Browsing by Author "Lawrie, J. J."
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- ItemAngular correlation measurement with the iThemba LABS segmented clover detector(Jagellonian University, 2019) Shirinda, O.; Lawriea, E. A.; Buchera, T. D.; Mthembua, S. H.; Dinoko, T. R. S.; Easton, J. L.; Mtshali, W. X.; Noncolela, S. P.; Duprez, D.; Lawrie, J. J.Measurements of the angular correlation function W(θ) were performed with the iThemba LABS segmented clover detector. A set of measurements with radioactive sources and irradiated targets was carried out to check the performance of the detector. At short detector-to-source distance, the detector covers the whole range of angles needed for precise angular correlation measurements. Preliminary results show that our detector can measure precisely angular correlation functions, including for transitions with large multipole order such as E3, M4, E4, etc., and deliver mixing ratios δ of mixed magnetic and electric nature.
- ItemChiral bands in 193Tl(Jagiellonian University, 2017-03) Ndayishimye, J.; Lawrie, E. A.; Shirinda, O.; Easton, J. L.; Wyngaardt, S. M.; Bark, R. A.; Bvumbi, S. P.; Dinoko, T. R. S.; Jones, P.; Kheswa, N. Y.; Lawrie, J. J.; Majola, S. N. T.; Masiteng, P. L.; Negi, D.; Orce, J. N.; Papka, P.; Sharpey-Schafer, J. F.; Stankiewicz, M.; Wiedeking, M.Since the introduction of chirality in nuclei, the search for chiral candidates in different mass regions has been a hot topic for about two decades. At iThemba LABS, a new chiral symmetry region, the thallium isotopes with mass A ≥ 90 was found. Candidate chiral bands were suggested in 198Tl and then in 194Tl. Most importantly, a comparison of the properties in the chiral partner bands in 194Tl showed that this nucleus is one of the best chiral candidates to date. A search for chiral symmetry in the neighboring thallium isotopes was undertaken. The results from a y-ray spectroscopy study in 193Tl performed at iThemba LABS, South Africa, are discussed.
- ItemCompetition of rotation around the intermediate and long axes in 193Tl(American Physical Society, 2019) Ndayishimye, J.; Lawrie, E. A.; Shirinda, O.; Easton, J. L.; Lawrie, J. J.; Wyngaardt, S. M.; Bark, R. A.; Bucher, T. D.; Bvumbi, S. P.; Dinoko, T. R. S.; Jones, P.; Kheswa, N. Y.; Majola, S. N. T.; Masiteng, P. L.; Negi, D.; Orce, J. N.; Sharpey-Schafer, J. F.; Wiedeking, M.High-spin states in ¹⁹³Tl were studied and the level scheme was revised and extended including the observation of new rotational bands. A surprising competition between bands built on the same πh9/2⊗νi13/2⁻² nucleon configurations is observed. It is suggested that it is generated by two different rotational modes of this triaxial nucleus: (i) a rotation around the intermediate nuclear axis, producing a pair of chiral symmetry bands, and (ii) a rotation around the long nuclear axis, producing a third band with lower alignment.
- ItemEvolution from quasivibrational to quasirotational structure in 155Tm and yrast 27/2− to 25/2− energy anomaly in the A ≈ 150 mass region(American Physical Society, 2019) Liu, L.; Wang, S. Y.; Wang, S.; Hua, H.; Zhang, S. Q.; Meng, Jie; Bark, R. A.; Wyngaardt, S. M.; Qi, B.; Sun, D. P.; Liu, C.; Li, Z. Q.; Jia, H.; Li, X. Q.; Xu, C.; Li, Z. H.; Sun, J. J.; Zhu, L. H.; Jones, P.; Lawrie, E. A.; Lawrie, J. J.; Wiedeking, M.; Bucher, T. D.; Dinoko, T.; Makhathini, L.; Majola, S. N. T.; Noncolela, S. P.; Shirinda, O.; Gal, J.; Kalinka, G.; Molnar, J.; Nyako, B. M.; Timar, J.; Juhasz, K.; Arogunjo, M.Excited states in 155Tm have been populated via the reaction 144Sm(16O, p4n)155Tm at a beam energy of 118 MeV. The ground-state band has been extended and a new side band of the ground-state band is identified. E-GOS curves and potential energy surface calculations are employed to discuss the structure evolution of the ground-state band. The newly observed side band in 155Tm is discussed based on the spin/energy systematics. In particular, the phenomenon of seniority inversion is proposed in 155Tm, and a systematic study of this phenomenon in the A ≈ 150 mass region is performed.
- ItemNew candidate chiral nucleus in the A ≈ 80 mass region : 82 35 Br 47(American Physical Society, 2019-11-07) Liu, C.; Wang, S. Y.; Qi, B.; Wang, S.; Sun, D. P.; Li, Z. Q.; Bark, R. A.; Jones, P.; Lawrie, J. J.; Masebi, L.; Wiedeking, M.; Meng, J.; Zhang, S. Q.; Hua, H.; Li, X. Q.; Li, C. G.; Han, R.; Wyngaardt, S. M.; Sun, B. H.; Zhu, L. H.; Bucher, T. D.; Kheswa, B. V.; Malatji, K. L.; Ndayishimye, J.; Shirinda, O.; Dinoko, T.; Khumalo, N.; Lawrie, E. A.; Ntshangase, S. S.A pair of nearly degenerate positive-parity bands were observed in 82 Br for the first time using the 82 Se(α,p3n) reaction. The positive-parity doublet bands are proposed to be chiral doublet bands based on the triaxial particle rotor model and the potential energy surface calculations. The root-mean-square values of the angular momentum components and their probability distributions are discussed in detail to exhibit the chiral geometry and its evolution in 82 Br.
- ItemProportional crosstalk for the iThemba LABS clover detector(Jagiellonian University, 2017-03) Noncolela, S. P.; Bucher, T. D.; Lawrie, E. A.; Dinoko, T. R. S.; Easton, J. L.; Erasmus, N.; Lawrie, J. J.; Mthembu, S. H.; Mtshali, W. X.; Shirinda, O.; Orce, J. N.Measurements of the proportional crosstalk were performed for the iThemba LABS segmented clover detector. More than 1000 crosstalk parameters were determined and a crosstalk correction algorithm was implemented successfully.
- ItemRotational structures in 196Hg(American Physical Society, 2019) Lawrie, J. J.; Lawrie, E. A.; Msezane, B.; Benatar, M.; Fedderke, M.; Mabala, G. K.; Mukherjee, S.; Mullins, S. M.; Mutshena, K. P.; Ncapayi, N. J.; Newman, R. T.; Sharpey-Schafer, J. F.; Smit, F. D.; Vymers, P.High spin states in ¹⁹⁶Hg were populated in the ¹⁹⁸Pt(α,6n) reaction at 65 MeV and γ−γ coincidence measurements were performed using the AFRODITE array at iThemba LABS. The level scheme was extended and new rotational bands were observed. A new dipole band was found. The previously reported dipole band was linked to other known states. Excitation energies, spins, and parities of all bands were determined. The bands were assigned nucleon configurations based on cranked shell model calculations.
- ItemSpectroscopic study of the possibly triaxial transitional nucleus 75Ge(American Physical Society, 2018) Niu, C. Y.; Dai, A. C.; Xu, C.; Hua, H.; Zhang, S. Q.; Wang, S. Y.; Bark, R. A.; Meng, Jie; Wang, C. G.; Wu, X. G.; Li, X. Q.; Li, Z. H.; Wyngaardt, S. M.; Zang, H. L.; Chen, Z. Q.; Wu, H. Y.; Xu, F. R.; Ye, Y. L.; Jiang, D. X.; Han, R.; Li, C. G.; Chen, X. C.; Liu, Q.; Feng, J.; Yang, B.; Li, Z. H.; Wang, S.; Sun, D. P.; Liu, C.; Li, Z. Q.; Zhang, N. B.; Guo, R. J.; Li, G. S.; He, C. Y.; Zheng, Y.; Li, C. B.; Chen, Q. M.; Zhong, J.; Zhou, W. K.; Zhu, B. J.; Deng, L. T.; Liu, M. L.; Wang, J. G.; Jones, P.; Lawrie, E. A.; Lawrie, J. J.; Sharpey-Schafer, J. F.; Wiedeking, M.; Majola, S. N. T.; Bucher, T. D.; Dinoko, T.; Magabuka, B.; Makhathini, L.; Mdletshe, L.; Khumalo, N. A.; Shirinda, O.; Sowazi, K.The collective structures of 75Ge have been studied for the first time via the 74Ge(α,2p1n) 75Ge fusionevaporation reaction. Two negative-parity bands and one tentative positive-parity band built on the νp1/2, νf5/2, and νg9/2 states, respectively, are established and comparedwith the structures in the neighboringN = 43 isotones. According to the configuration-constrained potential-energy surface calculations, a shape transition from oblate to prolate along the isotopic chain in odd-A Ge isotopes is suggested to occur at 75Ge. The properties of the bands in 75Ge are analyzed in comparison with the triaxial particle rotor model calculations.
- Itemβ and γ bands in N = 88 , 90, and 92 isotones investigated with a five-dimensional collective Hamiltonian based on covariant density functional theory : vibrations, shape coexistence, and superdeformation(American Physical Society, 2019-06-05) Majola, S. N. T.; Shi, Z.; Song, B. Y.; Li, Z. P.; Zhang, S. Q.; Bark, R. A.; Sharpey-Schafer, J. F.; Aschman, D. G.; Bvumbi, S. P.; Bucher, T. D.; Cullen, D. M.; Dinoko, T. S.; Easton, J. E.; Erasmus, N.; Greenlees, P. T.; Hartley, D. J.; Hirvonen, J.; Korichi, A.; Jakobsson, U.; Jones, P.; Jongile, S.; Julin, R.; Juutinen, S.; Ketelhut, S.; Kheswa, B. V.; Khumalo, N. A.; Lawrie, E. A.; Lawrie, J. J.; Lindsay, R.; Madiba, T. E.; Makhathini, L.; Maliage, S. M.; Maqabuka, B.; Malatji, K. L.; Masiteng, P. L.; Mashita, P. I.; Mdletshe, L.; Minkova, A.; Msebi, L.; Mullins, S. M.; Ndayishimye, J.; Negi, D.; Netshiya, A.; Newman, R.; Ntshangase, S. S.; Ntshodu, R.; Msebi, L.; Mullins, S. M.; Ndayishimye, J.; Negi, D.; Netshiya, A.; Newman, R.; Ntshangase, S. S.; Ntshodu, R.; Nyako, B. M.; Papka, P.; Peura, P.; Rahkila, P.; Riedinger, L. L.; Riley, M. A.; Roux, D. G.; Ruotsalainen, P.; Saren, J. J.; Scholey, C.; Shirinda, O.; Sithole, M. A.; Sorri, J.; Stankiewicz, M.; Stolze, S.; Timar, J.; Uusitalo, J.; Vymers, P. A.; Wiedeking, M.; Zimba, G. L.A comprehensive systematic study is made for the collective β and γ bands in even-even isotopes with neutron numbers N = 88 to 92 and proton numbers Z = 62 (Sm) to 70 (Yb). Data, including excitation energies, B(E0) and B(E2) values, and branching ratios from previously published experiments are collated with new data presented for the first time in this study. The experimental data are compared to calculations using a five-dimensional collective Hamiltonian (5DCH) based on the covariant density functional theory (CDFT). A realistic potential in the quadrupole shape parameters V (β,γ ) is determined from potential energy surfaces (PES) calculated using the CDFT. The parameters of the 5DCH are fixed and contained within the CDFT. Overall, a satisfactory agreement is found between the data and the calculations. In line with the energy staggering S(I) of the levels in the 2γ + bands, the potential energy surfaces of the CDFT calculations indicate γ -soft shapes in the N = 88 nuclides, which become γ rigid for N = 90 and N = 92. The nature of the 02 + bands changes with atomic number. In the isotopes of Sm to Dy, they can be understood as β vibrations, but in the Er and Yb isotopes the 02 + bands have wave functions with large components in a triaxial superdeformed minimum. In the vicinity of 152Sm, the present calculations predict a soft potential in the β direction but do not find two coexisting minima. This is reminiscent of 152Sm exhibiting an X(5) behavior. The model also predicts that the 03 + bands are of two-phonon nature, having an energy twice that of the 02 + band. This is in contradiction with the data and implies that other excitation modes must be invoked to explain their origin.