Modern African nuclear detector laboratory: Development of state-of-the-art in-house detector facility at the University of the Western Cape

The upcoming detector facility aims at developing new state-of-the-art particle detectors as well as providing hands-on training to postgraduate students using both analog and digital signal processing from nuclear radiation detectors. The project is two-fold and aims at developing: 1) ancillary detectors to be coupled with the new GAMKA array at iThemba LABS. Of particular interest to our group is the determination of nuclear shapes, which depend on the hyperfine splitting of magnetic substates; 2) PET scanners for cancer imaging using a cheaper technology. Performance of NaI(Tl) inorganic scintillator detectors has been evaluated using PIXIE-16 modules from XIA digital electronics. Gamma-ray energy spectra were acquired from 60Co and 137Cs radioactive sources to calculate the detector resolution as well as to optimize the digital parameters. The present study focuses on improving and optimizing the slow and fast filter parameters for NaI(Tl) detectors which can eventually be used in the list mode of data aquisition

Observation of the 0+ 2 and γ bands in 98Ru, and shape coexistence in the Ru isotopes

Excited states in 98Ru were investigated using γ-ray spectroscopy following the β-decay of 98Rh, and via the 100Ru(p,t) reaction. Combining the results from the two experiments, two states were revised to have spin-parity of 4+ and subsequently assigned to the 02+ and “γ” bands, respectively. The observed structures in 98Ru are suggested to be deformed and rotational, rather than spherical and vibrational, and fit well into the systematics of these excitations in the Ru isotopes. The 02+ excitation is suggested as a shape coexisting configuration. This observation eliminates some of the last remaining candidates for nearly harmonic vibrational nuclei in the Z≈50 region. Beyond-mean-field calculations are presented that support shape coexistence throughout the Ru isotopes with N=52–62, and suggest a smooth evolution of the shape

Reorientation-effect measurement of the first 2+ state in 12C : Confirmation of oblate deformation

A Coulomb-excitation reorientation-effect measurement using the TIGRESS γ−ray spectrometer at the TRIUMF/ISAC II facility has permitted the determination of the 〈21 +‖E2ˆ‖21 +〉 diagonal matrix element in 12C from particle−γ coincidence data and state-of-the-art no-core shell model calculations of the nuclear polarizability. The nuclear polarizability for the ground and first-excited (21 +) states in 12C have been calculated using chiral NN N4LO500 and NN+3NF350 interactions, which show convergence and agreement with photo-absorption cross-section data. Predictions show a change in the nuclear polarizability with a substantial increase between the ground state and first excited 21 + state at 4.439 MeV. The polarizability of the 21 + state is introduced into the current and previous Coulomb-excitation reorientation-effect analyses of 12C. Spectroscopic quadrupole moments of QS(21 +)=+0.053(44) eb and QS(21 +)=+0.08(3) eb are determined, respectively, yielding a weighted average of QS(21 +)=+0.071(25) eb, in agreement with recent ab initio calculations. The present measurement confirms that the 21 + state of 12C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei

Inelastic scattering of 9Li and excitation mechanism of its first excited state

The first measurement of inelastic scattering of 9Li from deuterons at the ISAC facility is reported. The measured angular distribution for the first excited state confirms the nature of excitation to be an E2 transition. The quadrupole deformation parameter is extracted from an analysis of the angular distribution.Web of Scienc

High resolution 148Nd(3He,nγ) two proton stripping reaction and the structure of the 02 + state in 150Sm

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Study of 0+ States at iThemba LABS

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Shell evolution approaching the N=20 island of inversion : Structure of 26Na

The levels in 26Na with single particle character have been observed for the first time using the d(25Na, pγ) reaction at 5 MeV/nucleon. The measured excitation energies and the deduced spectroscopic factors are in good overall agreement with (0+1)hω shell model calculations performed in a complete spsdfp basis and incorporating a reduction in the N=20 gap. Notably, the 1p3/2 neutron configuration was found to play an enhanced role in the structure of the low-lying negative parity states in 26Na, compared to the isotone 28Al. Thus, the lowering of the 1p3/2 orbital relative to the 0f7/2 occurring in the neighbouring Z=10 and 12 nuclei - 25,27Ne and 27,29Mg - is seen also to occur at Z=11 and further strengthens the constraints on the modelling of the transition into the island of inversion

Multi-quasiparticles and shape-driving effects in "1"2"8Xe, "1"2" 7I and "1"2"5Sb

The "1"2"8X, nucleus is known to be #gamma#-deformed and #gamma#-soft in its ground state. In addition, the K-quantum number, well defined only for axially symmetric deformed nuclei, #gamma##approx#0, is not expected to be such a good quantum number for #gamma#-deformed nuclei. Nevertheless, J"#pi#=K"#pi#=8"- isomers have been observed in the even-Z N=74 isotones, from "1"4"0DY to "1"2"8Xe, as being built on the two quasineutron 7/2"+[404] x 9/2"-[514] orbitals. Therefore, the existence of K-isomerism in "1"2"8Xe, implying the approximate conservation of K, is not well understood. To investigate this phenomenon, "1"2"8Xe has been studied using the fusion-evaporation reaction "1"2"4Sn("9Be,5n)"1"2"8Xe at a beam energy of 58 MeV. Theoretical calculations have been carried out using the configuration constrained blocking method based on a non-axial Woods-Saxon potential and taking both #gamma# and #beta#_2 deformations as dynamical variables. The strong shape-driving effect originated by the J"#pi#=K"#pi#=8"- state as compared with other configurations may explain the existence of K-isomerism in this nucleus. Theoretical predictions are compared with measured hindrance factors and discussed in the context of the #gamma#-softness of this nucleus. In addition, there is an evident lack of information on 3-quasiparticle states in the odd-Z N=74 isotones, where only _5_7"1"3"1La shows evidence of isomerism. The search for 3-quasiparticle states in the odd-Z N=74 isotones and the study of their origin is the other main task of this work. Shape calculations also predict a large #gamma#-deformation and #gamma#-softness for the "1"2"7I ground state and a spherical shape for "1"2"5Sb. These nuclei have been studied using the fusion-evaporation reactions "1"2"4Sn("7Li,#alpha#2n)"1"2"5Sb and "1"2"4Sn("7Li,4n)"1"2"7I at beam energies of 38 and 50 MeV, respectively. Different 3-quasiparticle structures have been identified in "1"2"7I and four isomeric states have been identified in "1"2"5Sb. (author)SIGLEAvailable from British Library Document Supply Centre- DSC:DXN062842 / BLDSC - British Library Document Supply CentreGBUnited Kingdo