The shape evolution and shape coexistence phenomena in neutron-rich nuclei at
N≈60, including Kr, Sr, Zr, and Mo isotopes, are studied in the
covariant density functional theory (DFT) with the new parameter set PC-PK1.
Pairing correlations are treated using the BCS approximation with a separable
pairing force. Sharp rising in the charge radii of Sr and Zr isotopes at N=60
is observed and shown to be related to the rapid changing in nuclear shapes.
The shape evolution is moderate in neighboring Kr and Mo isotopes. Similar as
the results of previous Hartree-Fock-Bogogliubov (HFB) calculations with the
Gogny force, triaxiality is observed in Mo isotopes and shown to be essential
to reproduce quantitatively the corresponding charge radii. In addition, the
coexistence of prolate and oblate shapes is found in both 98Sr and
100Zr. The observed oblate and prolate minima are related to the low
single-particle energy level density around the Fermi surfaces of neutron and
proton respectively. Furthermore, the 5-dimensional (5D) collective Hamiltonian
determined by the calculations of the PC-PK1 energy functional is solved for
98Sr and 100Zr. The resultant excitation energy of 02+ state and
E0 transition strength ρ2(E0;02+→01+) are in rather good
agreement with the data. It is found that the lower barrier height separating
the two competing minima along the γ deformation in 100Zr gives
rise to the larger ρ2(E0;02+→01+) than that in 98Sr.Comment: 1 table, 11 figures, 23 page