Browsing by Author "Van Rooy, Milton William"

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    An investigation of a possible effect of reactor antineutrinos on the decay rate of 22Na
    (Stellenbosch : Stellenbosch University, 2015-04) Van Rooy, Milton William; Papka, Paul; Smit, F. D.; De Meijer, Robert Johan; Stellenbosch University. Faculty of Science. Dept. of Physics.
    ENGLISH ABSTRACT: Reported claims of a solar neutrino influence on radioactive β - -decay rates prompted a series of three long term measurements that were carried out at the Koeberg nuclear power plant North of Cape Town to investigate the mirror reaction of reactor antineutrinos with a β + - source. The β + -emitter 22Na was exposed to a changing reactor antineutrino flux of the order of ~1012 cm-2 s -1 through the various phases of reactor operation, from off to on or vice versa, to investigate the antineutrino effect on its decay rate. 22Na sources were placed on the face of or inside a scintillation detector while γ-ray energy spectra were measured at source-toreactor-core distances of 17 m and 23 m for reactor unit #1 and unit #2 respectively. The analytical method employed uses ratios of the net-peak count rates of the photopeaks in the γ- ray energy spectra while the antineutrino flux changes during the various phases of reactor operation. These ratios reduce some potential systematic factors such as dead time, but should also remain constant during all phases of reactor operation and be independent of antineutrino flux if antineutrinos have no significant effect on the decay rate of 22Na. Measurement series 1 employed a LaBr3(Ce) detector. Results indicated an effect between reactor-off and –on corresponding to an antineutrino interaction cross section upper limit of the order of barns, assuming that antineutrinos are indeed the cause. Subsequently, two confirmation measurements were performed using a normal (cylindrical) NaI(Tl) detector as well as a NaI(Tl) well-counter. Results of these two measurements did not indicate any correlation with the reactor status. Measurements series 3 proved to be the most sensitive measurement for detecting changes in the decay rate of 22Na and an upper limit of ~10-25 cm 2 was estimated for the cross section of antineutrinos interacting with 22Na. This upper limit is one order of magnitude smaller compared to measurements series 1 and two orders of magnitude smaller compared to measurement series 2. It is also one of magnitude smaller than the effect reported by Jenkins et al. and two orders of magnitude smaller than observed by de Meijer et al. at the Delft reactor. Considering the systematic effects encountered during each measurement series we find no significant evidence for antineutrinos affecting β + -decay in 22Na.
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    Locating the inner edge of a neutron star crust
    (Stellenbosch : University of Stellenbosch, 2010-12) Van Rooy, Milton William; Wyngaardt, Shaun M.; Hillhouse, G. C.; University of Stellenbosch. Faculty of Science. Dept. of Physics.
    ENGLISH ABSTRACT: The overall goal of this project is to study neutron star properties and locate the transition density from the core to the crust using fifteen parameter sets of the effective Skyrme nucleon-nucleon interaction within a method called the dynamical method. Although another approach used to describe nucleon-nucleon interactions called the modified Gogny interaction is briefly discussed in this work, along with a second method for locating the transition density called the thermodynamical method, results using this interaction and method were not generated, but lays some foundation for a PhD project to be undertaken and potentially showing the relation between the interactions and results. The importance of results depends on how well other theoretical approaches to the problem can reproduce those results and to what accuracy. For models to be valid there also has to be good agreement between the theoretical results and known observables. In this project some properties of neutron stars, such as the equation of state, saturation density, binding energy, symmetry energy, slope and incompressibility parameters of symmetry energy are studied. The transition density is located using the dynamical method. Results of the fifteen Skyrme parameter sets show excellent agreement with the published values of the properties of neutron stars and are consistent with their empirical values inferred from nuclear laboratory data, thus validating the use of the Skyrme interactions for describing nuclear matter.