Recoil distance lifetime measurements in82Kr

Abstract

+4The lifetimes z = 124 _+ 12, 6 _ 2 and 3 80 • 100 ps of the E~ (U) = 3.46(8 +), 2.92(6 +) and 3.04(6-) MeV states, respectively, populated by the reaction 76Ge(12C, ~2n) were measured with the recoil distance method. In addition upper lifetime limits were obtained for nine states. The measured lifetimes and energies indicate a band crossing at about U = 8 +, probably arising from the alignment of two g9/2 neutrons. For the 3.04 MeV 6-state as a second member of a band built on the 2.65 MeV 4-state, the measured lifetime points to a two-quasiparticle configuration. The positive-parity states have been discussed in the frame of the interacting boson approximation, nuclear field theory and the cranked shell model.Nuclear Reactions: 76Ge(12C,~2n), E=42-52MeV; measured Er, ty, recoil distance Doppler shift. 82Kr levels deduced z. Enriched targets.

Yrast transition strengths in85Rb and85Sr

“…1 and 5), it is the 17/2+--* 13/2 + E2 strengths which are most drastically affected by the backbending. The situation is thus very similar to that recently observed in the neighboring even-even nuclei 82Kr and 84Sr [16] where the 8 + ~ 6 + transition energy is much reduced, but the effect of band crossing is best visible in the 6 + ~ 4 + E2 transition strengths. c) A survey of ali known positive-parity states in vg, 81, 83, 85Rb is given in Fig.…”

“…High spin states in 85Rb and 8SSr were excited via the reactions 76Ge(lZC, p2n) and 76Ge(12C, 3n), respectively. The third strong reaction channel, 76Ge(I2C, e2n)82Kr, has also been analysed and the results have been published separately [16]. Figure 1 shows the 7-ray intensity flux of the reaction 76Ge(12C, p2n) along the yrast cascade in 85Rb as determined from ?-ray singles spectra which were recorded at 45 MeV beam energy and 0~= 55 ~ to the beam.…”

Lifetime measurements in70Se and72Se

“…It is obvious that each nucleus behaves in a different way, with B(E2) values being constant in 68Ge up to P=8 + and rising steeply in 72Se. The decreasing B(E2) values in 7~ agree, however, with those of the ground band in S4Sr [28,29] where the pronounced backbend between P = 6 + and 8 § has been attributed to (2qp)g9/z neutron alignment [30]. Figure 8b displays Ix(e)) plots of the bands in 68Ge, V~ and 72Se and illustrates the different degrees of backbending.…”

Decay of three-particle high spin states in85Y

“…This is illustrated in Fig. 8 were the yrast E2 strengths in 84Sr [2,6] and the isobares 85y, 85Sr and 85Rb [18] are compared with different models. Clearly, the cluster vibrational approach labelled SMCC which involves more than one valence nucleon [33] gives a better description of these E2 transitions.…”

“…The yrast lines of the N=46 nuclei, isotones of the nucleus 8sy to be discussed here, offer some very good examples for this behaviour: the lowest two-quasi-particle configurations in 82Kr and 84Sr have been associated with the alignment of the neutrons in the g9/2 orbit [2][3][4][5][6][7], while (3qp) structures involving the g9/2 and f5/2 orbits have been suggested to appear as yrast states in 83Rb [8]. The crossing of the respective ground bands with these intruders usually leads to strong reductions of the collective E2 strengths as well as level orderings different from that typical for collective rotations.…”