Browsing by Author "Malatji, K. L."

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    ¹³⁷,¹³⁸,¹³⁹La(n,γ) cross sections constrained with statistical decay properties of ¹³⁸,¹³⁹,¹⁴⁰La nuclei
    (American Physical Society, 2017) Kheswa, B. V.; Wiedeking, M.; Brown, J. A.; Larsen, A. C.; Goriely, S.; Guttormsen, M.; Garrote, F. L. Bello; Bernstein, L. A.; Bleuel, D. L.; Eriksen, T. K.; Giacoppo, F.; Gorgen, A.; Goldblum, B. L.; Hagen, T. W.; Koehler, P. E.; Klintefjord, M.; Malatji, K. L.; Midtbo, J. E.; Nyhus, H. T.; Papka, P.; Renstrm, T.; Rose, S. J.; Sahin, E.; Siem, S.; Tornyi, T. G.
    The nuclear level densities and γ-ray strength functions of ¹³⁸,¹³⁹,¹⁴⁰La were measured using the ¹³⁹La(³He,α), ¹³⁹La(³He,'³He), and ¹³⁹La(d,p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A∼140 region is discussed. The ¹³⁷,¹³⁸,¹³⁹La(n,γ) cross sections were calculated at s- and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. Good agreement is found between ¹³⁹La(n,γ) calculated cross sections and previous measurements.
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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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    Nuclear level densities and γ-ray strength functions of 180,181,182Ta
    (American Physical Society, 2019) Brits, C. P.; Malatji, K. L.; Wiedeking, M.; Kheswa, B. V.; Goriely, S.; Garrote, F. L. Bello; Bleuel, D. L.; Giacoppo, F.; Gorgen, A.; Guttormsen, M.; Hadynska-Klek, K.; Hagen, T. W.; Hilaire, S.; Ingeberg, V. W.; Klintefjord, H. Jia M.; Larsen, A. C.; Majola, S. N. T.; Papka, P.; Peru, S.; Qi, B.; Renstrom, T.; Rose, S. J.; Sahin, E.; Siem, S.; Tveten, G. M.; Zeiser, F.
    Particle-γ coincidence experiments were performed at the Oslo Cyclotron Laboratory with the ¹⁸¹Ta(d,X) and ¹⁸¹Ta(³He,X) reactions to measure the nuclear level densities (NLDs) and γ-ray strength functions (γSFs) of ¹⁸⁰,¹⁸¹,¹⁸²Ta using the Oslo method. The back-shifted Fermi-gas, constant temperature plus Fermi gas, and Hartree-Fock-Bogoliubov plus combinatorial models were used for the absolute normalizations of the experimental NLDs at the neutron separation energies. The NLDs and γSFs are used to calculate the corresponding ¹⁸¹Ta(n,γ) cross sections and these are compared to results from other techniques. The energy region of the scissors resonance strength is investigated and from the data and comparison to prior work it is concluded that the scissors strength splits into two distinct parts. This splitting may allow for the determination of triaxiality and a γ deformation of 14.9˚±1.8˚ was determined for ¹⁸¹Ta.
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    Re-estimation of 180Ta nucleosynthesis in light of newly constrained reaction rates
    (Elsevier, 2019-03-12) Malatji, K. L.; Wiedeking, M.; Goriely, S.; Brits, C. P.; Kheswa, B. V.; Bello Garrote, F. L.; Bleuel, D. L.; Giacoppo, F.; Gorgen, A.; Guttormsen, M.; Hadynska-Klek, K.; Hagen, T. W.; Ingeberg, V. W.; Klintefjord, M.; Larsen, A. C.; Papka, P.; Renstrom, T.; Sahin, E.; Siem, S.; Siess, L.; Tveten, G. M.; Zeiser, F.
    Recent measurements of the nuclear level densities and γ-ray strength functions below the neutron thresholds in 180,181,182Ta are used as input in the nuclear reaction code TALYS. These experimental average quantities are utilized in the calculations of the 179,180,181Ta radiative neutron capture cross sections. From the latter, astrophysical Maxwellian-averaged (n, γ) cross sections (MACS) and reaction rates are extracted, which in turn are used in large astrophysical network calculations to probe the production mechanism of 180Ta. These calculations are performed for two scenarios, the s-process production of 180,181Ta in Asymptotic Giant Branch (AGB) stars and the p-process nucleosynthesis of 180Tamin Type-II supernovae. Based on the results from this work, the s-process in stellar evolution is considered negligible in the production of 180Tamwhereas 181Ta is partially produced by AGB stars. The new measurements strongly constrain the production and destruction rates of 180Tamat p-process temperatures and confirm significant production of nature’s rarest stable isotope 180Tamby the p-process.
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    “Stapler” mechanism for a dipole band in 79Se
    (American Physical Society, 2019-10-24) Li, C. G.; Chen, Q. B.; Zhang, S. Q.; Xu, C.; Hua, H.; Wang, S. Y.; Bark, R. A.; Wyngaardt, S. M.; Shi, Z.; Dai, A. C.; Wang, C. G.; Li, X. Q.; Li, Z. H.; Meng, J.; Xu, F. R.; Ye, Y. L.; Jiang, D. X.; Han, R.; Niu, C. Y.; Chen, Z. Q.; Wu, H. Y.; Wang, X.; Luo, D. W.; Wu, C. G.; Wang, S.; Sun, D. P.; Liu, C.; Li, Z. Q.; Sun, B. H.; Jones, P.; Msebi, L.; Sharpey-Schafer, J. F.; Dinoko, T.; Lawrie, E. A.; Ntshangase, S. S.; Kheswa, B. V.; Shirinda, O.; Khumalo, N.; Bucher, T. D.; Malatji, K. L.
    The spectroscopy of 79 Se is studied via the 82 Se(α, α3n)79Se fusion-evaporation reaction. A negative-parity magnetic dipole band in 79Se is established for the first time. Based on the calculations by the self-consistent tilted axis cranking covariant density functional theory, this new dipole band can be classified as a “stapler” band, which has a relatively stable symmetric prolate deformation as a function of rotational frequency. Hence, it is demonstrated that the stapler bands exist not only in the oblate and triaxial nuclei, but also in prolate nuclei. By examining the angular momentum coupling, it is found that the five valence nucleons in the high-j orbitals play a major role in the closing of the stapler.
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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.