Band crossings inTa166

Abstract

High-spin states in the odd-odd nucleus 166 Ta are investigated through the 5n channel of the 51 V + 120 Sn reaction. Four new bands are observed and linked into the previous level scheme. Configurations for the bands are proposed, based on measured alignments and B(M1)/B(E2) transition strength ratios.

High-spin study of162Ta

“…In accordance with the Gallagher-Moszkowski rule [26] we propose that the parallel coupling of the valence particle angular momenta lies lower in energy than the antiparallel coupling at the bandhead in this odd-odd nucleus (i.e., a likely scenario is that the 162 Ta yrast band is built on a configuration where a high-πh 11/2 proton is coupled with a low-νi 13/2 neutron with a resulting band head angular momentum and parity 9 − ). Similar yrast configurations have been observed in other neighboring odd-odd Z = 73 isotopes [1,5,27] and N = 89 158 Tm and 160 Lu isotones [28,29].…”

“…This was associated by Lagergren et al [3] with an alignment of a more weakly shape-polarizing pair of mixed-character f 7/2 , h 9/2 neutrons. A similar, but less pronounced effect is observed in 162 Ta while in the heavier odd-odd 166,168 Ta isotopes [5,27] the staggering pattern (i.e., the signature splitting is reversed after the band crossing). Hence, it appears that the change in the signature inversion pattern for N = 89 might be associated with the character of the S band, after the crossing.…”

“…One of the questions of interest in these structures is the energy splitting between the two signatures in strongly coupled bands built on high-j single-particle configurations and how it varies with angular momentum. For the Ta isotopes, significant signature splitting has been observed in the yrast rotational bands of both the odd-A [built on the πh 11/2 quasiparticle (qp) configuration] and even-A (built on the πh 11/2 ⊗ νi 13/2 qp configuration) isotopes [1][2][3][4][5] and is usually believed to be associated with triaxial shapes induced by the deformation-driving properties of the πh 11/2 and νi 13 the region is the signature inversion in the yrast band of some odd-odd A ≈ 160 nuclides [6][7][8][9]. This phenomenon has been studied using various theoretical approaches [10][11][12][13][14][15], and several attempts have been made to explain its origin.…”

First identification of rotational band structures inRe9175166

“…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].…”

Band crossings in 168Ta: A particle-number conserving analysis

“…Meanwhile, a considerable amount of data of the high-spin rotational bands in this mass region have been obtained in this process. Especially some doubly-odd nuclei, e.g., 166,168,170,172 Ta [11,12,13,14], 168,170,172,174,176 Re [15,16,17,18,19], etc., which are characterized by fairly small quadrupole deformations, provide a good opportunity to the understanding of the dependence of band crossing frequencies and angular momentum alignments on the occupation of specific single-particle orbitals.…”