Tilted axis rotation, candidates for chiral bands, and wobbling motion in138Nd

Abstract

High-spin states in138 Nd were investigated using the reaction 94 Zr( 48 Ca,4n), detecting coincident γ-rays with the gasp spectrometer. A rich level scheme was constructed including 4 bands of negative parity at low spins, 8 bands of dipole transitions and 8 bands of quadrupole transitions at medium spins. The Cranked Shell Model and the Tilted Axis Cranking model are used to assign configurations to the observed bands, where zero pairing is assumed. For selected configurations the case of finite pairing is also considered. A consistent notation for configuration assignment is introduced, which applies both for zero and finite pairing. The observed bands are interpreted as rotation around the short and long principal axes (quadrupole bands), as well as around a tilted axis (dipole bands). The dipole bands have an intermediate character, between magnetic and collective electric rotation. A pair of dipole bands are candidates for chiral partners, the first case this property has been identified in an even-even nucleus. The possible existence of the wobbling mode at low deformation and medium spins is discussed. The consistent interpretation of the multitude of observed bands strongly supports the existence of stable triaxial deformation at medium spins in 138 Nd.

Multiple triaxial bands inNd138

“…The high-spin bands reported in the present paper are discussed within the framework of the cranked Nilsson-Strutinsky (CNS) model and represent a nice confirmation of the theoretical calculations which predict that at high spins, the dominant configurations in 138 Nd are based on triaxial shapes, stabilized over extended spin ranges. Together with the high-spin triaxial bands already reported in 139 Nd [17] and 140 Nd [24], and those in 141 Nd that will be published soon [25], the newly observed bands in 138 Nd contribute to the completion of the largest set of high-spin bands observed in a restricted range of nuclei, giving thus confidence in the CNS predictions of stable triaxiality at high spins in the region of Nd nuclei with few holes in the N = 82 shell closure.…”

“…The total number of bands identified in 138 Nd, including the 21 bands at low and medium spins reported recently in Ref. [24], the highly deformed bands reported in Ref. [22] and the present 14 bands at high spins, amounts to 36.…”

“…The level scheme of 138 Nd is therefore one of the better known from low to very high spins. The bands at low and medium spins have been interpreted within the framework of the tilted axis cranking (TAC) model, but random phase approximation calculations have also been performed to understand certain band structures [24]. The overall consistent description of all observed bands as configurations based on a triaxial nuclear shape strongly suggests the existence of a stable triaxial deformation at medium spin in this mass region.…”

Spectroscopy of135La

“…The nuclei around the N = 82 shell closure offer a unique laboratory for the study of the shape coexistence in different spin regions, from low and medium spins where spherical and triaxial shapes compete [1,2]. These nuclei often present isomeric states which have simple multi-quasiparticle configurations and are therefore easier to interpret.…”

Triaxiality and exotic rotations at high spins inCe134

“…A further motivation of this work is to study the evolution of triaxiality in Ce nuclei, with the aim of verifying the extent to which the conclusions drawn from the study of Nd sequences [12][13][14][15][16][17] are applicable to similar bands of neighboring nuclei. Unfortunately, it has not hitherto been possible to draw any definite conclusions on the structure of the triaxial bands in 133,134 Ce [7,18] as none of the observed structures were linked to low-lying states.…”