Evidence of boson cut-off in the aligned band in 79Rb

Recoil distance lifetime measurements in82Kr

“…Further evidence for the g9/2 proton character of the S-band in 7SKr comes from the spectrum of the g9/2 decoupled proton band in 79Rb for which no backbending has been observed [19], because the S-band is blocked. From these considerations, one may expect that the strong reductions of the E2 strengths for the 3.46(8+)--+2.92(6 ~ ) and 2.92(6+)-,1.82(4+)MeV yrast transitions in S2Kr is also caused by proton alignment.…”

“…In a geometrical picture, the nuclear shape seems to change smoothly from a nearly axially symmetric rotator (/~(74Kr)~0.35) to a triaxial rotator or ?,-vibrational structure (/~(82Kr)~0. 19). In addition to the collective picture of 78, SOKr ' two-quasiparticle excitations have very recently been introduced as the expla-* Work supported by Deutsches Btmdesministerium far Forschung und Technologie i Permanent address: University of Helsinki, Finland nation of the backbending and reduced E2 transition probabilities of the yrast band at U~8 § [2].…”

Yrast transition strengths in85Rb and85Sr

“…4, it has already been stated by Bucurescu et al [4] that the approach of the triaxial rotor plus quasiparticle does not work for the yrast cascade of 85Sr if the core parameters are taken from the 86Sr or 84Sr ground bands, This curve is labelled AR(SSSr) in Fig. 4 [18].…”

“…The measured ratio B(E2, 13/2 --* 9/2)/B(E2, 2 -~ 0) = 0.96 [12] thus proves that even the lowest transition in the 85Rb cascade does not follow the rotational alignment model, but agrees with a simple weak-coupling approach. The decrease of yrast transition energies and strengths for increasing spin value observed in both [3,4]. The curves labelled AR refer to asymmetric rotor plus quasi-particle calculations [3,4,20]; the 8SRb values have been extrapolated from the calculations performed in 8XRb.…”

“…In spite of this considerable polarisation effect, the rotational aligned scheme applies to fairly high spin values as proven by the energies and E2 strengths. Convincing examples are the yrast spectra in 79Rb and 81Rb studied recently by Panqueva et al [3,4]; energies and lifetimes of these bands have been established up to P=29/2 + and 21/2 +, respectively. In the heavier Kr and Rb isotopes, i.e.…”