Multiple band structures in169,170Re: Search for the wobbling mode in169Re, and residual-interaction analysis of structures in

Abstract

Although the observation of wobbling was once thought to be possibly confined to lutetium isotopes in N ≈ 94 nuclei, the identification of this exotic collective mode in 167 Ta has raised the question of the role of the proton Fermi surface with regard to this phenomenon. In order to investigate this issue, an experiment was performed to populate high-spin states in the N = 94 nucleus 169 Re. The heavy-ion reaction 55 Mn + 118 Sn was used in conjunction with Gammasphere to detect the emitted γ rays. Over 130 new transitions were added to the 169 Re level scheme, including the first identification of the πi 13/2 rotational sequence in this nucleus. This configuration is the structure on which all known wobbling sequences are based, but no wobbling band was observed, likely due to the fact that the πi 13/2 sequence is located at a relatively high energy in comparison with the other structures found in 169 Re. Nine decay sequences are now established in this nucleus and are described within the context of the cranked shell model. In addition, significant extension of the level scheme of the odd-odd 170 Re nucleus was possible and a discussion of the residual interactions for the πh 9/2 νi 13/2 and πi 13/2 νi 13/2 configurations in this region is given as well.

First identification of rotational band structures inRe9175166

“…With the β 2 deformation around 0.17 predicted by our TRS calculations, the Nilsson orbitals near the Fermi surface emanate from the h 11/2 and d 5/2 subshells for protons and are of i 13/2 , h 9/2 , and f 7/2 characters 166 Re. Such an yrast configuration has also been assigned for 170,172 Re [8,9] and 164 Ta [6].…”

“…6(b), i.e., somewhat later than the predicted BC crossing. The BC crossing has been observed in the yrast rotational bands of 170,172 Re [8,9], 162 Lu [35], and 162,164,166 Ta [5][6][7].…”

“…For example, the first i 13/2 (AB) rotational alignment is responsible for the backbending in 164,166 W [2,3] and 163 Ta [4] and their heavier isotopes. This crossing is blocked in nearby odd-N tantalum, tungsten, and rhenium nuclei, but the next available i 13/2 crossing is an important feature in their collective structures, such as the second i 13/2 (BC) alignment in 165 W [3], 162,164,166 Ta [5][6][7], and 170,172 Re [8,9]. The occupation of the proton h 11/2 and neutron i 13/2 intruder orbitals near the Fermi level may also lead to shape polarization effects, particularly in the γ degree of freedom, owing to the spatial orientation of these orbitals [10].…”

Possible deformation evolution in theπi13/2structure of171Re

“…However, as seen in other nearby nuclei [30][31][32], it is likely that band 6 exchanges character and becomes the πh 11/2 νAE configuration instead. Indeed, this sequence was recently identified in 169 Re [33]. With this interpretation, the BC crossing is allowed.…”

High-spin structure of odd-oddRe172

“…In addition, Ref. [2] discusses the results of 170 Re and the influence of residual interactions in this region. The present work focuses on the nearby isotope 172 Re, where the level scheme was significantly extended.…”