Browsing by Author "Lawrie, E. A."

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    Chirality and octupole correlations in As-74
    (Physical Review C, 2022) Xiao, X.; Lawrie, E. A.; Wang, S. Y.
    High-spin states in 74As were studied using the 74Ge(4He, 1p3n) reaction at beam energies of 58.6 and 62.6 MeV. Two positive- and one negative-parity bands have been identified in 74As. The two positive-parity bands are interpreted as chiral doublet bands, which is supported by the triaxial particle rotor model. Three electric dipole transitions linking the yrast positive- and negative-parity bands were also observed in this work, suggesting the existence of octupole correlations in 74As.
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    Collective rotational bands at low excitation energy in 186Os: Vibrational and rotational degrees of freedom
    (American Physical Society, 2022) Mdletshe, Linda; Yang, X. Q.; Lawrie, E. A.
    Collective structures in 186Os have been investigated through the 186W(4He, 4n) 186Os reaction, at a beam energy of 48 MeV. The low-lying bands built on the excited 0+ 2 , 2+ 2 , and 4+ 3 states have been extended up to spins of 12+, 15+, and 8+, respectively, and a number of new linking transitions were identified. The features of the collective bands in 186Os, such as level energies, are presented in the context of a systematic study of the neighboring even-even 182–192Os isotopes. In addition, the validity of the K-selection rule, stemming from a description based on axial symmetry of the nuclear shape, is examined. The observed decays between the rotational bands support a description where K is conserved. However, some K-forbidden decays were also identified, suggesting that a model allowing for small K admixtures is probably required. The experimental data are further compared with calculations using a five-dimensional collective Hamiltonian based on covariant density functional theory. The calculations predict that the collective bands are associated with different nuclear shapes, varying in quadrupole deformation, triaxiality, and softness.
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    Gamma spectroscopy and lifetime measurements in the doubly-odd 194tl nucleus, revealing possible chiral symmetry breaking
    (University of the Western Cape, 2013) Masiteng, Paulus Lukisi; Lawrie, E. A.; Lindsay, R.
    In the first experiment high spin states in 194Tl, excited through the 181Ta (18O, 5n) heavyion fusion evaporation reaction were studied using the AFRODITE array at iThemba LABS. The γ-γ coincidences, RAD ratios and linear polarization measurements were carried out and the previously known level scheme of 194Tl was significantly extended. A total of five rotational bands four of which are new were observed. A pair of rotational bands associated with the πh9/2 ⊗ νi−1 13/2 configuration at lower spins and with the πh9/2 ⊗ νi−3 13/2 configuration at higher spins was found and interpreted as the first possible chiral bands followed above the band crossing. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. In the second experiment lifetimes in 194Tl were measured using the DSAM technique with the excited states in this nucleus populated through the 181Ta (18O, 5n) reaction. A total of 25 lifetimes and 30 reduced transition probabilities of magnetic dipole B(M1) and electric quadrupole B(E2) have been evaluated. Furthermore B(M1) and B(E2) reduced transition probabilities in Bands 1 and 4, which have been regarded as chiral candidates, were found to be close to each other and reveals strong splitting along spin values. This further supports the proposed chiral nature of these two bands.
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    Studying chirality in a ~ 100, 130 and 190 mass regions
    (University of the Western Cape, 2011) Shirinda, Obed; Lawrie, E. A.; Lindsay, R.; Dept. of Physics; Faculty of Science
    Chirality is a nuclear symmetry which is suggested to occur in nuclei when the total angular momentum of the system has an aplanar orientation [Fra97, Fra01]. It can occur for nuclei with triaxial shape, which have valence protons and neutrons with predominantly particle and hole nature. It is expected that the angular momenta of an odd particle and an odd hole (both occupying high-j orbitals) are aligned predominantly along the short and the long axes of the nucleus respectively, whereas the collective rotation occurs predominantly around the intermediate axis of a triaxially deformed nucleus in order to minimize the total energy of the system. Such symmetry is expected to be exhibited by a pair of degenerate DI = 1 rotational bands, i.e. all properties of the partner bands should be identical. The results suggested that spin independence of the energy staggering parameter S(I ) within two-quasiparticle chiral bands (previously suggested a fingerprint of chirality) is found only if the Coriolis interaction can be completely neglected. However, if the configuration is nonrestricted, the Coriolis interaction is often strong enough to create considerable energy staggering. It was also found that staggering in the intra- and inter-band B(M1) reduced transition probabilities (proposed as another fingerprint of chirality) may be a result of effects other than strongly broken chirality. Therefore, the use of the B(M1) staggering as a fingerprint of strongly broken chiral symmetry seems rather risky, in particular if the phase of the staggering is not checked.