Band structures of 76Se and 78Se

Abstract

Band structures of 76Se and 78Se have been studied with the 74,76Ge(α, 2nγ) 76,78Se reactions by using a variety of in-beam γ-techniques : γ-ray singles spectra, γ-ray excitation functions, γ- γ- t coincidences, γ-ray angular distributions and γ-ray linear polarizations. Spins and parities have been assigned uniquely for many new levels in 76Se and 78Se and four bands have been identified in both nuclei: (i) the ground-state band, (ii) a positive-parity ΔJ = 1 band built on the second 2 + state (γ-vibrational band), (iii) a negative-parity Δ J = 2 band built on the 3 − state (octupole band) and (iv) a ΔJ = 2 band built on the high-lying J = 4 state. In addition, the second 8 + and 10 + states, which are possibly the lowest members of a band, have been found in both nuclei. Systematics of the band structures obtained are discussed. Level energies of the band members and B(E2) ratios for some of the inter-band transitions between γ- and ground-state bands have been calculated with the proton-neutron interacting boson model IBM-2 and a reasonable agreement with the present data has been obtained.