Shape transition and pair phase transition together with their evolution on even 80∼86Zr isotopes

By using a microscopic sdIBM-2+2q. p. approach which is the accomplishment of the phenomenological core plus two-quasi-particle model and the experimental single-particle energies, the levels of the ground-band, γ-band and partial two-quasi-particle states on even 80-86Zr isotopes are successfully reproduced. The shape transition which transits from SU(3) symmetry to O(6) one, then to U(5) on for the isotopes is achieved. Based on the phenomenological model and microscopic approach, it has been deduced that no s-boson in the nucleus occupies breaking pair and aligning; and the minimum aligend energy required when one d-boson does is obtained. The threshold value explicitly indicates that along with the increase of neutron number, the evolvements from the two-quasi-proton states on 80Zr nucleus to the two-quasi-neutron states on 86Zr nucleus may take place in even Zr isotopes. (authors)