Mixing of quasiparticle excitations andγvibrations in transitional nuclei

Abstract

Evidence of strong coupling of quasiparticle excitations with γ-vibration is shown to occur in transitional nuclei. High-spin band structures in 166,168,170,172 Er are studied by employing the recently developed multiquasiparticle triaxial projected shell model approach. It is demonstrated that a low-lying K = 3 band observed in these nuclei, the nature of which has remained unresolved, originates from the angular-momentum projection of triaxially deformed two-quasiparticle (qp) configurations. Further, it is predicted that the structure of this band depends critically on the shell filling: in 166 Er the lowest K = 3 2-qp band is formed from proton configuration, in 168 Er the K = 3 neutron and proton 2-qp bands are almost degenerate, and for 170 Er and 172 Er the neutron K = 3 2-qp band becomes favored and can cross the γ-vibrational band at high rotational frequencies. We consider that these are few examples in even-even nuclei, where the three basic modes of rotational, vibrational, and quasi-particle excitations co-exist close to the yrast line.

Mixing effects onK-forbidden transition rates from the 6+isomers in theN= 104 isotones

“…Recently, the triaxial projected shell model (TPSM) that includes various multi-qp configurations became available [5,19,20,21]. In the following, we take advantage of this development.…”

“…For example, evidence was shown [5] for strong coupling of quasiparticle (qp) excitations with the γ vibration in rare-earth transitional nuclei, and this was used to explain the systematic behavior of the low-lying K π = 3 + 2-qp band. With a quantitative reproduction of the experimental data, that study showed clearly, as expected, that the band mixing depended sensitively on the proximity of the members of the γ vibrational band to those of the 3 + 2-qp band.…”

Nature ofγdeformation in Ge and Se nuclei and the triaxial projected shell model description

“…The model has recently been extended [13-17, 19, 20] to include multi-qp configurations in the model space, which allows one to describe states of collective γ-vibrations and qp excitations on an equal footing. For instance, the multi-qp TPSM approach has been used to investigate the interplay between the vibrational and the quasiparticle excitation modes in 166−172 Er [15]. It was demonstrated that a low-lying K = 3 bands observed in these nuclei, the nature of which had remained unresolved, are built on triaxially-deformed 2-qp states.…”

“…In the next section, we provide a few details of the TPSM model for completeness and further details can be found in our earlier publications [13][14][15][16][17][18]. Section III is completely devoted to the investigation of 76 Ge and in section IV, the results of the neighboring Ge-and Se-isotopes are presented and discussed.…”

Triaxial projected shell model study of the rapid changes inB(E2)for180−190Pt isotopes

“…This approach opens up opportunities to treat problems that otherwise are difficult to interpret in the axial-symmetry limit. For example, TPSM approach has more recently been used to investigate the interplay between the vibrational and the quasi-particle excitation modes in 166−172 Er [32]. It has been established that a low-lying K = 3 bands observed in these nuclei are, in fact, built on triaxially-deformed two-quasiparticle states.…”