Applications of IBM-3 to the Z ∼ N ∼ 40 nuclei

The nuclei with N ∼ Z ∼ 40 are characterized by large deformation but γ-soft spectra with low values of the energy ratio E41+∗E21+∗ ∼ 2.5 and E41+∗ ∼ E2γ+∗. Since N ∼ Z, we have applied the Interacting Boson Model with Isospin (IBM-3) to these nuclei. Using a complete diagonalization program for IBM-3 hamiltonians, we have investigated the shape transitions from A = 80 to 90 of the Sr and Zr isotopes. To describe the γ-soft features, we assume the O(5) symmetry for the hamiltonian. As the deformation increases with A→80, the calculated energy levels are in good agreement with the experimental data. In particular, B(E2: J1+ → (J − 2)1+) of the ground band as well as the energy spectra of the ground and the γ bands of 80Sr are close to the predictions of the O(6) limit of the IBM. The splitting of the scissors motions by isospin is also discussed. We have shown that IBM-3 is applicable to the strongly deformed γ-soft nuclei at A ∼ 80.