Reaching degeneracy in two-quasiparticle chiral bands

Lawrie, E. A.; Shirinda, O.

doi:10.1016/j.physletb.2010.04.047

Cited by 47 publications

(46 citation statements)

References 24 publications

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“…This can be understood since the mass parameters is proportional to ω 2 as seen in Eqs. (18)- (19). For the curvature K ϕ , it first exhibits a decrease behavior up to ω = 0.20 MeV, and then gradually increases with the increase of rotational frequency.…”

Section: A Collective Parametersmentioning

confidence: 95%

Two-dimensional collective Hamiltonian for chiral and wobbling modes

et al. 2016

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A two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor (γ = −30 • ) coupling to one h 11/2 proton particle and one h 11/2 neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree with the exact solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters.In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.

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Section: A Collective Parametersmentioning

confidence: 95%

Two-dimensional collective Hamiltonian for chiral and wobbling modes

et al. 2016

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“…A multiplet of two chiral systems, built on the same configuration of two valence nucleons, behaving as a particle and a hole in the same single shell, generates four bands arranged in two distinct pairs [1,21]. However, when the configuration is allowed to span a larger configuration space than a single orbital per nucleon, the partner bands in the pair show distinct differences [22,23], including increased relative fig. 4(e).…”

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confidence: 99%

DSAM lifetime measurements for the chiral pair in 194Tl

Masiteng

Pasternak

Lawrie³

et al. 2016

Eur. Phys. J. A

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Abstract. Most important for the identification of chiral symmetry in atomic nuclei is to establish a pair of bands that are near-degenerate in energy, but also in B(M 1) and B(E2) transition probabilities. Dedicated lifetime measurements were performed for four bands of 194 Tl, including the pair of four-quasiparticle chiral bands with close near-degeneracy, considered as a prime candidate for best chiral symmetry pair. The lifetime measurements confirm the excellent near-degeneracy in this pair and indicate that a third band may be involved in the chiral symmetry scenario.Chiral systems can exist in nuclei with triaxially deformed shape. Such nuclei rotate collectively predominantly around their intermediate axis. Should the valence nucleons have both particle and hole nature, their singleparticle angular momenta would align along the short and long nuclear axes, respectively. Then the total angular momentum of the nucleus will have large projections along the three major nuclear axes, forming a left-handed or a right-handed systems and exhibiting chiral symmetry.Nuclear chiral symmetry generates a pair of rotational bands with the same parity and with near-degenerate properties; for instance they have similar excitation energies, alignments, and reduced B(M 1) and B(E2) transition probabilities [1]. Most of the chiral bands known to date have been identified based on similarity in the excitation energy and alignments, but very often the most crucial chirality test (see ref.[2]), i.e. the similarity in the B(M 1) and B(E2) transition rates remain outstanding, because it needs dedicated lifetime measurements.The formation of more than one chiral system in the same nucleus is a very rare event. To date chiral multiplets were proposed in only two nuclei, Tl [5], including the only fourquasiparticle chiral pair known to date. This is also the only chiral pair for which chirality persists through a backbend. Furthermore, this chiral pair shows perhaps the best near-degeneracy found to date [6].The 181 Ta( 18 O, 5n) reaction was employed at a beam energy of 91 MeV. The target was a 1 mg/cm 2 181 Ta foil with a thick Bi layer evaporated on the back. The recoils were completely stopped in the Bi backing. The emitted γ-rays were detected with the AFRODITE array [7,8] at iThemba LABS, comprising 9 Compton-suppressed clover detectors, and 6 LEPS detectors. The trigger required 3 coincident γ-rays, with at least two detected in the clovers. Four clover detectors were arranged at 45• , another four were placed at 135• , while the remaining detectors were situated at 90• with respect to the beam direction. Data were sorted into two asymmetric matrices, with the γ-ray energies detected at 45• and at 135• , respectively, stored into one axis, while the coincident γ-ray energies registered at any angle were stored into the second axis. Gated, background-subtracted, forward (45 • ) and backward (135 • ) spectra were used to analyze the Doppler

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“…configuration of one proton and one neutron restricted to a configuration space of one orbital each, which in this case are the lowest-and the highest-energy orbitals of the high-j shells. The triaxiality parameter is fixed to J = 30 o for the 100 and 130 mass region [8] and J = 36 o for A = 190 mass region [9].…”

Section: Calculations and Resultsmentioning

confidence: 99%