Close near-degeneracy in a pair of four-quasiparticle bands in 194Tl

Masiteng, P. L.; Lawrie, E. A.; Ramashidzha, T. M.; Bark, R. A.; Carlsson, B. G.; Lawrie, J. J.; Lindsay, R.; Komati, F.; Kau, J.; Maine, P.; Maliage, S. M.; Matamba, I.; Mullins, S. M.; Murray, S.; Mutshena, K. P.; Pasternak, A. A.; Ragnarsson, I.; Roux, D. G.; Sharpey‐Schafer, J. F.; Shirinda, O.; Vymers, P.

doi:10.1016/j.physletb.2013.01.006

Cited by 46 publications

(42 citation statements)

References 17 publications

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“…The upper part (I 18) of Bands 1 and 4 were assigned a four-quasiparticle πh 9/2 ⊗ νi −3 13/2 configuration, which includes valence nucleons with both particle (πh 9/2 ) and hole (νi −3 13/2 ) nature. Furthermore triaxial shape was predicted for this configuration in 194 Tl [6]. Such features are characteristic for chiral symmetry systems.…”

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confidence: 55%

“…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].…”

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confidence: 75%

“…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.…”

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confidence: 99%

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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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confidence: 55%

“…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].…”

mentioning

confidence: 75%

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DSAM lifetime measurements for the chiral pair in 194Tl

Masiteng

Pasternak

Lawrie³

et al. 2016

Eur. Phys. J. A

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“…Such chiral doublet bands were first observed in N ¼ 75 isotones [2]. So far, more than 30 experimental candidates have been reported in the A ∼ 80, 100, 130, and 190 mass regions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].Based on constrained triaxial covariant density functional theory (CDFT) calculations, it has been suggested that multiple chiral doublet (MχD) bands can exist in a single nucleus [21][22][23][24][25][26]. The theoretical prediction of MχD bands stimulated lots of experimental efforts [27][28][29][30][31].…”

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confidence: 99%

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Evidence for Octupole Correlations in Multiple Chiral Doublet Bands

Liu¹,

Wang²,

Bark³

et al. 2016

Phys. Rev. Lett.

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106

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Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive-and negative-parity bands have been identified in 78 Br. They are interpreted as multiple chiral doublet bands with octupole correlations, which is supported by the microscopic multidimensionally-constrained covariant density functional theory and triaxial particle rotor model calculations. This observation reports the first example of chiral geometry in octupole soft nuclei. DOI: 10.1103/PhysRevLett.116.112501 Spontaneous symmetry breaking is a fundamental concept in nature. As a many-body quantum system, the atomic nucleus carries a wealth of information on fundamental symmetries and symmetry breaking. As one example, chiral symmetry breaking in atomic nuclei has attracted considerable attention and intensive discussion since it was first predicted by Frauendorf and Meng [1]. They pointed out that, in the intrinsic frame of the rotating triaxial nucleus, the total angular momentum vector may lie outside the three principal planes, referred to as chiral geometry. The spontaneous chiral symmetry breaking in the laboratory frame may give rise to pairs of nearly degenerate ΔI ¼ 1 bands with the same parity, i.e., chiral doublet bands. Such chiral doublet bands were first observed in N ¼ 75 isotones [2]. So far, more than 30 experimental candidates have been reported in the A ∼ 80, 100, 130, and 190 mass regions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].Based on constrained triaxial covariant density functional theory (CDFT) calculations, it has been suggested that multiple chiral doublet (MχD) bands can exist in a single nucleus [21][22][23][24][25][26]. The theoretical prediction of MχD bands stimulated lots of experimental efforts [27][28][29][30][31]. The first experimental evidence for MχD bands was reported in 133 Ce [27], which confirmed the manifestation of triaxial shape coexistence in this nucleus. Later, Kuti et al. reported a novel type of MχD bands with the same configuration in 103 Rh [29], which showed that chiral geometry can be robust against the increase of the intrinsic excitation energy.Compared to the A ∼ 130 and 100 mass regions, the A ∼ 80 mass region is a relatively new and less studied territory for the investigation of chiral symmetry breaking in rotating nuclei, with only one report of chiral doublet bands based on the πg 9=2 ⊗ νg 9=2 configuration in odd-odd 80 Br [18]. In 78 Br, the πg 9=2 ⊗ νg 9=2 band was suggested to have an obvious triaxial shape [32], which is suitable for the construction of chiral doublet bands.

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Excited Nuclear States for Tl-194 (Thallium)

Sukhoruchkin¹,

Soroko²

2016

Supplement to I/25 a-G

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Close near-degeneracy in a pair of four-quasiparticle bands in 194Tl

Cited by 46 publications

References 17 publications

DSAM lifetime measurements for the chiral pair in 194Tl

DSAM lifetime measurements for the chiral pair in 194Tl

Evidence for Octupole Correlations in Multiple Chiral Doublet Bands

Excited Nuclear States for Tl-194 (Thallium)

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