Wobbling mode inTa167

Abstract

The collective wobbling mode, the strongest signature for the rotation of a triaxial nucleus, has previously been seen only in a few Lu isotopes in spite of extensive searches in nearby isotopes. A sequence of transitions in the N = 94 167 Ta nucleus exhibiting features similar to those attributed to the wobbling bands in the Lu nuclei has now been found. This band feeds into the πi 13/2 band at a relative energy similar to that seen in the established wobbling bands and its dynamic moment of inertia and alignment properties are nearly identical to the i 13/2 structure over a significant frequency range. Given these characteristics, it is likely that the wobbling mode has been observed for the first time in a nucleus other than Lu, making this collective motion a more general phenomenon. PACS number(s): 21.10. Re, 23.20.Lv, 27.70.+q Our understanding of the wobbling mode in nuclei (and the associated stable triaxial deformation) has evolved quickly over the past decade. Bohr and Mottelson [1] first proposed that the rotation of a stable triaxially deformed nucleus would result in the presence of wobbling excitations. These excitations occur because the rotational angular momentum is not aligned with any of the body-fixed axes; rather it precesses and wobbles around one of these axes in a manner similar to that of an asymmetric top.In 1995, Schnack-Petersen et al.[2] first suggested that rotational bands based on proton i 13/2 excitations in 163,165 Lu are associated with a triaxial strongly deformed (TSD) potential well. The large deformation is mainly due to the occupation of the intruder i 13/2 orbital, and the triaxial deformation (γ = 20 • ) results from an N = 94 shell gap that develops with enhanced quadrupole deformation ( 2 ≈ 0.37). No direct experimental evidence for triaxiality was observed until the wobbling mode was confirmed in 163 Lu by Ødegård et al.[3]. This seminal work established the existence of a band feeding into the πi 13/2 structure where the two sequences have nearly identical moments of inertia and alignments over a large frequency range. The similarities of the moments of * Present address: inertia and alignments are a predicted feature for a wobbling band as the intrinsic structure for both bands should be the same; the only difference between the two is the degree to which the rotational angular momentum vector lies off axis. The collective wobbling behavior can thus be described within a phonon model, where the energy of each band is equal to E =¯h 2 2J I (I + 1) +hω w (n w + 1/2), wherehω w = hω rot (J x − J y )(J x − J z )/(J y J z ) [1]. The n w = 0 phonon number is assigned to the energetically lowest band in the family, as its angular momentum vector lies closest to a body axis, and in the case of the Lu isotopes, this is associated with the πi 13/2 band. Wobbling excitations with n w = 1, 2, 3, etc. then follow, each lying successively higher in energy as the rotational angular momentum vector progressively lies farther from the body axis with increasing n w . Indeed, Jense...

Properties of triaxial, strongly deformed bands inTa167andLu167Sugawara-Tanabe1, Tanabe2 2010Phys. Rev. C232200View full textAdd to dashboardCite

“…(1) and (2). Generally, the experimental data for TSD bands [4][5][6][7][8][9] show some evolution with increasing I both in the excitation energy relative to a reference and the dynamical moment of inertia. These experimental results indicate there still remains the Coriolis antipairing (CAP) effect in the rotating core.…”

“…The purpose of the present communication is to apply the angular-momentum dependence of moments of inertia to both isobars 167 Ta and 167 Lu with a common set of parameters to describe the energy levels and the ratios of B(E2) out /B(E2) in observed by Hartley et al [9]. The model Hamiltonian is given by…”

“…Then the overlap becomes (9) with (Ô) ≡ 1/ a 0|0 α . In this expression, n a (= I − K) and n b (= j − ) stand for the eigenvalues ofn a andn b , respectively.…”

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

“…For nuclei depicting triaxial shapes, there is a long-standing issue whether these nuclei have rigid or soft γ-deformation (see, for example, discussions in Refs. [3][4][5]). Traditionally, there are two extreme phenomenological models that describe the triaxiality: the one with a rigid-γ deformation of Davydov and Flippov (DF) [6] and the γ-soft model of Wilets and Jean [7].…”

Identification of triaxial strongly deformed bands in164Hf

“…Cranking calculations based on the modified-oscillator model suggest that the bands are associated with four-quasiparticle configurations that involve high-j intruder (i 13 Considerable progress has been made over the past decade in the study of collective motion associated with a stable triaxial nuclear shape. In the A ∼ 160 mass region, families of rotational bands based on a wobbling excitation have been identified in 163,165,167 Lu [1][2][3][4], possibly in 161 71 Lu [5], and, more recently, in 167 73 Ta 94 [6]. Triaxial strongly deformed (TSD) bands based on quasiparticle excitations have also been observed in neighboring nuclei, such as 164 Lu [7] and 163 69 Tm 94 [8].…”