Browsing by Author "Jongile, Sandile"

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    The Structure of 33Si,35S and the magicity of the N = 20 gap at Z = 14; 16
    (Stellenbosch : Stellenbosch University, 2021-12) Jongile, Sandile; Wiedeking, Mathis; Wyngaart, S.; Sorlin, O.; Lemasson, A.; Papka, Paul; Stellenbosch University. Faculty of Science. Dept. of Physics.
    ENGLISH ABSTRACT: Nuclei along N = 20 provide an excellent region to investigate nuclear structure and interactions, with their evolution from the doubly magic nucleus 40Ca through the Z = 16 and Z = 14 nuclei 36S and 34Si, respectively, to 32Mg with a deformed 2p 􀀀 2h intruder ground state. This study is motivated by and focuses on: i) The robustness of the N = 20 shell gap from 40Ca (studied previously by Matoba et al., [1]) to 36S and 34Si, after removing 4 and 6 protons, respectively. A strong sd-shell closure would lead to a fully occupied neutron d3=2 orbital and no, or little occupancy, neutrons in the p3=2 and f7=2 orbitals located above N = 20. With the deformed 32Mg having only 2 protons removed from 34Si it is an interesting question if the magicity is somewhat gradually or abruptly eroded below Z = 14. ii) A significant reduction of the neutron 1d5=2 and 1d3=2 spin-orbit splitting between 40Ca and 36S, as protons are removed from the 1d3=2 orbital, would be indicative of the effect of proton-neutron tensor force. By comparing the neutron 1d5=2 hole strength between these nuclei, the strength of the tensor force can be probed in an unprecedented manner. Two separate studies were carried out to address the aforementioned motivations. Firstly, an inverse kinematics experiment with the 9Be(34Si,33Si+ )X and 9Be(36S,35S+ )X reactions which was performed at the National Superconducting Cyclotron Laboratory (NSCL) with 98.5 MeV/u 34Si and 88 MeV/u 36S secondary beams produced in the fragmentation of a 48Ca primary beam has been reanalysed. Reaction products were detected with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) coupled to the S800 magnetic spectrometer. This measurement focused on probing the Fermi surface in 34Si and 36S, and locating the strength of the neutron d5=2 orbital. From the spectroscopic factor values, which are derived from observed -ray decays, the neutron 1d3=2 appears to be fully occupied, while some fraction of the 1d5=2 orbital is observed only as the states lie above the neutron emission energy threshold. Secondly, the 36S(p; d)35S reaction is a useful tool to probe the change in neutron spinorbit splitting between 34Si and 36S. The 36S(p; d)35S reaction allows for an investigation into the 36S Fermi surface stiffness and the neutron d3=2 􀀀 d5=2 spin-orbit reduction. It also serves to probe the magicity of 36S through its Fermi surface, complementary to the (d; p) reaction previously performed, reported in Ref. [2]. Of course all this depends on the availability of a reliable 36S target. This was achieved by specifically developing a new target system at iThemba LABS which allows for a cost effective 36S target without heavy contaminants to be used. This novel target, which is in motion and encapsulates sulfur between two Mylar foils, has been shown to be an effective way to produce targets with a significant amount of material (0.5-1 mg/cm2) [3]. Using the developed moving 36S target system with 66 MeV incident protons, states in 35S were populated and studied with the K600 magnetic spectrometer at iThemba LABS. States up to 9 MeV are observed, identifying the neutron single-particle strength below and above the Fermi surface using the detection of the deuterons at the focal plane of the K600 spectrometer with an energy resolution of approximately FWHM = 30 keV in the center of mass.