Physics and Engineering

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Browsing Physics and Engineering by Author "Bark, R.A."

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    Development of a laser ionization test bench for radioactive ion beams
    (University of Zululand, 2013) Makhathini, Lucky Maxwell; Bark, R.A.; Ndwandwe, O.M.
    This thesis aims to develop the technique for selective laser ionization of atoms and the role it can play in the production of radioactive ion beams. The theory of the production of radioactive ion beams and resonant laser ionization using different techniques will be discussed. Furthermore, the Isotope Separation On-Line method will be comprehensively discussed and the requirements needed for the development of a laser ion source will be summarized. The selective laser ionization of atoms will be demonstrated using two different techniques, laser-enhanced ionization in gas and using a time-of-_flight mass spectrometer. In laser-enhanced ionization in gas, atoms will be ejected into a flame via a device called a nebulizer where the atoms will be excited by two-step excitation followed by collisional ionization in the flame. The signal obtained will be fed onto a "boxcar" for data processing and analysing. In time-of-flight mass spectroscopy, a collimated beam of stable atoms will be created and the detailed design and construction of the atomic beam source and the time-of-flight mass spectrometer will be shown. Two-step ionization of atoms will be used to ionize the created beam and the ionized atoms will be accelerated twice by electric fields, after which they will enter a free-field region and they will be separated according to their mass to charge ratio. The interpretation of the results obtained will conclude the thesis and future prospects for the project will be given.
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    Development of fission suppression devices for afrodite
    (2005) Hlatshwayo, Thulani Thokozani; Bark, R.A.; Ndwandwe, O.M.
    The discovery of the third minimum in various heavy mass nuclei, for example, in the U-Th region, has developed interest in the nuclear physics community to study the behaviour of the nucleus in this minimum. The nuclear shape that is predicted to exist in this minimum is known as a hyperdeformed shape, which corresponds to 3:1 major to minor axis ratio. A hyperdeformed nucleus could be created when a heavy target is bombarded with a light beam, for example, when an a-particle beam bombards 232Th. However in such a reaction, the strongest channel is fission, which occurs almost 99% of the time. Due to the high fission background, which reduces the experimental sensitivity for picking out y decay of hyperdeformed states from the background, many experiments have failed to observe hyperdeformed bands in this minimum. Therefore, this thesis focuses on the development of two fission suppression devices, namely a recoil detector and a solar cell array at iThemba LABS (South Africa).
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    Measurement of the fusion barrier distribution for the 86Kr + 208Pb reaction
    (2005) Ntshangase, Sifiso Senzo; Bark, R.A.
    The main object of this work is to investigate a method of determining the total capture cross-section without passing through separate measurements of quasi-fission, fusion-fission and evaporation residue, using the fact that the sum of the flux in the various final channels is equal to the total incident flux. Thus capture is complementary to the flux reflected from the barrier. Here we present an experiment performed at the cyclotron facility at iThemba LABS to determine the fusion barrier distribution for the ^Kr + 208po reaction using the method of measuring quasi-elastic scattering proposed by Dr. N. Rowley.
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    Radiation Shielding calculations using MCNPX transport code for cost optimization of the shielding material to be used at iThemba LABS.
    (2012) Ngcobo, Phumlani Zipho; Ndwandwe, O.M.; Bark, R.A.
    At iThemba Laboratory for Accelerator Based Sciences (iThemba LABS), the shared use of the Separated Sector Cyclotron has reached the point where further advancement of the respective disciplines cannot be realised. The new facility is proposed to respond to the demands of these, specifically a phased development of Radioactive Ion Beam (RIBs). This facility will include a 70 MeV negative-ion cyclotron with the development of 5 Radioisotope production stations and two production stations for RIBs for nuclear physics and materials science research. The RIB Demonstrator project is suggested to test and demonstrate the advantages of the overall RIB project. The new cyclotron accelerator, which will provide currents of up to 350 μA of 70 MeV protons, has a potential of producing strong sources of ionising radiation. The most challenging entities, which are part of the indirect ionising radiation, are neutral neutrons and photons. There is a need to protect humans and materials from ionising radiation by providing adequate shielding to attenuate these particles, thus bringing their flux to acceptably low levels determined by the International Commission on Radiation Protection (ICRP) for designated personnel accessing this facility. The Monte Carlo for Neutral Particles eXtended (MCNPX) code was used for the purpose of investigating the correct thickness of the shielding of the cyclotron vault and the RIB Demonstrator vault. Results obtained confirmed that 4m and 3m thicknesses of concrete shielding will be adequate in the proposed cyclotron vault and RIB Demonstrator vault respectively.
University of Zululand