Muon decay is a unique process involving only the four leptons of the first two generations. This makes it an ideal framework to study the weak interaction. The momentum-angle spectrum of the decay positron can be studied using a general 4-fermion interaction model. Only four parameters are needed in this model to entirely describe the spectrum. The measurement of these four muon decay parameters, rho, eta, delta and Pmu xi, provide a direct test of the Standard Model and its extensions. This thesis presents the final results from the blind analysis of the decay parameter delta using the TWIST (TRIUMF Weak Interaction Symmetry Test) spectrometer. The new precision on the parameter delta is a factor of 11.5 better than the last experimental result prior to TWIST achieving the goal of the TWIST collaboration of an order of magnitude improvement. The challenging parameter eta is also measured from the momentum-angle spectrum for the first time since 1969 with a precision improved by a factor of 7.4. The results are included in a global analysis to obtain stringent limits on some of the coupling constants of the 4-fermion interaction. The result of the measurement of delta are used to evaluate the possibility for a non-local tensor interaction.

Radioactive decay of nuclei via emission of ??-particles is studied using three different theoretical approaches, viz: the quasi-bound state wavefunction approach (QSWA), the superasymmetric ??ssion model (SAFM) and the semiclassical approximation (QCA). The half-lives of the radioactive nuclei, calculated using these methods, are compared with each other and with available experimental data. The resonance wavefunction is obtained by numerically integrating the Schrödinger equation with outgoing boundary conditions. The sensitivity of the calculated decay widths to two particular parameter sets of the Woods-Saxon (WS) optical potentials are studied. Double folding (DF) model calculations to obtain the bare ??-nucleus potential have been carried out with the Reid M3Y effective nucleon-nucleon (NN) interactions. The exchange part of the interaction was taken to be of zero-range pseudo-potential and the density dependence of the NN interaction is accounted for. The effectiveness of the method is demonstrated using both even-even and odd-mass spherical nuclei. / Physics / MSC (PHYSICS)

Estuda-se o transporte de portadores de carga no interior de um isolante dotado de centros profundos de retenção de carga. Supõe-se que os portadores tenham sido depositados na superfície livre do isolante por meio de uma descarga corona rápida e que ai a densidade superficial de carga decaia exponencialmente. Para obter-se o campo elétrico E = E (x,t) no interior do isolante. Integra-se essa equação pelo método das características e obtêm-se expressões analíticas para as linhas de corrente x = x (t,te) (te, designando o tempo de saída da carga da superfície) e para o campo elétrico E = E (t,te) ao longo de cada uma das linhas. São apresentadas famílias de curvas x = x(t,te) e de E = E(t,te),. Eliminando-se graficamente te entre as duas famílias, obtem-se a família de curvas E = E(x) parametrizada em t. Usou-se planímetro para determinar a área debaixo de cada curva E = E(x), e com isso constrói-se a curva de decaimento de potencial / The transport of charge carriers in presence of bulk traps inside an insulator. It is supposed that the carriers were deposited on the surface by a pulse of charge decaying thereafter exponentially with the time. In order to find the electric fielhd electric field E(x,t), the method of characteristics is employed, taking as parameter the time te when the leaves the surface; and ththeir position X=(t,te) and the electric field E=E(x,te) are obtained. By graphicall eliminatination, curves of E(x) are obtained for various times t. A planimeter was used to find the potential at every time as a function of the time

Charged lepton flavour violating processes are highly suppressed in the standard model, but they are predicted to be enhanced in several new physics extensions including supersymmetry and models with leptoquarks or compositeness. Data collected with the BaBar detector at the SLAC PEP-II e$^+$e$^-$ asymmetric collider at a centre-of-mass energy of 10.36~GeV were used to search for electron-muon flavor violation in $\Upsilon (3S)\rightarrow e^{\pm}\mu^{\pm}$ decays. The search was conducted using a data sample in which 118 million $\Upsilon (3S)$ mesons were produced, corresponding to an integrated luminosity of 27~$fb^{-1}$. There is no evidence of a signal in the $\Upsilon (3S)$ data and we report our results as upper limits on $\mathcal{B}(\Upsilon(3S)\rightarrow e^{\pm}\mu^{\mp})<3.6\times10^{-7}\mathrm{at~ 90\%~ CL}$. / Graduate

>Magister Scientiae - MSc / The study of ²²Na beta decay offers an opportunity to test the Standard Model of Particle Physics via measurements of the β−γ angular correlation. A previous measurement of this correlation yielded a non-zero value, indicating the need for a higher-order matrix element to the decay, beyond the allowed V − A approximation. On assuming the Conserved Vector Current (CVC) hypothesis for weak interactions and using the magnetic dipole M1 width of the analog 2+ state in ²²Na, one obtains an unexpectedly large 'second-class' form factor for 22Na β decay that is in disagreement with the Standard Model prediction. This thesis describes an analysis of data obtained from a previous ²¹Ne(p, γ) experiment to obtain the M1 width of the 2+ state of interest in ²²Na. This work aims to use the M1 width and the independently measured of the β − γ angular correlation to obtain a higher-order Standard-Model-allowed weak magnetism form factor for the decay, in an attempt to explain the observed anomaly mentioned above. / National Research Foundation (NRF)

Litchi (Litchi chinensis Sonn.) is a commercially valued fruit mainly for its attractively red pericarp and exotic taste. However, the market value of the fruit is affected by pericarp browning, desiccation and postharvest decay. Current control measures include sulphur dioxide (SO2) fumigation, low temperature storage and high relative humidity (RH). Sulphur residues on fruit, moisture loss, altered taste and decay caused by Penicillium spp., limit the use of SO2 fumigation. Technology that can provide a potential alternative method to retain the quality of fruit is modified atmosphere packaging (MAP). In this study (Chapter 3), the effect of active and passive modified atmospheres on quality retention of litchi cultivars ‘Mauritius’ and ‘McLean’s Red’ was investigated. Results indicated that ‘McLean’s Red’ is more suitable for MAP technology than ‘Mauritius’. Lidding film–4 holes significantly reduced activity of oxidation enzymes, polyphenol oxidase (PPO) and peroxidase (POD), and retained higher pericarp colour. Lidding film–10 holes retained soluble solids concentration to titratable acidity ratio (SSC/TA) (~65), thereby preventing the loss of taste and litchi fruit flavour. In order to enhance the MAP technology further (Chapter 4), chitosan coating of fruit was also assessed. Chitosan (1.0 g L-1) combined with MAP effectively prevented decay, browning and pericarp colour loss in ‘McLean’s Red’. Chitosan (1.0 g L-1) integrated with MAP reduced PPO and POD activity, retained membrane integrity, anthocyanin content and pericarp colour. ‘McLean’s Red’ was found to be more suitable for the chitosan (1.0 g L-1) and MAP integrated treatment than ‘Mauritius’ in retaining overall quality. In addition, the effect of 1-methylcyclopropene (1-MCP) in combination with MAP was determined for both cultivars (Chapter 5). In this case 1-MCP (300 nL L-1) was most effective in preventing browning and retaining colour in both cultivars after 14 and 21 days of cold storage. The effect of 1-MCP (300 nL L-1) showed more potential on ‘McLean’s Red’ than ‘Mauritius’. At higher concentrations (500 and 1000 nL L-1), 1-MCP showed negative effects on membrane integrity, pericarp browning, PPO and POD activity in both cultivars. The effect of integrated postharvest treatments i.e. modified atmosphere packaging combined with chitosan and integrated MAP and 1-MCP as well as MAP and chitosan coating on foodborne bacterial pathogens (Escherichia coli O157:H7 and Staphylococcus aureus) spike-inoculated on litchi fruit surfaces, and Penicillium spp. decay were also investigated (Chapter 6). Results showed integrated MAP and chitosan (0.1 g L-1 and 1.0 g L-1) treatments significantly reduced high and low inoculums load of E. coli O157:H7 and S. aureus on litchi fruit after 21 days of cold storage. Integrated MAP and 1000 nL L-1 1-MCP resulted in higher disease severity. Integrated MAP and chitosan (0.1 g L-1 and 1.0 g L-1) treatments showed very good decay control. The total microbial population of the litchi fruit surface was also determined. Integrated MAP and 1.0 g L-1 significantly reduced the total microbial flora after 21 days of cold storage. / Dissertation (MSc)--University of Pretoria, 2010. / Microbiology and Plant Pathology / unrestricted

The directional correlation of the 346-136 Kev gamma-gamma cascade in Ta¹⁸¹ was measured using the delayed coincidence method with a source of Hf¹⁸¹ in 27 N HF. The contributions to the composite delayed coincidence spectrum of the interfering 133-482 Kev and 133 - 346 Kev cascades were removed by the subtraction from this spectrum of appropriate 133-482 Kev pure delayed coincidence data. The extracted 346 -136 Kev coincidence data then yielded the correlation coefficients A₂₂ = o.190 土0.011 and A₄₄. = -0.025 土O. 024 that are consistent with the established spin sequence 5/ 2(E2)9 / 2(Ml +E2)7 / 2 and with an admixture of 16.20/0土1. 2% E2 radiation in the 136 Kev mixed transition. The results of the experiment are in excellent agreement with those obtained from conversion electron measurements and resolve the discrepancy apparent in earlier work on the 346-136 Kev cascade

The investigation of isomeric states in neutron-rich nuclei provides useful insights into the underlying nuclear configurations, and understanding their occurrence along an isotopic chain can inform about shell evolution. Recent studies on neutron-rich Si isotopes near the magic number N = 20 and approaching N = 28 have revealed the presence of low-lying states with intruder configurations, resulting from multiple-particle, multiple-hole excitations across closed shell gaps. The characterization of these states involves measuring their half-lives and transition probabilities. In this study, a new low-energy (7/2−1) isomer at 68 keV in 37Si was accessed via beta decay and characterized. To achieve this, radioactive 37Al and 38Al ions were produced through the projectile fragmentation reaction of a 48Ca beam and implanted into a CeBr3 detector, leading to the population of states in 37Si. The 68-keV isomer was directly populated in the beta-delayed one neutron emission decay of implanted 38Al ions. Ancillary detector arrays comprising HPGe and LaBr3(Ce) detectors were employed for the detection of beta-delayed gamma rays. The choice of detectors was driven by their excellent energy and timing resolutions, respectively. The beta-gamma timing method was utilized to measure the half-life of the new isomeric state in 37Si. This dissertation also discusses other timing techniques employed to search for and characterize isomeric states following beta decay of implanted ions. Notably, the half-life of the newly observed (7/2−1) isomeric state in 37Si was measured to be 9.1(7) ns. The half-life of the previously observed closely-lying (3/2−1) state at 156 keV was determined to be 3.20(4) ns, consistent with previously reported values. Reduced ground-state transition probabilities associated with the gamma-ray decay from these excited states were in agreement with results obtained from shell model calculations. In addition to the investigation of isomeric states in 37Si, isomeric 0+ states in 34Si and 32Mg nuclei belonging to the N = 20 “island of inversion” were characterized and searched for, respectively. The isomeric 0+ state in 34Si was populated following the beta decay of implanted 34Mg ions and its 34Al daughter nucleus. Similarly, the 0+ state in 32Mg was searched for via the beta-delayed one neutron emission decay of implanted 33Na ions.

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We apply anisotropic Banach space methods together with operator renewal theory to obtain polynomial rates of decay of correlations for a class of generalized baker's transformations. The polynomial rates were proved for a smaller class of observables in a 2013 paper of Bose and Murray by fundamentally different methods. Our approach provides a direct analysis of the Frobenius-Perron operator associated to a generalized baker's transformation in contrast to the paper of Bose and Murray where decay rates are obtained for a factor map and lifted to the full map. / Graduate