Rotational properties of the odd-Z transfermium nucleus 255Lr by a particle-number-conserving method in the cranked shell model
Experimentally observed ground state band based on the 1/2−[521] Nilsson state and the first exited band based on the 7/2−[514] Nilsson state of the odd-Z nucleus 255Lr are studied by the cranked shell model (CSM) with the paring correlations treated by the particle-number-conserving (PNC) method. This is the first time the detailed theoretical investigations are performed on these rotational bands. Both experimental kinematic and dynamic moments of inertia (J(1) and J(2)) versus rotational frequency are reproduced quite well by the PNC-CSM calculations. By comparing the theoretical kinematic moment of inertia J(1) with the experimental ones extracted from different spin assignments, the spin 17/2− → 13/2− is assigned to the lowest-lying 196.6(5) keV transition of the 1/2−[521] band, and 15/2− → 11/2− to the 189(1) keV transition of the 7/2−[514] band, respectively. The proton N = 7 major shell is included in the calculations. The intruder of the high-j low-Ω 1j15/2 (1/2−[770]) orbital at the high spin leads to band-crossings at ħω ≈ 0.20 (ħω ≈ 0.25) MeV for the 7/2−[514] α = −1/2 (α = +1/2) band, and at ħω ≈ 0.175 MeV for the 1/2−[521] α = −1/2 band, respectively. Further investigations show that the band-crossing frequencies are quadrupole deformation dependent.