Browsing by Author "Ndayishimye, J."

Now showing 1 - 7 of 7
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    Chiral 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.
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    Competition 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.
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    First candidates for γ vibrational bands built on the [505]11/2– neutron orbital in odd-A Dy isotopes
    (American Physical Society, 2020-05-10) Majola, S. N. T.; Sithole, M. A.; Mdletshe, L.; Hartley, D.; Timar, J.; Nyako, B. M.; Allmond, J. M.; Bark, R. A.; Beausang, C.; Bianco, L.; Bucher, T. D.; Bvumbi, S. P.; Carpenter, M.P.; Chiara, C. J.; Cooper, N.; Cullen, D. M.; Curien, D.; Dinoko, T. S.; Gall, B. J. P.; Garrett, P. E.; Greenlees, P. T.; Hirvonen, J; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Ketelhut, S.; Kheswa, B. V.; Kondev, F.G.; Korichi, A.; Kulp, W.D.; Lauritsen, T.; Lawrie, E. A.; Makhathini, L.; Masiteng, P. L.; Maqabuka, B.; McCutchan, E.A.; Miller, D.; Miller, S.; Minkova, A.; Msebi, L.; Mthembu, S. H.; Ndayishimye, J.; Nieminen, P.; Ngcobo, P. Z.; Ntshangase, S. S.; Orce, J. N.; Peura, P.; Rahkila, P.; Redon, N.; Riedinger, L. L.; Riley, M. A.; Roux, D. G.; Ruotsalainen, P.; Piot, J.; Saren, J.; Sharpey-Schafer, J. F.; Scholey, C.; Shirinda, O.; Simpson, J.; Sorri, J.; Stefanescu, I.; Stolze, S.; Uusitalo, J.; Wang, X.; Werner, V.; Wood, J.L; Yu, C-H.; Zhu, S.; Zimba, G.
    Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the 155Gd(α,2n)157Dy and 148Nd(12C, 5n)155Dy reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a Kπ= 2+ γ vibrational band, built on the [505]11/2– neutron orbital, in both odd-A 155, 157Dy isotopes. The coupling of the first excited K=0+ states or the so-called β vibrational bands at 661 and 676 keV in 154Dy and 156Dy to the [505]11/2– orbital, to produce a Kπ=11/2- band, was not observed in both 155Dy and 157Dy, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei 154Dy and 156Dy are also discussed.
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    Near-degenerate rotational bands in the Tl isotopes
    (Jagellonian University, 2018) Lawrie, E. A.; Ndayishimye, J.; Masiteng, P. L.; Shirinda, O.
    Sets of near-degenerate rotational bands built on configurations involving nh9/2 particle and vi13/2 holes were observed in the neighbouring 193;194Tl isotopes. Such sets of bands, involving particle and hole configurations and occurring in nuclei with triaxial shape, are caused by chiral symmetry formed in angular momentum space. Each nuclear chiral system is expected to generate a pair of near-degenerate partner bands. However, several sets of three partner bands were observed in these Tl isotopes, raising questions whether one or two chiral systems are formed, and which two bands are partners in the chiral pair. Many-particle-rotor model calculations reproduce well the features of the observed negative-parity bands in 193;194Tl and support the suggested chiral geometry of the angular momenta.
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    New 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.
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    Spectroscopy of low-spin states in 157Dy : Search for evidence of enhanced octupole correlations
    (American Physical Society, 2019) Majola, S. N. T.; Bark, R. A.; Bianco, L.; Bucher, T. D.; Bvumbi, S. P.; Cullen, D. M.; Garrett, P. E.; Greenlees, P. T.; Hartley, D.; Hirvonen, J.; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Ketelhut, S.; Kheswa, B. V.; Korichi, A.; Lawrie, E. A.; Masiteng, P. L.; Maqabuka, B.; Mdletshe, L.; Minkova, A.; Ndayishimye, J.; Nieminen, P.; Nyako, B. M.; Peura, P.; Rahkila, P.; Riedinger, L. L.; Riley, M.; Roux, D.; Ruotsalainen, P.; Saren, J.; Sharpey-Schafer, J. F.; Scholey, C.; Shirinda, O.; Sithole, A.; Sorri, J.; Stolze, S.; Timar, J.; Uusitalo, J.; Zimba, G.
    Low-spin states of ¹⁵⁷Dy have been studied using the JUROGAM II array, following the ¹⁵⁵Gd (α, 2n) reaction at a beam energy of 25 MeV. The level scheme of ¹⁵⁷Dy has been expanded with four new bands. Rotational structures built on the [523]5/2⁻ and [402]3/2⁺ neutron orbitals constitute new additions to the level scheme as do many of the inter- and intraband transitions. This manuscript also reports the observation of cross I⁺ →(I–1) ⁻ and I⁻ →(I–1)⁺ E1 dipole transitions interlinking structures built on the [523]5/2⁻ (band 5) and [402]3/2⁺ (band 7) neutron orbitals. These interlacing band structures are interpreted as the bands of parity doublets with simplex quantum number s=–i related to possible octupole correlations.
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    β 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.