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A thin-lens beta-ray spectrometer has been modified for collection of beta-rays at the position of the ring focus. This has increased the gathering power/line width ratio from ∽ 0.12 to ∽0.8. The focusing properties of the instrument have been investigated for various geometries. Using the modified spectrometer, the decay scheme of Sb 125 - Te 125 has been investigated. The primary beta spectrum, photoelectron spectra and beta-gamma coincidence spectra have been measured. From conversion coefficient measurements, the following radiative transition multipolarities were determined (energies in kev): 176(E2+M1), 428(E2+M1), 464(E2), 602(E2+M1) and 638(E2). Five primary beta groups have been identified with end point energies of 626, 450, 307, 246 and 133 kev. Previously unobserved transitions of 76, 143, 219, 355, 540 and 640 kev have been identified. Based on all experimental evidence the following states of Te 125 with spin and parity assignments have been proposed: ground state (S1/2+), 36 kev (d₃/2+), 145 kev (h₁₁/₂-), 321 kev (9/2-), 464 kev (5/2+), 525 kev (11/2- or 9/2-), 540 kev (11/2- or 9/2-), 638 kev (5/2+) and 676 kev (spin and parity undetermined). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The nuclear energy levels of As⁷⁵ have been investigated through the study of the Se⁷⁵ decay scheme. The internal conversion spectrum as well as the photoelectron spectra (using bismuth and lead radiators) were measured with a modified thin lens magnetic spectrometer. A technique was developed for accurate determination of the transmission of the spectrometer in order to obtain the absolute conversion electron transition intensities. The gamma ray intensities were determined from the spectrum measured with a NaI(T1) scintillation spectrometer in conjunction with the results from the photoelectron spectra. From these measurements the absolute conversion coefficients for eight transitions were obtained. In addition coincidence techniques employing a slow- fast coincidence system (resolving time 10⁻⁷ sec) were used to measure gamma-gamma coincidences, conversion electron-gamma coincidences and gamma-gamma directional correlations. A one hundred channel kicksorter was used to facilitate accumulation of the data at the relatively low coincidence counting rates. Multipolarities of the following transitions were determined, (energies in kev), 97(E2); 121(El); 136(El); 199(M1+E2); 265(Ml,-0.12<δ(E2)<+0.07); 279(M1+E2, δ =-0.46 ±0.16); 304(E3) and 401(El). Also detected but for which multipolarities could not be determined was a 66 kev transition and a very weak 572 kev gamma transition. In addition the existence of a 24 kev and a 77 kev transition was inferred from the intensity measurements. An energy level diagram for As⁷⁵ has been constructed with the following energy levels and spin assignments, (energies in kev), 572 (7/2 +), 477 (?), 401 (5/2 +), 304 (9/2 +), 279 (5/2 -), 265 (3/2 -), 199 (1/2 -), 0 (3/2 -). It was concluded that the ground state of Se⁷⁵ has even parity. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Excitation functions and production rates are presented for various Ce and Pr radionuclides formed in the bombardment of 141Pr, natLa and natCe with protons. Extensive measure- ments were performed for 141Pr + p up to 100 MeV and for natLa + p up to 20 MeV. The possibility is investigated to utilize tandem targetry for the production of no-carrier-added 139Ce of high radionuclidic purity, having a Pr target in the higher energy slot followed by a La target in a lower energy slot. 141Pr(p,3n)139mNd!139Pr is investigated as an al- ternative to the direct production route 140Ce(p,2n)139Pr for producing no-carrier-added 139Pr of high radionuclidic purity. The advantages and disadvantages of both production routes are discussed. The simultaneous production of 139Pr and 140Nd using Pr as target is also investigated. Experimental thick-target production rates are presented for Pr ra- dionuclides formed in the bombardment of natCe with protons at incident energies of 20, 26 and 32 MeV. All the experimental excitation functions obtained in this work are compared with theoretical predictions by means of the geometry-dependent hybrid (GDH) model as implemented in the code ALICE-IPPE. The results of this work are also compared with previous literature experimental data, if available.

Alpha-melanotropin (alpha-melanocyte stimulating hormone, α-MSH) exerts its biological action by binding to specific receptors on the outer cell membranes of its target tissues with a high degree of affinity and specificity. Current evidence suggests that this takes place both in vitro and in vivo in both normal and malignant melanocytes. Thus, if it were possible to attach a radioisotope (e.g., ¹²⁵I) to α-MSH, or a suitable analogue, without interfering with the receptor affinity of the hormone, then a radioreceptor assay could be developed which would allow hormone-receptor interaction to be studied in detail. In addition, this radio-labeled melanotropin might be expected to accumulate in melanoma tumors in vivo thus facilitating tumor localization by nuclear imaging methods as has been successfully accomplished for thyroid tumors. The present studies were initiated to develop a radioactive melanotropin with full, or nearly full, biological activity. This labeled melanotropin must be of sufficient specific radioactivity to be suitable as a tracer in a radioreceptor assay and ultimately as a marker for in vivo tumor localization. The studies described herein provide information concerning: chloramine T induced iodination, lactoperoxidase catelyzed iodination, and iodogen induced iodination of α-MSH and certain structural analogues. Radio-labeled derivatives of various melanotropins were prepared using a variety of iodination techniques. Under conditions commonly used for the iodination of other peptides a substantial loss of biological activity of the native hormone (α-MSH) was observed. This loss of hormonal activity was primarily a consequence of oxidation of methinonine and occurred regardless of the oxidant used (chloramine T, lactoperoxidase-hydrogen perioxide, or iodogen). Under similar iodination conditions using 4-norleucine-alpha-melanotropin ([Nle⁴]-α-MSH), satisfactory incorporation of label into the peptide was accomplished without significant loss of biological activity. Data are presented suggesting that this peptide is far superior to α-MSH for use in the preparation of a radioactive melanotropin. Although some success was achieved using [Nle⁴]-α-MSH with all three iodination methods, the simplest and most consistent method involved the use of iodogen followed by purification of the labeled product using high performance liquid chromatography (HPLC). This importance of these studies in the development of a tracer for a radio-receptor assay and for in vivo localization of melanoma tumors is discussed.

A chemical-isotopic equilibrium model was developed for adjustment of radiocarbon ages of groundwater from the arid Tucson basin for dilution of the initial groundwater C-14 activity by the solution of soil calcite having a C-14 of 25 ± 19% modern. Input to the model consisted of the laboratory chemical analyses for Ca⁺⁺, Mg⁺⁺, Na⁺, H₄SiO₄, SO₄⁼, HCO₃⁻, CO₃⁼, NO₃⁻, and pH, and δ C-13 for the total dissolved carbon in the groundwater. Output consisted of the equilibrium chemical composition of the groundwater, the ratio of soil CO₂ derived to total dissolved carbon, Q, and δ C-13 of total dissolved carbon, H₂CO₃, HCO₃⁻, and CO₃⁼, and δ C-13 for the soil CO₂ and calcite that initially dissolved in the surface water as it equilibrated with soil minerals. Radiocarbon age of the groundwater is computed from the equation T = 8270 ln [(Q + (1-Q) A(CaCO₃)/Am] where T is the age in years before A.D. 1950, A(CaCO₃) is the soil calcite activity and Am is the measured activity for the dissolved carbonate in the groundwater, both with respect to modern wood. The validity of the model was tested by comparing the predicted values for δ C-13 (CO₂), δ C-13 (CaCO₃) with measured values for samples from the Tucson basin. δ C-13 (CO 2) calculated = (-12.9 ± 1.9) per mil PDB. δ C-13 (CO2) measured = (-15.1 ± 2.8) per mil PDB. δ C-13 (CaCO3) calculated = (-3.9 ± 1.7) per nil PDB. δ C-13 (CaCO3) measured = (-3.6 ± 1.7) per mil PDB. On the basis of these results, the model adequately describes the natural system and may prove useful in future radiocarbon dating work in desert regions.

Recent years have seen increasing use of atmospheric radionuclides for dating and tracing hydrogeologic processes. Hydrologists often assume that meteoric sources of these nuclides are dominant in ground water and that age-dating methods are limited primarily by analytical detection capability. However, in some cases, subsurface production may also limit the usefulness of these nuclides for dating. Equilibrium radionuclide concentrations are calculated as a function of depth for a variety of rock types. Production mechanisms include fissioning of heavy radionuclides; spallation by cosmic-ray nucleons; capture of neutrons, a-particles, muons and protons; and photonuclear reactions. Calculations indicate that deep subsurface production of ³H, ¹⁴c, ⁸⁵Kr and ⁹⁹Tc is generally below detection but that deep production of ³⁶C1, ³⁹Ar, ⁸¹Kr and ¹²⁹I establishes limits to age-dating of water in most rocks. Parameters for estimating production of ¹⁰Be, ²²Na, ²⁶Al, ³⁷Ar, ³²Si, ⁴¹Ca and ⁷⁹Se are included in appendices. Evidence for in-situ production of ³⁶C1 and ¹²⁹I is presented for two field studies. Concentrations in ground water from the Stripa granite, Sweden, were determined by accelerator mass spectrometry. ¹²⁹I values range from 1,000 to 200,000 atoms/ml, compared to an estimated background concentration in pre-1945 water of 20 atoms/ml. The high levels are attributed to production by spontaneous fission of ²³⁸U in the granite (44 ppm U). ³⁶C1/C1 ratios range from 50-200 x 10 -15 compared to about 40 x 10⁻¹⁵ in meteoric recharge. An increase in ratios with depth has been attributed to production of ³⁶C1 by neutron- capture on ³⁵C1 and is used to set upper limits on the residence time of water in the granite. The validity of using ³⁶C1/C1 ratios as a monitor of deep lithospheric neutron fluxes was tested by measuring the ratios in Cl extracted from Stripa granite. The average ratio, 190 x 10⁻¹⁵, agrees with ratios calculated based on rock chemistry, 190 x 10⁻¹⁵, and on the measured neutron flux, 220 x 10⁻¹⁵. ¹²⁹I and ³⁸C1 were also measured in uranium ores from the Koongarra and Ranger deposits, N.T., Australia. Samples from the oxidized ore zone contain only 6-23% of the ¹²⁹I contents predicted for equilibrium, suggesting preferential loss of ¹²⁹I relative to U during weathering. ³⁶C1 is produced as a result of high neutron fluxes in the ore. Measured ³⁶C1/C1 ratios range from 3 x 10 -12 to 1 x 10⁻¹⁰, corresponding to apparent neutron fluxes of 2 x 10⁵ to 1 x 10⁷/cm²/yr.

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