Development of (p,p0γ) detection capabilities at iThemba LABS through the study of low-lying E1 strength in 58Ni

Molaeng, Refilwe Emil
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The principal aim of this study was to explore the (p,p0γ) detection capabilities at 0 ◦ at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) in South Africa. This was done through the study of the low-lying dipole strength of 58Ni with a proton beam of Ep = 80 MeV. The inelastically scattered protons were measured with the K600 magnetic spectrometer positioned at 0◦ , while the subsequent γ decay was measured with the Ball of hyper-pure Germanium and Lanthanum bromide detectors (BaGeL) at backward angles at distances ranging from 17-20 cm away from the target. Low-lying dipole strength, commonly known as the Pygmy Dipole Resonance (PDR), appears in nuclei with neutron excess and can be pictured macroscopically to result from oscillations of these excess neutrons against an inert core with N ' Z. By its nature, the PDR may elucidate the formation of the neutron skin in nuclei. Proton inelastic scattering experiments at very small angles including 0◦ favour electric dipole excitations allowing for the extraction of the full low-lying E1 strength. Detecting these protons in coincidence with the subsequent γ-ray decay further improves the selectivity to very low spin transfer, allowing for resolved excited states between 3 and 10 MeV and multipolarity identification. Moreover, the high-energy resolution high-purity germanium detectors used in decay studies allow for an improvement of the standard energy resolutions obtainable with magnetic spectrometers.
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2022