Ground-state configuration of the N = 157 nucleus 259 No

The ground-state configuration of the N = 157 nucleus No-259 has been identified through alpha-gamma coincidence and alpha-singles measurements. Three gamma transitions were observed for the first time in the alpha decay of No-259, and its decay scheme was established. The neutron 9/2(+)[615] configuration was assigned to the ground state of No-259 as well as to the 231.4 keV level in Fm-255. Ground-state deformations and neutron single-particle energies in Z = 102 isotopes were calculated with the macroscopic-microscopic model. The 9/2(+)[615] 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(+)[615] ground state at N = 157. To reproduce the 9/2(+)[615] ground state at N = 157, the order of the neutron orbitals should be different between the N = 153 and 157 isotones. DOI: 10.1103/PhysRevC.87.014332