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Thesis (Ph. D.)--University of Florida, 1982. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 72-74).

>Magister Scientiae - MSc / This thesis aims at developing a sorting code for Coulomb excitation studies at iThemba LABS. In Coulomb excitation reactions, the inelastic scattering of the projectile transfers energy to the partner nucleus (and vice-versa) through a time-dependent electromagnetic field. At energies well below the Coulomb barrier, the particles interact solely through the well known electromagnetic interaction, thereby excluding nuclear excitations from the process . The data can therefore be analyzed using a semiclassical approximation. The sorting code was used to process and analyze data acquired from the Coulomb excitation of 20Ne beams at 73 and 96 MeV, onto a 194Pt target. The detection of gamma rays was done using the AFRODITE HPGe clover detector array, which consists of nine clover detectors, in coincidence with the 20Ne particles detected with an S3 double-sided silicon detector. The new sorting code includes Doppler-correction effects, charge-sharing, energy and time conditions, kinematics and stopping powers, among others, and can be used for any particle-γ coincidence measurements at iThemba LABS. Results from other Coulomb excitation measurements at iThemba LABS will also be presented.

Philosophiae Doctor - PhD / The Coulomb excitation of 66Ge has been performed for the rst time using \safe" bombarding energies at the HIE-ISOLDE facility at CERN in July 2017. A particle- coincidence experiment using the MINIBALL array and double-sided silicon detectors has allowed the determination of transitional and diagonal matrix elements in 66Ge, yielding new measurements of the reduced transition probability connecting the ground state, 0+1 , and the rst excited state, 2+1 , or B(E2; 2+1 ! 0+1 ) value, and the spectroscopic quadrupole moment of the 2+1 state, QS (2+1 ). A relatively large B(E2) = 29:4(30) W.u. has been extracted using beam-gated data at forward angles { less sensitive to secondorder e ects { as compared with the adopted value of 16:9(7) W.u., but in closer agreement with modern large-scale shell-model calculations using a variety of e ective interactions and beyond-mean eld calculations presented in the current work. / 2022

>Magister Scientiae - MSc / In this work we have determined the spectroscopic or static quadrupole moment of the rst excited state (QS (2+1) lying at 2230.6 keV in 32S using the reorientation e ect. The Coulomb-excitation experiment at safe bombarding energies was performed at iThemba LABS's AFRODITE vault, where 32S beams at 120.3 MeV were bombarded onto a 194Pt target of 1 mg/cm2 thickness. The beam energy has been chosen such that the separation between nuclear surfaces is greater than 6.5 fm at all scattering angles, in order to avoid nuclear interactions. A double-sided CD-type S3 silicon detector, with 24 rings and 32 sectors, has been placed upstream (at backward angles) to detect the scattered particles. Gamma rays have been detected with the AFRODITE clover array. This particle-gamma coincidence experiment allows for an angular distribution and Doppler correction of the gamma rays emitted at 9% the speed of light. The cross sections (or gamma-ray integrated yields) measured as a function of scattering angle at backward angles are sensitive to second-order perturbation e ects in Coulomb excitation, i.e., diagonal matrix elements which are directly related to the spectroscopic quadrupole moment. The gamma-ray integrated yields obtained from this experiment are compared with the GOSIA simulations, yielding a new measurement of QS (2+1) = 􀀀0:10 0:7 eb, which corresponds to a prolate shape in the intrinsic frame of the nucleus. The uncertainty of this measurement is limited by statistics. This result agrees with previous measurements and con rms the zig zag of shapes at the end of the sd shell when approaching the doubly-magic nucleus 40Ca. Nonetheless, the mystery continues as a prolate shape for the rst 2+ disagrees with modern theoretical mean- eld calculations and the pairing coupling model.

Solar wind shocks and the intracluster medium comprise hot, low-density plasmas with few Coulomb collisions. Electrons there are not fluid and so gain and exchange energy by interaction with a variety of plasma waves. We explore two mechanisms for electron energization in such plasmas. In 2D kinetic simulations of solar wind shocks with low beta (magnetic pressure greater than thermal pressure), fast-mode / oblique-whistler waves accelerate electrons in bulk via proton-scale parallel electric fields; electrons’ bulk kinetic energy then converts to heat via magnetic field-aligned electrostatic wave scattering. We show and measure the heating for 2D shocks of varying magnetic obliquity and Mach number, and we qualitatively map the mechanism’s shock parameter regime. Next, consider the intracluster medium: a high-beta plasma (thermal pressure greater than magnetic pressure) in which Megaparsec-scale motions promptly trigger nanoparsec-scale plasma waves, which in turn can scatter 1–100 MeV cosmic ray electrons. Small-scale scattering combined with large-scale motion can heat electrons, and this process is called magnetic pumping. We use 1D simulations of plasma subjected to continuous bulk compression to measure the efficiency of magnetic pumping upon cosmic ray electrons. It is speculated that magnetic pumping may help re-accelerate MeV electrons to radio-emitting energies and so help explain the origin of diffuse, MHz–GHz radio halos enshrouding some clusters of galaxies.

La structure sous-jacente dans la zone A~100, N~60 a été étudié intensivement et extensivement, principalement par décroissance β et spectroscopie γ suite à des réactions de fission. Autour de N~60, en ajoutant juste quelques neutrons, protons un changement de forme rapide des états fondamentaux se produit, allant de sphérique à bien déformé. La coexistence de forme observée dans les noyaux de Sr et Zr est supposée avoir lieu dans toute la région. Les mécanismes impliqués dans l'apparition de la déformation n'étaient pas clairement identifiés. L'interaction entre les orbitales de Nilsson montantes et descendante est évoqué comme l'une des principales raisons du changement de forme. Cependant, une identification claire des orbitales proton et neutron en jeu était nécessaire. A cet effet, l'étude des isotopes ⁹³′⁹⁵′⁹⁷′⁹⁹Rb riches en neutrons a été réalisé excitation Coulombienne au CERN (ISOLDE) en utilisant le post-accélérateur REX-ISOLDE et le dispositif Miniball. Les structures excitées encore inconnues des isotopes ⁹⁷′⁹⁹Rb ont été peuplées et observées. Les coïncidences de transitions γ des états de basse énergie ont été observées et leur corrélations ont permis la construction de schémas de niveaux. Les probabilités de transitions associées ont été extraites grâce code GOSIA. Les éléments de matrice de l'opérateur électromagnétique observées constituent de nouveaux apports afin d'effectuer de nouveaux calculs théoriques permettant de statuer sur les orbitales impliquées. La sensibilité des expériences de ce type peut être accrue en utilisant des faisceaux radioactifs d'ions dont le spin nucléaire est polarisé. La technique de polarisation des feuilles orientées (TFT) fut étudiée dans ce but au CERN. Un nouveau polariseur TFT et un dispositif β-NMR ont être créés et installés après REX-ISOLDE. La connaissance du processus de polarisation associé à la technique reste incomplète à ce jour et de plus amples études sont nécessaires. Des tests préliminaires prometteurs ont été effectués sur le noyau de ⁸Li afin de déterminer le potentiel du dispositif actuel.

The underlying structure in the region A~100, N~60 has been under intensive and extensive investigation, mainly by β-decay and γ-ray spectroscopy from fission processes. Around N~60, by adding just few neutrons, protons a rapid shape change occurs from spherical-like to well deformed g.s. shape. Shape coexistence has been observed in the Sr and Zr nuclei, and is expected to take place in the whole region. The mechanisms involved in the appearance of the deformation is not well understood. The interplay between down-sloping and up-sloping neutron Nilsson orbital is evoked as one of the main reasons for the sudden shape change. However, a clear identification of the active proton and neutron orbitals was still on-going. For that purpose, the neutron rich ⁹³′⁹⁵′⁹⁷′⁹⁹Rb isotopes have been studied by Coulomb excitation at CERN (ISOLDE) using the REX-ISOLDE post-accelerator and the MINIBALL setup. The completely unknown structures of ⁹⁷′⁹⁹Rb have been populated and observed. Prompt γ-ray coincidences of low-lying states have been observed and time correlated to build level schemes. The associated transition strengths have been extracted with the GOSIA code. The observed matrix elements of the electromagnetic operator constituted new inputs of further theoretical calculations giving new insight on the involved orbitals. The sensitivity of such experiment can be increased using nuclear spin polarized RIB. For that purpose the Tilted Foils Technique (TFT) of polarization has been investigated at CERN. A new TFT polarizer with a β-NMR setup have be created and installed after REX-ISOLDE. The uncomplete knowledge of the polarization process associated to the technique needs to be investigated. Conclusive preliminary tests have been performed on ⁸Li in order to determine the potential of the present setup. / La structure sous-jacente dans la zone A~100, N~60 a été étudié intensivement et extensivement, principalement par décroissance β et spectroscopie γ suite à des réactions de fission. Autour de N~60, en ajoutant juste quelques neutrons, protons un changement de forme rapide des états fondamentaux se produit, allant de sphérique à bien déformé. La coexistence de forme observée dans les noyaux de Sr et Zr est supposée avoir lieu dans toute la région. Les mécanismes impliqués dans l'apparition de la déformation n'étaient pas clairement identifiés. L'interaction entre les orbitales de Nilsson montantes et descendante est évoqué comme l'une des principales raisons du changement de forme. Cependant, une identification claire des orbitales proton et neutron en jeu était nécessaire. A cet effet, l'étude des isotopes ⁹³′⁹⁵′⁹⁷′⁹⁹Rb riches en neutrons a été réalisé excitation Coulombienne au CERN (ISOLDE) en utilisant le post-accélérateur REX-ISOLDE et le dispositif Miniball. Les structures excitées encore inconnues des isotopes ⁹⁷′⁹⁹Rb ont été peuplées et observées. Les coïncidences de transitions γ des états de basse énergie ont été observées et leur corrélations ont permis la construction de schémas de niveaux. Les probabilités de transitions associées ont été extraites grâce code GOSIA. Les éléments de matrice de l'opérateur électromagnétique observées constituent de nouveaux apports afin d'effectuer de nouveaux calculs théoriques permettant de statuer sur les orbitales impliquées. La sensibilité des expériences de ce type peut être accrue en utilisant des faisceaux radioactifs d'ions dont le spin nucléaire est polarisé. La technique de polarisation des feuilles orientées (TFT) fut étudiée dans ce but au CERN. Un nouveau polariseur TFT et un dispositif β-NMR ont être créés et installés après REX-ISOLDE. La connaissance du processus de polarisation associé à la technique reste incomplète à ce jour et de plus amples études sont nécessaires. Des tests préliminaires prometteurs ont été effectués sur le noyau de ⁸Li afin de déterminer le potentiel du dispositif actuel.