Publications (11)19.47 Total impact
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Article: Close near-degeneracy in a pair of four-quasiparticle bands in 194Tl
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ABSTRACT: A pair of rotational bands associated with the configuration at lower spins and with the configuration at higher spins is found in 194Tl. 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. Such close near-degeneracy probably indicates chiral geometry in the angular momentum space.Physics Letters B 01/2013; · 3.95 Impact Factor -
Dataset: Candidate chiral bands in 198Tl
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Article: Candidate chiral bands in 198Tl
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ABSTRACT: High-spin states in 198Tl were studied using the 197Au(a \alpha, 3n) reaction. The level scheme was considerably extended including two new bands and several non-yrast levels. One of the new bands is possibly a chiral partner to the yrast p \pi h 9/2⊗ n \nu i 13/2 -1band. Two-quasiparticle-plus-triaxial-rotor model calculations suggest an aplanar orientation of the total angular momenta for these bands, thus supporting possible chirality.European Physical Journal A 04/2012; 45(1):39-50. · 2.19 Impact Factor -
Article: Nonzero quadrupole moments of candidate tetrahedral bands.
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ABSTRACT: Negative-parity bands in the vicinity of 156Gd and 160Yb have been suggested as candidates for the rotation of tetrahedral nuclei. We report the observation of the odd and even-spin members of the lowest energy negative-parity bands in 160Yb and 154Gd. The properties of these bands are similar to the proposed tetrahedral band of 156Gd and its even-spin partner. Band-mixing calculations are performed and absolute and relative quadrupole moments deduced for 160Yb and 154Gd. The values are inconsistent with zero, as required for tetrahedral shape, and the bands are interpreted as octupole vibrational bands. The failure to observe the in-band E2 transitions of the bands at low spins can be understood using the measured B(E1) and B(E2) values.Physical Review Letters 01/2010; 104(2):022501. · 7.37 Impact Factor -
Article: Proton capture to continuum states of^{209} Bi
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ABSTRACT: High resolution spectra from fast proton radiative capture in 208Pb are presented for three energies of the incident protons: 14.8, 15.7, and 16.9 MeV. The collected spectra were analyzed with emphasis on the region of capture to unbound states in order to search for possible structure and to study the competition between two basically different phenomena: the statistical process versus the fluctuation effects in radiative capture to unbound final states. In the energy region of incoming protons considered in our experiment, the statistical processes modeled with a Hauser-Feshbach calculation dominate. The spectra of primary γ rays, coincident with the low energy one from the decay of the f7/2 single-particle state, show a prominent structure which is predominantly of g9/2 character. The calculations of continuum spectra based on the extended direct-semidirect model and the Hauser-Feshbach statistical approach successfully reproduce the experimental data.Phys. Rev. C. 04/2006; 73(4). -
Article: Capture cross sections for very heavy systems
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ABSTRACT: In intermediate-mass systems, collective excitations of the target and projectile can greatly enhance the subbarrier capture cross section σ cap by giving rise to a distribution of Coulomb barriers. For such systems, capture essentially leads directly to fusion [formation of a compound nucleus (CN)], which then decays through the emission of light particles (neutrons, protons, and alpha particles). Thus, the evaporation-residue (ER) cross section is essentially equal to σ cap. For heavier systems, the experimental situation is significantly more complicated owing to the presence of quasifission (QF) (rapid separation into two fragments before the CN is formed) and by fusion-fission (FF) of the CN itself. Thus, three cross sections need to be measured in order to evaluate σ cap. Although the ER essentially recoil along the beam direction, QF and FF fragments are scattered to all angles and require the measurement of angular distributions in order to obtain the excitation function and barrier distribution for capture. Two other approaches to this problem exist. If QF is not important, one can still measure just the ER cross section and try to reconstruct the corresponding σ cap through use of an evaporation-model code that takes account of the FF degree of freedom. Some earlier results on σ cap obtained in this way will be reanalyzed with detailed coupled-channels calculations, and the “extra-push” phenomenon discussed. One may also try to obtain σ cap by exploiting unitarity, that is, by measuring instead the flux of particles corresponding to quasielastic (QE) scattering from the Coulomb barrier. Some new QE results obtained for the 86Kr + 208Pb system at iThemba LABS in South Africa will be presented.Physics of Atomic Nuclei 01/2006; 69(7):1093-1100. · 0.57 Impact Factor -
Article: Aspects of nuclear physics research at iThemba LABS, South Africa
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ABSTRACT: A summary of recent results of research at iThemba LABS is given. This includes high-resolution measurements of the fine structure of isoscalar giant quadrupole resonances, a new programme to measure fusion barrier distributions for reactions leading to the formation of superheavy elements, measurements of high-energy γ-rays from (p,γ) reactions using the AFRODITE array of HpGe clover detectors, and a comparison of the vibrational band structures of 160Yb, measured with the AFRODITE array, with the X(5)-β2n model. A summary of future developments is given.Journal of Physics G Nuclear and Particle Physics 09/2005; 31(10):S1747. · 4.18 Impact Factor -
Article: Candidate chiral bands in
http://dx.doi.org/10.1140/epja/i2010-10994-x. -
Article: Barrier distribution for a ‘superheavy’ nucleus–nucleus collision
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ABSTRACT: Large-angle quasielastic scattering has been studied in a high-Z1Z2 nuclear reaction of the type leading to superheavy-element production by cold fusion. We show that despite the presence of strongly dissipative channels, and the complete absence of fusion, the notion of an external barrier distribution, determined by strong coupling to collective excitations of target and projectile, is still valid. Furthermore, our method allows us to deduce some properties of the deep-inelastic processes in this system.Physics Letters B. -
Article: Measuring high-energy γ-rays with Ge clover detectors
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ABSTRACT: Gamma-rays with energies up to 20.7 MeV produced by the capture reaction were measured with the AFRODITE germanium detector array. The measured full energy peak efficiency of the array is 1.5% at 1.3 MeV and 9(2)×10-4 at 15 MeV. The FWHM of capture γ-ray peaks was 50 keV up to the highest measured energies. The efficiency curve has been calculated using a Monte-Carlo simulation code GEANT. The simulation and measurements agree very well.Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 557(2):523-527. · 1.21 Impact Factor -
Article: Possible chirality in the doubly-odd^{198} Tl nucleus: Residual interaction at play
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ABSTRACT: A candidate for chiral bands was found in 198Tl for the first time in a mass region of oblate (or nonaxial with γ⩾30°) deformed nuclei. Two bands show very similar quasiparticle alignments, moments of inertia, and B(M1)/B(E2) ratios. They have a relative excitation energy of about 500 keV and different patterns of energy staggering. Calculations using the two-quasiparticle-plus-triaxial-rotor model with residual proton-neutron interaction included show that a triaxial deformation with γ~44° agrees very well with all the experimental observations. Furthermore, considerable energy staggering for both partner bands was calculated for this πh9/2⊗νi13/2-1 configuration at γ~30°, suggesting that chiral bands may have substantial energy staggering.Phys. Rev. C. 78(2).
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Institutions
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2012
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University of Cape Town
Cape Town, Province of the Western Cape, South Africa
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2005
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iThemba Labs - Laboratory for Accelerator Based Science
Cape Town, Province of the Western Cape, South Africa
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