Nuclear structure studies in the medium mass (A ≈ 70) region

The in-beam γ-ray studies on several nuclei in A ≈ 70 region, have revealed highly collective band structures of the following types: 1) ground state band, 2) one or two even spin positive parity bands with 8⁺ as band head, 3) odd and even spin negative parity bands, 4) ΔJ = 1 even parity bands with 2⁺ as band heads, 5) deformed bands built on the first excited 0⁺ states. Not all these types of bands have been observed in all of the nuclei in this mass region. The even spin positive parity bands with 8⁺ as band head and the negative parity bands can be understood in terms of rotational alignment model. The Interacting Boson Model calculations reproduce the negative parity bands and the ΔJ = 1 even parity bands with 2⁺ as band head. Both these models have to be further investigated as to the validity of them in describing nuclei in the mass region A ≈ 70. Recent dynamic deformation model calculations of Kumar support the shape coexistence picture for ⁷²Se, which explains the deformed bands built on the first excited 0⁺ states.