Browsing by Author "Smit, F. D."

Now showing 1 - 8 of 8
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    Characterization of the proposed 4−α cluster state candidate in ¹⁶O
    (American Physical Society, 2017) Li, K. C. W.; Neveling, R.; Adsley, P.; Papka, P.; Smit, F. D.; Brummer, J. W.; Diget, C. Aa.; Freer, M.; Harakeh, M. N.; Kokalova, Tz.; Nemulodi, F.; Pellegri, L.; Rebeiro, B.; Swartz, J. A.; Triambak, S.; Van Zyl, J. J.; Wheldon, C.
    The 0¹⁶O(α,α′) reaction was studied at θlab=0∘ at an incident energy of Elab=200 MeV using the K600 magnetic spectrometer at iThemba LABS. Proton decay and α decay from the natural parity states were observed in a large-acceptance silicon strip detector array at backward angles. The coincident charged-particle measurements were used to characterize the decay channels of the 0⁺₆ state in ¹⁶O located at Ex=15.097(5) MeV. This state is identified by several theoretical cluster calculations to be a good candidate for the 4−α cluster state. The results of this work suggest the presence of a previously unidentified resonance at Ex≈15 MeV that does not exhibit a 0⁺ character. This unresolved resonance may have contaminated previous observations of the 0⁺₆ state.
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    Deformation dependence of the isovector giant dipole resonance : the neodymium isotopic chain revisited
    (Elsevier, 2018) Donaldson, L. M.; Bertulani, C. A.; Carter, J.; Nesterenko, V. O.; Von Neumann-Cosel, P.; Neveling, R.; Ponomarev, V. Yu; Reinhard, P. G.; Usman, I. T.; Adsley, P.; Brummer, J. W.; Buthelezi, E. Z.; Cooper, G. R. J.; Fearick, R. W.; Fortsch, S. V.; Fujita, H.; Fujita, Y.; Jingo, M.; Kleinig, W.; Kureba, C. O.; Kvasil, J.; Latif, M.; Li, K. C. W.; Mira, J. P.; Nemulodi, F.; Papka, P.; Pellegri, L.; Pietralla, N.; Richter, A.; Sideras-Haddad, E.; Smit, F. D.; Steyn, G. F.; Swartz, J. A.; Tamii, A.
    Proton inelastic scattering experiments at energy Ep=200MeV and a spectrometer scattering angle of 0° were performed on 144,146,148,150Nd and 152Sm exciting the IsoVector Giant Dipole Resonance (IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, 150Nd and 152Sm, exhibit a pronounced asymmetry rather than a distinct double-hump structure expected as a signature of K-splitting. This behaviour may be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data.
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    Indirect study of the stellar ³⁴ Ar(α,p) ³⁷K reaction rate through ⁴⁰Ca(p,t) ³⁸Ca reaction measurements
    (American Physical Society, 2017) Long, A. M.; Adachi, T.; Beard, M.; Berg, G. P. A.; Buthelezi, Z.; Carter, J.; Couder, M.; deBoer, R. J.; Fearick, R. W.; Fortsch, S. V.; Gorres, J.; Mira, J. P.; Murray, S. H. T.; Neveling, R.; Papka, P.; Smit, F. D.; Sideras-Haddad, E.; Swartz, J. A.; Talwar, R.; Usman, I. T.; Wiescher, M.; Van Zyl, J. J.; Volya, A.
    The ³⁴Ar(α,p)³⁷K reaction is believed to be one of the last in a sequence of (α,p) and (p,γ) reactions within the Tz=−1, sd-shell nuclei, known as the αp-process. This process is expected to influence the shape and rise times of luminosity curves coming from type I x-ray bursts (XRBs). With very little experimental information known on many of the reactions within the αp-process, stellar rates are calculated using a statistical model, such as Hauser-Feshbach. Questions on the applicability of a Hauser-Feshbach model for the ³⁴Ar(α,p) ³⁷K reaction arise due to level density considerations in the compound nucleus, 38Ca. We have performed high energy-resolution forward-angle ⁴⁰Ca(p,t)³⁸Ca measurements with the K=600 spectrograph at iThemba LABS in order to identify levels above the α-threshold in ³⁸Ca. States identified in this work were then used to determine the ³⁴Ar(α,p)³⁷K reaction rate based on a narrow-resonance formalism. Comparisons are made to two standard Hauser-Feshbach model predicted rates at XRB temperatures.
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    Rotational 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.
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    Search for highly excited states in ²⁸Si
    (IOP Publishing, 2017) Montanari, D.; Courtin, S.; Jenkins, D. G.; Diget, C.; Yavuzkanat, N.; Neveling, R.; Mira, J. P.; Nemulodi, F.; Smit, F. D.; Usman, I.; Papka, P.; Swartz, J. A.; Van Zyl, J. J.; Orce, N.
    The theoretical and experimental determination of superdeformed states in nuclei in the mass region A≤40 has been since a long time one of the major challenges of nuclear structure studies. Despite the considerable experimental and theoretical work dedicated to this topic, up to now superdeformed bands have been found in only two nuclei, ³⁶Ar and ⁴⁰Ca. While the experimental signature of the superdeformed nature of those states is irrefutable, their theoretical interpretation is still uncertain. In particular, it is not clear whether clusterisation is responsible of the onset of superdeformation. For this reason, we wanted to investigate an even lighter system, ²⁸Si, where a number of theoretical calculations predict the presence of superdeformation as an effect of the cluster structure of the nucleus.
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    Second T = 3/2 state in 9B and the isobaric multiplet mass equation
    (American Physical Society, 2018) Mukwevho, N. J.; Rebeiro, B. M.; Marin-Lambarri, D. J.; Triambak, S.; Adsley, P.; Kheswa, N. Y.; Neveling, R.; Pellegri, L.; Pesudo, V.; Smit, F. D.; Akakpo, E. H.; Brümmer, J. W.; Jongile, S.; Kamil, M.; Mabika, P. Z.; Nemulodi, F.; Orce, J. N.; Papka, P.; Steyn, G. F.; Yahia-Cherif, W.
    Recent high-precision mass measurements and shell-model calculations [M. Brodeur et al., Phys. Rev. Lett. 108, 212501 (2012)] have challenged a longstanding explanation for the requirement of a cubic isobaric multiplet mass equation for the lowest A=9 isospin quartet. The conclusions relied upon the choice of the excitation energy for the second T=3/2 state in 9B, which had two conflicting measurements prior to this work. We remeasured the energy of the state using the 9Be(3He,t) reaction and significantly disagree with the most recent measurement. Our result supports the contention that continuum coupling in the most proton-rich member of the quartet is not the predominant reason for the large cubic term required for A=9 nuclei.
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    Wavelet signatures of K-splitting of the Isoscalar Giant Quadrupole Resonance in deformed nuclei from high-resolution (p, p ) scattering off ¹⁴⁶,¹⁴⁸,¹⁵⁰Nd
    (Elsevier, 2018) Kureba, C. O.; Buthelezi, Z.; Carter, J.; Cooper, G. R. J.; Fearick, R. W.; Fortsch, S. V.; Jingo, M.; Kleinig, W.; Krugmann, A.; Krumbolz, A. M.; Kvasil, J.; Mabiala, Justin; Mira, J. P.; Nesterenko, V. O.; Von Neumann-Cosel, P.; Neveling, R.; Papka, P.; Reinhard, P. G.; Richter, A.; Sideras-Haddad, E.; Smit, F. D.; Steync, G. F.; Swartz, J. A.; Tamii, A.; Usman, I. T.
    The phenomenon of fine structure of the Isoscalar Giant Quadrupole Resonance (ISGQR) has been studied with high energy-resolution proton inelastic scattering at iThemba LABS in the chain of stable even-mass Nd isotopes covering the transition from spherical to deformed ground states. Awavelet analysis of the background-subtracted spectra in the deformed 146,148,150Nd isotopes reveals characteristic scales in correspondence with scales obtained from a Skyrme RPA calculation using the SVmas10 parameterization. Asemblance analysis shows that these scales arise from the energy shift between the main fragments of the K=0, 1and K=2components.
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    α clustering in ²⁸Si probed through the identification of high-lying 0⁺ states
    (American Physical Society, 2017) Adsley, P.; Jenkins, D. G.; Cseh, J.; Dimitriova, S. S.; Brummer, J. W.; Li, K. C. W.; Marin-Lambarri, D. J.; Lukyanov, K.; Kheswa, N. Y.; Neveling, R.; Papka, P.; Pellegri, L.; Pesudo, V.; Pool, L. C.; Riczu, G.; Smit, F. D.; Van Zyl, J. J.; Zemlyanaya, E.
    Background: Aspects of the nuclear structure of light α-conjugate nuclei have long been associated with nuclear clustering based on α particles and heavier α-conjugate systems such as ¹²C and ¹⁶O. Such structures are associated with strong deformation corresponding to superdeformed or even hyperdeformed bands. Superdeformed bands have been identified in ⁴⁰Ca and neighboring nuclei and find good description within shell model, mean-field, and α-cluster models. The utility of the α-cluster description may be probed further by extending such studies to more challenging cases comprising lighter α-conjugate nuclei such as ²⁴Mg, ²⁸Si, and ³²S. Purpose: The purpose of this study is to look for the number and energy of isoscalar 0⁺ states in ²⁸Si. These states are the potential bandheads for superdeformed bands in ²⁸Si corresponding to the exotic structures of ²⁸Si. Of particular interest is locating the 0⁺ bandhead of the previously identified superdeformed band in ²⁸Si. Methods: α-particle inelastic scattering from a natSi target at very forward angles including 0∘ has been performed at the iThemba Laboratory for Accelerator-Based Sciences in South Africa. Scattered particles corresponding to the excitation energy region of 6 to 14 MeV were momentum-analysed in the K600 magnetic spectrometer and detected at the focal plane using two multiwire drift chambers and two plastic scintillators. Results: Several 0⁺ states have been identified above 9 MeV in ²⁸Si. A newly identified 9.71 MeV 0⁺ state is a strong candidate for the bandhead of the previously discussed superdeformed band. The multichannel dynamical symmetry of the semimicroscopic algebraic model predicts the spectrum of the excited 0⁺ states. The theoretical prediction is in good agreement with the experimental finding, supporting the assignment of the 9.71-MeV state as the bandhead of a superdeformed band. Conclusion: Excited isoscalar 0⁺ states in ²⁸Si have been identified. The number of states observed in the present experiment shows good agreement with the prediction of the multichannel dynamical symmetry.