Browsing Department of Physics by browse.metadata.advisor "Bark, R. A."
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- ItemThe development of a β-decay tape station and the search for vibrations in Ruthenium isotopes(Stellenbosch : Stellenbosch University, 2021-03) Makhathini, Lucky Maxwell; Bark, R. A.; Papka, Paul; Rohwer, Erich G.; Van Zyl, J. J.; Stellenbosch University. Faculty of Science. Dept. of Physics.ENGLISH ABSTRACT: This work gives details of the new facility that is introduced to iThemba LABS for nuclear structure studies, called the tape station. The technical description of this device is presented along with an experimental demonstration. A user-friendly control system for this device is developed and it can easily be integrated into the existing beam control system for the iThemba LABS beamline line control systems. Two versions of this device were successfully used to conduct experiments. The versatility of this device is demonstrated by performing multiple experiments, one with a shorter half-life and two with long half-lives. A method to produce "short-lived nuclei (radioactive nuclei)" at iThemba LABS is given. The low-lying states of 98,100Ru were investigated using the γ-ray spectroscopy following the β-decay of 98,100Rh. The source of activity for 162Yb was produced using the 147Sm(19F, 4n) reaction while in 98Ru and 100Ru were produced using the 89Y(12C, 3n)98Rh and 89Y(14N, p2n)100Rh, 89Y(14N, 3n)100Pd reactions at beam energies of 45 MeV and 47 MeV, respectively. The results obtained from experimental data are given and analysed. The 162Yb study demonstrated that this device is capable to be used to probe nuclei with shorter half-lives. While for 100Ru the data confirmed the γ-rays observed in the previous measurement, while in 98Ru new γ-rays were observed. The newly assigned γ and 0+2 bands in 98Ru fit well in the systematics of these excitations assigned in the heavier Ru isotopes while 100Ru differs. Beyond-mean-field calculations employing the self-consistent configuration mixing method suggest that the Ru isotopes are triaxiality deformed and shape coexistence occurs around 98Ru.
- ItemA microscopic description of elastic scattering from unstable nuclei within a relativistic framework(Stellenbosch : Stellenbosch University, 2018-03) Yahya, Wasiu Akanni; Van der Ventel, B. I. S.; Bark, R. A.; Stellenbosch University. Faculty of Science. Dept. of Physics.ENGLISH SUMMARY: In this dissertation, a microscopic study of proton elastic scattering from unstable nuclei at intermediate energies using relativistic formalisms is presented. We have employed both the original relativistic impulse approximation (IA1) and the generalised relativistic impulse approximation (IA2) formalisms to calculate the relativistic optical potentials, with target densities derived from relativistic mean field (RMF) theory using the QHD-II, NL3, and FSUGold parameter sets. Comparisons between the optical potentials computed using both IA1 and IA2 formalisms, and the different RMF Lagrangians are presented for both stable and unstable targets. The comparisons are required to study the effect of using IA1 versus IA2 optical potentials, with different RMF parameter sets, on elastic scattering observables for unstable targets at intermediate energies. We also study the effect of full-folding versus factorized form of the optical potentials on elastic scattering observables. As with the case for stable nuclei, we found that the use of full-folding optical potential improves the scattering observables (especially spin observables) at low intermediate energy (e.g. 200MeV). No discernible difference is found at projectile incident energy of 500 MeV. To check the validity of using localized optical potential, we calculate the scattering observables using non-local potentials by solving the momentum space Dirac equation. The Dirac equation is transformed to two coupled Lippmann-Schwinger equations, which are then numerically solved to obtain the elastic scattering observables. The results are discussed and compared to calculations involving local coordinate-space optical potentials.
- ItemResonance ionization spectroscopy with time of flight mass spectrometry(Stellenbosch : Stellenbosch University, 2019-04) Waso, Frederick John; Steenkamp, Christine M.; Du Plessis, Anton; Bark, R. A.; Stellenbosch University. Faculty of Science. Dept. of Physics.ENGLISH ABSTRACT : Resonance ionization using laser light is one of the most useful techniques for isolating radioactive isotopes and producing radioactive ion beams at accelerator facilities around the world. The aim of this study was to develop an offline experiment for resonance ionization spectroscopy (RIS) using the nonradioactive element tin. Tin was selected as a test element due to its unique nuclear properties and is an element of interest in various nuclear and astrophysical studies. Various properties of the nucleus can impact the atomic energy levels of the atom. Laser spectroscopy can be used to probe and determine these nuclear properties. RIS is one spectroscopic technique that can be used for this purpose. RIS will be used to produce ions of non-radioactive tin and a time-of-flight mass spectrometer (ToF-MS) will be used to detect these ions. Two separate atom sources have been designed and developed, namely a supersonic jet source and an effusive atomic beam source. Due to administrative delays the ToF-MS could not be implemented in the current study. Simulations using the IBSimu simulation library were performed to study and understand the influence of various experimental parameters in an effort to predict optimal parameters for the experimental setup. The impact of the initial volume and velocity distribution of the ions in the atom sources were studied. From the simulations it was observed that a fine margin exists between a too small or too big initial volume. The resolution decreases as the initial volume increases, but at too small volumes space charge effects start to reduce the resolution of the mass spectra as well. It was observed that ions with large transverse velocity components reduce the resolution of the ToF-MS. Proper beam collimation through the use of skimmers can help reduce the transverse velocity spread and improve the resolution of the instrument. The ToF-MS is fitted with an ion reflector called a reflectron. The reflectron greatly improves the resolution of the ToF-MS and is a crucial component to obtain high resolution spectra. From the results it was observed that a linear potential gradient in the reflectron would be optimal for the resolution of the ToF-MS. The two atom sources were compared, and depending on the aim both sources have distinct advantages. The effusive source will be easier to implement and will be ideal to test the sensitivity and resolution of the ToF-MS. The Doppler broadening of the spectral lines in the effusive beam, however, makes selective excitation and ionization impossible. The supersonic jet limits Doppler broadening and is therefore crucial for selective ionization of Sn. The simulations provided an insight into the influence of various experimental parameters that will facilitate the implementation of the ToF-MS at a later stage.