The ground-state configuration of the N=157 nucleus 259No has been identified through α-γ coincidence and α-singles measurements. Three γ transitions were observed for the first time in the α decay of 259No, and its decay scheme was established. The neutron 9/2 + configuration was assigned to the ground state of 259No as well as to the 231.4 keV level in 255Fm. Ground-state deformations and neutron single-particle energies in Z=102 isotopes were calculated with the macroscopic-microscopic model. The 9/2+ orbital was calculated to be the highest among the five orbitals between the N=152 and 162 deformed shell gaps, which is consistent with the experimental one-quasiparticle energies in N=153 and 155 isotones, but is inconsistent with the present experimental result of the 9/2+ ground state at N=157. To reproduce the 9/2+ ground state at N=157, the order of the neutron orbitals should be different between the N=153 and 157 isotones.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics