The e-linac beam that will serve the ARIEL Electron Target East (AETE) has an energy range from 30 MeV to 50 MeV with a power up to 500 kW. The beam electrons are to be converted into photons by means of an electron-to-gamma converter with the purpose of inducing photonuclear reactions in a target to produce exotic isotopes. In the process of conversion, the primary electron beam power deposition in the converter causes a significant increase of the temperature that must be dissipated. The converter performance contributes notably to the overall isotope production and extraction efficiency. This thesis describes the work to optimize and verify the conceptual design of the electron-to-gamma converter through simulations and experimental measurements. / Graduate

Master of Science / Department of Geology / Matthew E. Brueseke / Mid-Miocene epithermal Au-Ag ores of the northern Great Basin USA are related to magmatism associated with the inception of the Yellowstone hotspot. The geochemical chemical connection between these ores and spatially and temporally related volcanism is not well understood, but has been suggested (Kamenov, 2007; Saunders et al., 2015). These Cu- and Pb- isotope studies show that the ore and associated gangue minerals have different sources of Pb, which supports evidence that the metal(loids) originate from a deep magmatic source (Saunders et al., 2008). Cu isotopes as a tool for exploring linkages between ore deposits and related volcanic rocks is a new and evolving field. A suite of mid-Miocene Northern Great Basin (NGB) and Snake River Plain (SRP) volcanic rocks was analyzed by aquaregia leach for their δ⁶⁵Cu compositions. These samples have all been previously characterized and include basalts, trachybasalt, basaltic andesites, and basaltic trachyandesites that are representative of regional flood basalt magmatism and younger basalt eruptions in central Idaho. Included are rocks from the Santa Rosa-Calico volcanic field, NV (e.g., Buckskin-National district); Owyhee Mountains, ID (Silver City District); Midas, NV region, near Jarbidge, NV; and a locality proximal to Steens Mountain, OR. Also included are two Pleistocene basalts from the central Snake River plain unequivocally related to the Yellowstone hotspot volcanism (McKinney Basalt and Basalt of Flat Top Butte), and one Eocene basalt from the Owyhee Mountains that is related to pre-hotspot arc volcanism. International rock standards ranging from ultramafic to intermediate were also analyzed in this study for comparison. Our new δ⁶⁵Cu data greatly expands the range of known Cu isotopic compositions for basalts, with values ranging from -0.84‰ to +2.61‰. These values overlap with the δ⁶⁵Cu of regional ores, further suggesting a link between the source(s) of the ores and the NGB rocks. The range of δ⁶⁵Cu values also overlaps with mantle rock values, suggesting that the Cu isotopic composition may be a signature derived from the mantle source. Fractionation mechanisms that cause such a broad range in Cu isotopes are still unclear but liquid-vapor transitions and mantle metasomatism are being explored. Furthermore, δ⁶⁵Cu values of international rock standards reported in this study did not agree with previously reported data (Archer and Vance, 2004; Bigalke et al., 2010; Moeller et al., 2012; Liu et al., 2014, 2015) suggesting that aquaregia leach may not be a preferable technique when analyzing volcanic rocks.

No description available.

A combined experimental and computational study on the reversible ortho-metalation exhibited by the triosmium cluster Os3(CO)10(dppm) (dppm = 1,1-bis(diphenylphosphino)methane is reported. The conversion of nonacarbonyl cluster HOs3(CO)9[-PhP(C6H4)CH2PPh2] to Os3(CO)10(dppm) is independent of added CO and exhibits a significant inverse equilibrium isotope effect (EIE). Reductive coupling of the C-H bond in HOs3(CO)9[-PhP(C6H4)CH2PPh2] leads to the formation of agostic C-H and two distinct aryl-π species prior to the rate-limiting formation of the unsaturated cluster Os3(CO)9(dppm). Heating the unsaturated dimer H2Re2(CO)8 with Cp*Rh(CO)2 (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene) at elevated temperature affords the new trimetallic clusters H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6, and the spiked-triangular cluster HRhRe3Cp*(CO)14. H2Re2(CO)8 reacts with Cp*2Rh2(CO)2 under identical conditions to furnish H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6 as the principal products, in addition to the tetrahedral cluster H2Rh2Re2Cp*2(CO)8. H2RhRe2Cp*(CO)9 undergoes facile fragmentation in the presence of halogenated solvents and the thiols RSH (where R = H, C6H4Me-p) to afford the structurally characterized products Cp*Rh(-Cl)3Re(CO)3, S2Rh3Cp*(CO)4, Cp*Rh(-Cl)(-SC6H4Me-p)2Re(CO)3, and Cp*Rh(-SC6H4Me-p)3Re(CO)3. The new hydrazido-substituted compounds TaCl(NMe2)3[N(TMS)NMe2] (TMS = tetramethylsilyl) and Ta(NMe2)4[N(TMS)NMe2] have been synthesized and their structures established by X-ray crystallography. The latter product represents the first structurally characterized octahedral tantalum(V) complex containing a single hydrazido(I) ligand in an all-nitrogen coordinated environment about the metal center. The fluxional properties of the amido and hydrazido ligands in these new compounds have been established by VT 1H NMR spectroscopy (VT = variable temperature). Preliminary data using Ta(NMe2)4[N(TMS)NMe2] as an ALD (ALD = atomic layer deposition) precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.

>Magister Scientiae - MSc / It is well known, that there is a severe lack of information available pertaining to neutron rich nuclei, specifically of those nuclei with mass numbers ≥ 60. These neutron rich nuclei are not easy to access in current experimental facilities or be produced with sufficient yield to allow for it to be studied. In order to expand our understanding of nuclear physics by studying the properties and characteristics of these nuclei, the development of new facilities producing Radioactive-ion Beams (RIBs) is required. The applications for RIBs are wide, allowing for deeper investigations into the properties of nuclei, their interactions and the manner in which they were formed in the early universe. Additionally, there are various interdisciplinary fields such as medicine, biology and material science in which RIBs can be utilized as a driving mechanism for new research and technological innovation. The iThemba Laboratory for Accelerator Based Sciences (iThemba LABS), South Africa, has proposed a new facility for the production and acceleration of radioactive-ion beams (RIBs). The RIB Project is to be developed in sequential phases and would produce a range of neutron-rich isotopes for low-energy materials science and nuclear physics research. Of specific interest, is the production of the Helium-6 isotope (6He), for its potential applications in various areas of nuclear physics research. The aim of this research work was to design, model and optimise a RIB production target capable of producing high intensity 6He beams, guided by the characteristics of the primary proton beam available for use at iThemba LABS. This research work/design study is however limited, due to the absence of experimentally measured and verified 6He cross section data for proton induced reactions on the proposed target materials (Graphite and Boron Carbide). However, best-estimate approaches were adopted through the use of validated computer codes. Additionally, all 6He yield results are presented as in-target yields, as this study did not cover the diffusion (isotope release) efficiency of the target systems in question. Three RIB production targets types were investigated using Graphite, Boron Carbide and Beryllium Oxide as potential target materials. Following numerous optimisation processes, a Boron Carbide RIB target was converged upon, proving to be suitable for the production of high intensity 6He beams at iThemba LABS, by meeting the material thermal and mechanical limiting criteria for operation. This target system was found to produce an in-target 6He yield rate of 2 ~ 3 x 1011 6He/s, considered sufficient for experimental application at iThemba LABS.

This Ph.D. Thesis is focused on the effect of submerged vegetation on the structure of lake ecosystem and trophic relationships among fishes. Succession of submerged vegetation is a dynamic process and the vegetation community may change dramatically even during a year. Many environmental factors have impact on the succession of submerged vegetation and consequently the presence of the vegetation has substantial impact on the aquatic ecosystem. Nutrient level (mainly nitrogen and phosphorus) plays a key role in the succession of freshwater ecosystems. Further, herbivory significantly influences species composition and biomass of macrophytes and macroalgae. Herbivory of fish is a foraging strategy that is dependent on temperature. Foraging preferences of fish may suppress the palatable species. The rate of herbivory affects plant growth patterns and thus inpalatable species may be advantaged in the competition among plants. In aquatic ecosystems, herbivory is often performed by omnivorous species. The diet preferences of omnivorous fish differ among aquatic ecosystems and submerged vegetation can shape their trophic niches substantially.

Individuals within fish populations differ in many traits, such as sex, life-history, habitat residence, diet, and morphology. Such trait differences among individuals (i.e. intra-population variation) may be greater than the differences among populations (i.e. inter-population variation). My dissertation examines intra-population variation, with a focus on trophic relationships and morphology; as well as how variation in these attributes may reflect differences in bioaccumulation of contaminants. The second chapter of my dissertation examines the influence of spatial-temporal variation on the trophic structures of round goby (Neogobius melanstomus) and two age classes of yellow perch (Perca flavescens) within Saginaw Bay, Lake Huron. Using stable isotope ratios (δ13C, δ15N, δ2H, δ18O) and stomach contents as trophic indicators, I examined variation of diets. I found that spatial variation had a greater impact on diet indicators than both annual and seasonal variation. This spatial variation could represent a form of compartmentalization within the community of fish residing in Saginaw Bay, and could provide stability to the community. Chapter three of my dissertation examines intra-population variation in yellow perch morphology through a series of mesocosm experiments. My first mesocosm study determined that yellow perch could be experimentally manipulated to display divergent morphologies using simulated habitats, specifically pelagic and littoral habitats. Following this experiment, I focused on specific environmental drivers (structure, prey resources, and predation risk) as possible influences on yellow perch morphology. Within experimental pools, I exposed yellow perch to one of four treatments (an open pool, a structured pool, pools with chironomid prey resources and pools with a perceived, olfactory, predation risk) in the summer of 2015. Following exposure to these treatments I examined the morphological changes in yellow perch in magnitude and direction. I observed that while each treatment induced some difference in morphology, the open and structured treatments had the greatest magnitude of difference. I repeated the open and structure treatments during the following summer (2016). Again, I found that structure and open morphologies could be induced by my mesocosm treatments, but also observed that shapes differed from the previous year’s structure and open treatments. Finally, my fourth chapter examined how variation in trophic niches and morphology may reflect variation in contaminant concentration of fish in their natural environment. In this chapter, I extended my work with yellow perch to also include black crappie (Pomoxis nigromaculatus) and examined fish from 5 northern Indiana glacial lakes. Using model inference techniques, I found that variation in mercury was closely associated with not only fish total length, but also stable isotopes (δ13C and δ15N) and morphology. Interestingly, morphology-related variables of both species were strong predictors of mercury concentration in fish, following total length. Together, the chapters within my dissertation highlight the importance of considering intra-population variation, in which local factors such as habitat conditions and prey availability can influence individual variation in trophic structuring and morphology. These in turn may reflect other attributes of interest, such as the accumulation of contaminants.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements of the degree of Master of Science in Geology Johannesburg, 1998 / This study determines the potential of prerncting pollution to ground water by sanitary landfills. The tracing capabilities of both stable and radioactive environmental isotopes are also evaluated. Four landfills were selected, the Linbro Park and Waterval sites in Johannesburg, and the Bloemfontein northern and southern landfill sites. The sites all differ in geological environment, size. age and physiographic setting. [Abbreviated Abstract. Open document to view full version] / MT2017

A dissertation submitted to the Faculty of Science, University of Witwatersrand, in fulfilment of the requirements for the degree of Masters of Science Johannesburg, 2012. / Amplified loads of sulfate and nitrate have caused increased stress on soil systems in many areas of the world, as both are dominant components of acid rain. This is a critical environmental stress due to the damage caused to soil, water quality and ecosystem functioning. Issues concerning the rising emissions of these elements from local industries have begun to attract increasing attention in South Africa, as the rates of deposition in the Mpumalanga Highveld region alone is comparable to those experienced in First World countries. This study sought to investigate the use of natural stable isotopes of sulfur and nitrogen to identify the process transformations that these species undergo in environmental cycles. Total δ34S, δ15N and δ13C isotope signature of soils in the Mpumalanga region were combined with total elemental concentrations to determine the effect of deposition on the soil system. Soil samples from two soil depths (0 – 10 cm and 20 – 40 cm) were taken along a distance gradient from an identified pollution source, the Majuba power station. Long-term air quality data from the study area were also obtained from Eskom’s air quality monitoring stations, as well as sulfur and nitrogen deposition data from selected literature. Elemental concentrations decreased with soil depth as expected, while sites located approximately 25 km downwind of the power station were seen to contain higher concentrations of both soil sulfur and nitrogen. The mean per site soil sulfur concentration across all depths ranged from 0.009 % to 0.048 %, while the mean per site nitrogen concentration across all depths ranged from 0.056 % to 0.346 %. The mean soil carbon concentration in the top-soils ranged from 0.97 % to 7.93 %, and decreased in the sub-soils to 0.490 % to 3.270 %.The mean δ34S value for the top-soils was found to be 8.28 ‰ and increased to 10.78 ‰ in the sub-soils. Soil δ15N also increased with soil depth from 6.55 ‰ to 8.28 ‰. Soil δ13C values were seen to increase from -12.83 ‰ in the top-soils to -11.90 ‰ in the sub-soils. Lighter δ34S values at the surface may be due to anthropogenic deposition. The positive δ34S shift was attributed to a two-source mixing model (atmospheric deposition and bedrock) and isotopic fractionation processes that occur within the soil profile. The δ15N values of the top-soil were higher than what is expected if all nitrogen was derived from atmospheric nitrogen gas fixation. The increase in δ15N with depth suggested that isotope fractionation occurred during nitrogen export due to the faster reaction rate of 14N compared to 15N. The soil δ13C values indicated a typical C4 grassland system. New carbon at the top-soil depths was enriched in 13C due to the slower decay of 13C-depleted lignin; whereas in the sub-soils microbial recycling of carbon dominates and explained the higher 13C content of the older carbon. The conceptual framework presented for this project involves simultaneous processes of deposition and export in the soil system. This was particularly true for sulfur, where sites with lower isotope values had lower soil sulfur concentrations and vice versa. This indicates that high levels of deposition correspond to high net export. The sulfur and nitrogen isotopic signatures could not be used to as a direct means of source identification; however, the effectiveness of isotopes in elucidating transfer of these nutrients in the soil system was illustrated.

Faculty of Science; School of Geography, Archaelogy and Environmental Studies; PhD Thesis / This thesis investigates agropastoral production and ecological conditions under which complex socio-political systems in the Shashe/Limpopo River Basin, southern Africa, periodically expanded and declined between ~AD 900 and 1700. Environmental reconstruction for this period, derived from multi-stable isotope analysis of modern and archaeological fauna from the area, demonstrate that agropastoral settlement and changes in their social, economic and political complexity were less driven by climate than previously had been assumed. Rather, at a relatively short-term climatic scale, these cultural events took place even as precipitation and temperature appeared to have fluctuated above and below the modern seasonal mean of ~350mm and ~22oC, conditions presently considered to be marginal for agropastoral production. Alternative to a climate driven model for settlement, ethnographies of traditional southern African agropastoral systems provide a comparative basis for understanding the range of environmental and social parameters that past agropastoralists in the Shashe/Limpopo River Basin may have employed to sustain population growth and intensify socio-political complexity in the face of short-and long-term climatic variability. Over a long-term climatic scale, the δ15N and δ18O values from Bos taurus and Ovis/Capra indicate that the initial settlement by Zhizo agropastoralists people, between AD 900 and 1010, took place under semi-arid conditions that were similar to, or only marginally wetter, than the present. This thesis suggests that the Zhizo settlement and their ‘capital’ site of Schroda were motivated by broader cultural factors, such as trade networks, and not solely by climate conducive for agriculture. As documented ethnographically, crops and livestock herds could have been sustained by taking advantage of various geographical features of the river basin, such as planting near outcrops where dammed water keep soils moist even in dry periods and using browse and crop fodder to offset diminished grazing lands. Results for sites dating between AD 1010 to 1415, support previous interpretations that the Leopard’s Kopje A and B cultural period ‘capitals’ of K2 and Mapungubwe, respectively, rose to prominence under a trend towards increased available moisture. The additional moisture would have facilitated the greater floodplain settlement recorded between AD 1010 and 129, which was most likely a response to increased population pressures of the capitals and the need to extend cultivated lands. This spatial shift was accompanied by an apparent greater management of livestock. The preliminary 87Sr/86Sr data, together with intra-annual δ18O and δ13C values, from B. taurus and Ovis/Capra indicates a geographical expansion of herd management took place with the transition from K2 to Mapungubwe. This thesis proposes that to sustain population and socio-political growth in the face of short-and long-term climatic variability, livestock management would need to be politically coordinated. Maintaining large-scale herds outside the river basin would have allowed for expansion of crop production onto previous river basin pasturelands, while extending territories or networks. Further, the δ15N and δ18O data indicates that the period of increased available moisture extended beyond the abandonment of Mapungubwe at AD 1290. Previous assumptions that link this event to the negative agricultural impact of a cool dry trend starting at ~AD 1300, as extrapolated from sub-continental scale climatic sequence, must be re-assessed. The isotopic data from Moloko/Khami cultural period sites suggest that drier conditions did not develop in the area until after ~AD 1450. Their initial settlement in the area during this drier period needs to be re-considered, as does the entire sequence from ~AD 900 onward, in terms of agropastoral production strategies within shifting natural, economic and political environments.