Four-quasiparticle alignments in66Ge

Abstract

The neutron-deficient nucleus 66 Ge was populated at high spin in two experiments using the reaction 40 Ca(32 S,␣2p) at beam energies of 105 and 95 MeV. In the first experiment, a self-supporting 40 Ca target was used, while a gold-backed target of similar thickness was used in the second experiment. ␥ rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The level scheme of 66 Ge was extended up to EϷ18 MeV and I ϭ(23 Ϫ). Above angular momentum 10 ϩ , we found two sequences, connected by energetically staggered ⌬Iϭ1 M 1 transitions. The total Routhian surface calculations describe 66 Ge at lower spins as a ␥-soft nucleus having a moderate deformation of ␤ 2 Ϸ0.23, while a triaxial deformation is predicted for the band structures above I ϭ10 ϩ. To our knowledge, this is the first observation of staggered M 1 transitions in a deformed four-quasiparticle (g 9/2 2)(g 9/2 2) structure.

Observation of aγband based on a two-quasiparticle configuration inGe70

“…The observed alignment at ω ≈ 0.50 MeV for band B1, shown in Fig.7, is attributed to g 2 9/2 neutron alignment, consistent with predictions in previous work [12,15,24]. In comparison to neighboring isotopes, the observed crossing in band B1 of 70 Ge occurs slightly earlier (by ≈ 0.16 MeV) than the observed alignments in 66−68 Ge [25,28]. This might be attributed to the shape change in crossing around rotational frequency ≈ 0.53 MeV (Fig.…”

“…An important observation in the present work is identification of a new band structure B2 which arises from forking of the ground state band at 6 + state. Such band structures with forking have also been observed earlier in neighboring nuclei 66−68 Ge [25][26][27][28]. The band B2 is extended to 20 with the addition of five new γ-transitions of energies 1240, 840, 626, 1178 and 846 keV above the 5538 keV state.…”

“…4. Parity for energy levels in bands B1, B2 and B3 are assigned based on earlier works and from systematics [15,25,28]. Details of the γ-ray energies, measured relative intensities, DCO ratios and multipolarities of the observed γ-ray transitions of 70 Ge are summarized in Table I.…”

Recoil-βtagging study of theN=Znucleus66As

“…Taking into account the isospin symmetry between isobaric multiplets, the closest transition in 66 As, energywise, to the 66 Ge 2 + 1 → 0 + 1 transition is the 963-keV transition [37]. The angular distribution information [A 2 = 0.30 (4)] and the value of the angular distribution ratio [R = 1.27 (15)] obtained for the 963-keV peak suggests a stretched E2 character.…”

“…The calculated CED with JUN45 interaction for the mass A = 66 pair is shown as dashed line to compare with the experimental data. Data are taken from Refs [6,37,[41][42][43]…”