Elsevier

Nuclear Physics A

Volume 355, Issue 1, 2 March 1981, Pages 228-260
Nuclear Physics A

In-beam study of 80Kr; Quasiparticle excitations in nuclei around mass 80

https://doi.org/10.1016/0375-9474(81)90140-8Get rights and content

Abstract

The excited states in 80Kr have been studied in the reactions 77Se(α, n), 78Se(α, 2n), 80Se(α, 4n) and 65Cu(18O, p2n) by using in-beam γ-ray spectroscopy. In addition to γγ-coincidences, excitation functions and angular distributions, linear polarization of γ-rays and conversion electrons were also measured. All together, 32 levels have been identified up to spin 14 at an excitation energy of 6.7 MeV in 80Kr. For 21 of these levels the mean lifetime could be determined by Doppler shift methods and by the pulsed-beam γ-timing method. The B(E2) values of 30–60 W.u., derived for many transitions, indicate strong collectivity and the existence of several band structures is suggested. Above 2.5 MeV 2-quasiparticle (qp) excitations become important. The excitation energies of 80Kr and its neighbours 77, 78, 79Kr, 77Br and 81Rb have been analysed in terms of the cranked shell model. In 78,80Kr two-proton excitations have been found to be responsible for the observed band crossing. Quasiparticle excitations strongly influence the pairing and stabilize the deformation. The anomalies in the negative-parity bands of 81Rb and 77Br are interpreted as a crossing of a 3qp and a 1qp band and the relatively low frequency of the crossing point is ascribed to the blocking effect.

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