On the irregularities in the band structures of ⁷⁸Kr

Using in-beam gamma -ray spectroscopy techniques experimental information on the presence of two-quasiparticle components in the band structures of ⁷⁸Kr has been derived. The observation of a second 10⁺ state decaying by a fast M1 transition of B(M1, 10₂⁺ to 10₁⁺)=0.8(4) Wu to the 10⁺ yrast level gives strong evidence for a band crossing between the collective ground-state band and a two-quasiparticle band. The residual interaction between these configurations has been estimated to be V(10⁺)=130+or-10 keV. The configuration mixing also provides an explanation for the decrease of the B(E2) values in the yrast sequence above the 8⁺ level.