the decay of No are studied in detail through - coincidence and fine structure measurements. Spin-parities and neutron configurations of the excited states in Fm as well as the ground state of No are definitely identified on the basis of deduced internal conversion coefficients, lifetimes of transitions, rotational-band energies built on one-quasiparticle states, and hindrance factors of transitions. It is found that the excitation energy of the 1/2[620] state in =151 isotones increases with the atomic number, especially at 100, while that of the 1/2[631] state decreases at =100. Energy systematics of the one-quasiparticle states in the =151 isotones are discussed in terms of the evolution of nuclear deformation involving the hexadecapole and hexacontatetrapole deformations.