Thesis (PhD)--Stellenbosch University, 2015. / 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. / AFRIKAANSE OPSOMMING: Berigte bewerings van son-afkomstige neutrinos se invloed op β - -verval het gelei tot drie lang termyn metings wat uitgevoer is by die Koeberg kernkrag stasie Noord van Kaapstad om die spieëldbeeld reaksie van antineutrinos met ‘n β + -bron te ondersoek. Die 22Na β + -bron is blootgestel aan ‘n veranderende reaktor antineutrino vloed van die order ~1012 cm -2 s -1 soos die reaktor deur verskeie fases van operasie gaan, vanaf afgeskakel na aangeskakel of omgekeerd, om die effek van antineutrinos op die bron se vervaltempo te ondersoek. 22Na bronne was teen die voorkant of binne ‘n sintillator detektor geplaas terwyl γ-straal energie spektra gemeet was by bron-tot-reaktor kern afstande van 17 m en 23 m vir reaktor eenheid #1 en #2 afsonderlik. Die analitiese metode gebruik verhoudings van die netto-piek teltempos van die fotopieke in die γ-straal energie spektra terwyl die antineutrino vloed verander tydens verskeie fases van reaktor operasie. Hierdie verhoudings verminder sekere potensiële systematiese effekte soos dooietyd en moet konstant bly tydens alle fases van reaktor operasie en moet ook onafhanklik wees van die antineutrino vloed indien antineutrinos geen effek het op die vervaltempo van 22Na nie. Die eerste reeks metings het gebruik gemaak van ‘n LaBr3(Ce) detektor. Resultate het ‘n effek getoon tussen reaktor-af en reaktor-aan wat ooreenstem met ‘n boonste limiet vir die interaksie kansvlak van antineutrinos met grootteorde van barns, indien antineutrinos wel die oorsaak is. Twee reekse van opvolgende metings is uitgevoer wat gebruik gemaak het van ‘n gewone (silindriese) NaI(Tl) detektor asook ‘n NaI(Tl) put detektor. Resultate van hierdie metings het geen korrelasie met die reaktor status gewys nie. Die derde reeks metings was die sensitiefste om veranderinge in die verval tempo van 22Na te wys en ‘n boonste limiet vir die interaksie kansvlak van antineutrinos op 22Na was beraam as ~10-25 cm 2 . Hierdie boonste limiet is een grootteorde kleiner in vergelyking met reeks 1 en twee grootteordes kleiner as reeks 2. Dit is ook een grootteorde kleiner as die waarde van Jenkins et al. en twee grootteordes kleiner as wat de Meijer et al. berig het by die Delft reaktor. In agneming van die systematise probleme wat ondervind was tydens die drie reeks metings vind ons geen beduidende effek van antineutrinos op die vervaltempo van 22Na nie.

No description available.

In this thesis, I present the theory of neutrinoless double-beta decay (0 2 ), particularly the theory of exotic modes of 0 2 involving the emission of one or two Majorons. Alongside this, I summarise the most recent results in the experimental search for 0 2 , including limits on the rate of these exotic processes. I describe the SNO+ experiment and it's physics goals, which include the search for 0 2 . As part of the SNO+ collaboration, I have made a signi cant contribution towards the development of the data quality software that is essential for ensuring SNO+ can achieve its physics goals-including in 0 2 searches. I describe how I developed a software package that performs the high-level data quality checks. Continuing with the software theme, I then describe a python-based limit-setting and tting software package called echidna. I have been a lead developer of echidna as part of my PhD, so I describe the software in detail and how it can be used to set limits on 0 2 signals. By reproducing the sensitivity results of the KamLAND-Zen experiment, in four key Majoronemitting 0 2 modes, I verify the use of echidna as a limit-setting tool for this type of search. Finally, I present the results of a comprehensive sensitivity study, where I determine the potential sensitivity of SNO+ to the same set of Majoron-emitting modes that KamLAND-Zen and other 0 2 experiments have already investigated.

No description available.

As part of a research program to study the transitional region of N=88 isotones, ¹⁵²Tb was produced by the reaction ¹⁵¹Eu(α,3n)¹⁵²Tb in the 88" cyclotron located at LBNL. Gamma-ray spectroscopy of the radiation emitted from excited ¹⁵²Gd following the β⁺ decay of ¹⁵²Tb has been performed using an array of 20 germanium detectors. The large Q-value (3990 keV) of the ¹⁵²Tb 2⁻ decay allows for the population of many levels; study of coincidence and single events resulted in the establishment of 54 new levels and 266 new transitions. Angular correlation of the coincidences has determined spin and parity of many levels with several seen as key to the band structure, including two new 0⁺ levels. One new rotational band including the new 1475.2 keV 0⁺ level and the 1771.7 keV 2⁺ level is proposed. The overall band structure compared to collective excitation models demonstrates the position of ¹⁵²Gd in the transition from a spherical to deformed shape, also seen in other N=88 isotones. Monopole transition strength among bands indicates the possibility of mixing of both shapes among the excited states. The remarkable similarity of the band structure among these isotones is discussed. / Graduation date: 2005

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, December 2003. / Includes bibliographical references. Also available on the Internet.

In this thesis I present research in neutrino physics utilizing tools from both atomic physics and astrophysics. Recent advances in atomic physics enable a new type of beta decay experiment to measure the absolute mass scale of the neutrino using a sample of ultracold atomic tritium. These initial conditions enable the detection of the helium ion in coincidence with the beta. I construct a two-dimensional fit incorporating both the shape of the beta spectrum and the direct reconstruction of the neutrino mass peak. I present simulation results of the feasible limits on the neutrino mass achievable in this new type of tritium beta decay experiment. The same advances in atomic physics that enable the creation of an atomic source for tritium beta decay also suggest a new method of achieving large-scale isotope separation. Multiple experiments that are investigating the absolute mass scale of the neutrino through neutrinoless double beta decay could benefit from this new technique, which applies generally to many elements, including the double beta emitter Nd-150 that is particularly difficult to separate in large quantities. The method is based on an irreversible change of the mass-to-magnetic moment ratio of a particular isotope in a supersonic atomic beam, followed by a magnetic multipole whose gradients deflect and guide the atoms. I present numerical simulations of isotope separation for a range of examples and demonstrate that large-scale isotope separation should be possible using ordinary inexpensive magnets and the existing technologies of supersonic beams and lasers. Additionally I report results from a search for low-multiplicity neutrino bursts in the Sudbury Neutrino Observatory (SNO). Such bursts could indicate detection of a nearby core-collapse supernova explosion. The data were taken from November 1999 to May 2001 when the detector was filled with heavy water (Phase I), as well as data from July 2001 to August 2003 when NaCl was added to the detector (Phase II). The search was a blind analysis in which the potential backgrounds were estimated and analysis cuts were developed to eliminate such backgrounds with 90% confidence before the data were examined. The search maintained a greater than 50% detection probability for standard supernovae occurring at a distance of up to 60 kpc for Phase I and up to 70 kpc for Phase II. No low-multiplicity bursts were observed during the data-taking period. / text

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A solid-state DE-E telescope beta spectrometer has been built and used to study beta-minus spectra. The system consists of a 15 mm x 500 mm$ sp2$ hyperpure germanium (HPGe) E-detector and a 300 $ mu$m x 200 mm$ sp2$ Si DE-detector with a special "keyhole" design. / The response function of the system has been determined experimentally using mono-energetic electron beams with incident energies ranging from 1 to 12 MeV. / The beta endpoint energies of 25 nuclei, namely, $ sp{32}$P, $ sp{88}$Rb, $ sp{91-99}$Rb, $ sp{91-96}$Sr, $ sp{99-100}$Sr, $ sp{92-96}$Y and $ sp{100}$Y have been measured. The Q-beta values and mass excesses for A = 91-100 have been determined. The results for $ sp{99}$Rb, $ sp{99-100}$Sr and $ sp{100}$Y have been obtained for the first time. / The beta strength functions for odd mass Rb isotopes, namely $ sp{91-99}$Rb have been measured for the first time from direct beta spectroscopy with a solid-state telescope system. The experimental results have been compared to calculations using the Brown-Bolsterli (B-B) model.

An accurate response function for a superconducting solenoid beta spectrometer for electrons up to 5.5 MeV has been found using Monte Carlo calculations and measurements of standard spectra. Experimental conditions affecting the response function have been studied and corrections for source scattering and pileup devised. / An anomalous shift in the electron energy calibration caused by the magnetic field has been discovered and explained. / The beta spectrum of ('32)P, ('90)Y, ('28)Al, ('42)K, ('38)Cl and ('88)Rb have been studied. Systematic uncertainties in endpoint, branch intensity and shape factor measurements have been estimated. / A beta spectra analysis program has been written to calculate endpoints, branch intensities and shape factors in a multi-branch spectrum. / The beta spectra of ('141)La, ('142)La, ('139)Ba, ('141)Ba, ('142)Ba, ('138)Cs and ('139)Cs have been studied. Q(,(beta))-values, intensities for all branches and some shape factors have been measured. / The shape factor of the ('20)F beta spectrum has been measured. The value found for the linear coefficient, a = 0.006 (+OR-) .002 (mc('2))('-1), supports the "weak magnetism" predictions of the Conserved Vector Current theory.