Department of Physics and Astronomy

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Black Holes 'NSinc: The SA discovery that’s got astronomers in a spin

A deep scan of the sky in radio waves revealed something completely unexpected to South African astronomers: that somehow, and for some unexplained reason, supermassive black holes in one region of space are all releasing radio waves in the same direction. Could this be a vital clue in understanding how the universe was formed?

Astronomers Perplexed By Rare Alignment Of Supermassive Black Holes (Youtube video)

Centre For RadioCosmology: Astronomy For The 21st Century

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Inleiding tot die eksperimentele Sielkunde
(University of the Western Cape, 1948) Schlebusch, B. J.; Van Rensburg, J. A. J.
Elke skolier wat rue tevrede is om dit op skool slegs met lepels in te kry nie, het seker al gewonder hoe kennis oorspronklik verkry word. In daardie stadium is ons gewoonlik nog tevrede om die feite wat die onderwyser aan ons voorlê, of wat ons in die boeke gelees het, op gesag aan te neem. Maar selfs dan toets ons dikwels daardie gesag deur gewone en terloopse waarnemings. Byvoorbeeld: in die fisika leer ons dat as ons 'n groot en 'n klein klippie gelyktydig van enige hoogte laat val, hulle ook gelyktydig op die aarde sal beland as daar nie met die een klip intussen iets gebeur het wat nie met die ander klip gebeur het nie: met ander woorde as aIle faktore gelyk gebly het. Toe ons van hierdie gelyk-vallende klippies gehoor het, het party van ons op 'n dubbelverdieping gebou, of selfs op die dak van die buitegebou, opgeklim en die twee klippies self laat val om na te gaan of dit werklik so was. En hiermee het ons 'n eenvoudige eksperiment uitgevoer om te toefs of die hennis wat ons geleer het wel reg was. Dit was 'n eenvoudige eksperiment omdat die invloed van die lugdruk, en van die wind wat waai en 'n groter uitwerking op die groot klip het as op die klein klippie, buite rekening gehou is by die waarneming. Ons het ook net van ons oë gebruik gemaak om te kyk of die twee klippe gelyktydig op die aarde beland. Maar as ons middels kon aangewend het om die invloed van die genoemde twee faktore te bepaal, sou dit 'n meer presiese eksperiment gewees het en nie 'n terloopse waarneming nie. Sulke presiese eksperimente word in die laboratorium uitgevoer met die doelom betroubare kennis te kry. Die soort wetenskaplike kennis wat ons op skool leer, is reeds in die verlede deur navorsers vasgestel, en hulle bevindings is nou beskikbaar vir ons in teksboeke. Hulle eksperimente was bedoel om op nuwe kennis uit te kom. Maar die student wat sy verstand gebruik is nie noodwendig tevrede met gesag nie; hy wil self graag eksperimente maak om te sien of wat die gesag beweer werklik so is. Sy eksperimente is bedoel om eerstens te toets of die ander navorsers se resultate reg is, en tweedens 0111 hom oefening te gee met die uitvoering van eksperimente. Navorsers werk op wetenskaplike manier om nuwe kennis te verkry. Dit word vertel dat Newton S)' idee van die aantrekkingskrag van die aarde gekry het toe hy 'n appel sien val het, en dat Archimedes die idee van sy wet: dat voorwerpe in water van hulle gewig verloor, en dat die gewig wat daardie voorwerpe verloor gelykstaan aan die gewig van die volume water wat deur die voorwerpe verplaas word, gekry het terwyl hy besig was om te bad. Waarheid is dat albei allank besig was om oor hulle probleme na te dink en na te soek, en dat toe Newton die appel sien val het en Archimedes die gedagte in die. bad gekry het, dit feite was wat by vorige kennis aangesluit het. Hulle was egter nie daarmee alleen tevrede nie; daarna het albei die gedagte gaan toets .met wetenskaplike proefnemings om op kennis uit te kom. Die proefnemings en wetenskaplike navorsing kan jare en jare se harde werk vereis het. Om die eerste atoombom te laat ontplof het tientalle wetenskaplikes en duisende geskoolde assistente en werksmense jare se werk gekos. So het dit ook baie jare geverg om vas te stel dat mense wat siek word nie getoor is nie maar dat, byvoorbeeld, kieme 'n groot rol kan speel byeen of ander siekteverskynsel; en dit weer het ons aan die wetenskaplike navorsingsmetodes van 'n Pasteur te danke. Die verslag valt wetenshaplilu: navorsers se werk is nou ons wetenskaplike literatuur. Hierdie mense wat 'n eksperiment vir die eerste keer gemaak het, het dit nie gedoen om te toets of ander mense se feite korrek is nie, maar om uit te kom op oorspronklike feite van hul eie. In die Sielkunde is die basis vir die metodes van ondersoek dieselfde as vir ander wetenskappe. Daar is die noodsaaklikheid om deur middel van wetenskaplike proefneming op nuwe kennis uit te kom. Om dit te kan doen moet 'n mens eers leer hoe om 'n proefneming in te rig en moet jy voldoende oefening kry met proefnemings. As studente is dit vir ons 'n vereiste om die verskillende verskynsels self te kan ondersoek en later miskien self op nuwe kennis uit te kom en, wie weet, self een of ander oorspronklike bydrae te maak. Maar dan moet ons weet hoe om 'n eksperiment of ondersoek uit te voer. Om dit geleerd te stel: Ons moet die objektiewe metodes van 'n wetenskaplike eksperiment beheer; ons moet weet hoe om 'n proefneming in te rig.
(p.n.) Reactions on 59co in the intermediate energy range
(University of the Western Cape, 1992) Bester, P.J; van Heerden, I.J.
Detailed theoretical investigations [Chi80,Mos82,Kle85] of (p,n) and (p,p') data indicate that the reaction mechanisms operative at intermediate energies and for energy losses up to several tens of MeV are predominantly single-step in nature. In these direct reactions, only a few nucleons take part in the reaction, with the remaining nucleons of the target serving as passive spectators. Many excited states of the product nucleus can be reached in these reactions.
Cross-sectional transmission electron microscopy of nickel silicide formation
(University of the Western Cape, 1993) Julies, Basil Allen; Knoesen, D; Pretorius, R
Silicides play a significant role in modern device technology. The operation of electronic devices heavily relies on the specific properties of metal-semiconductor interfaces. Although semiconductor technology has proven very successful in utilizing the properties of materials the knowledge on formation, structure and electrical behaviour of interfaces is still far from complete. In this study an investigation into the Ni-Si binary system was made. Several techniques namely Rutherford Backscattering Spectroscopy, Transmission Electron Microscopy, Scanning Electron Microscopy, Auger Emission Spectroscopy and X-ray Diffraction were employed in the characterization of nickel thin films on silicon and the respective silicides which were formed. Special attention was given to the phase transition from NiSi to NiSi2. First phase formation, namely Ni2Si, was investigated at a vacuum furnace temperature of 290°C. This phase was found to be polycrystalline and grew in layers of uniform thickness with sharp Si-silicide and Ni-silicide interfaces. Growth continued until all the Ni-metal was consumed. Second phase formation (NiSi) was observed at 330°C only after the Ni2Si has grown to its full thickness. This polycrystalline phase also grows in layers. These layers however, are not of uniform thickness, the interfaces between the silicide and silicon substrate therefore being less regular. It was found that NiSi grains could assume one of two crystal structures, orthorhombic or a FeSi cubic structure. Generally it seems as if NiSi initially crystallizes into an orthorhombic crystal structure, before undergoing an allotropic transformation to the FeSi cubic structure. Micro-diffraction was used to characterize individual grains. Final phase formation (NiSi2) was mainly examined at 750°C. A scanning electron microscopy investigation showed that after 5 minutes of annealing islands of NiSi2 was observed in a NiSi matrix. With longer annealing times these islands grew laterally and eventually joined up with others. Cross-sectional transmission electron microscopy very firmly confirms the presence of NiSi2 surrounded by NiSi. Rutherford backscattering, X-Ray diffraction and Auger electron spectroscopy complement these results. Scanning electron microscopy shows that after the coalescence of individual NiSi2 islands, holes appear on the grain boundaries. These holes probably result from an accumulation of vacancies on the grain boundaries during NiSi2 formation which occurs via Ni diffusion in NiSi into the underlying silicon. As the NiSi2 phase continues to grow these holes increase in size and later take on the same crystal structure as the surrounding cubic NiSi2 grains. Although the reaction: NiSi + Si => NiSi2 is thermodynamically favourable to occur at 750°C, it was found that even after 15 minutes of annealing at 750°C, some grains were still NiSi while many others had switched to NiSi2. Identification was once again done by micro diffraction. This means that there is more than just the thermodynamic aspect involved in deciding when NiSi should transform to NiSi2. A model has therefore been proposed in which the major factors in determining the time lapse for transformation to take place are presented. This model generally presents an atomistic approach which centres around the degree of Ni diffusion across the grain boundary of two individual grains. Observations also suggests that NiSi2 results from NiSi by a diffusion process although nucleation can take place at random. This model must not be seen as contradictory to models proposed in the literature which only allow for non-uniform growth at the Si-NiSi, interface, but must rather be seen as complementing it by allowing for diffusion processes as well.
Pre-equilibrium cross section calculations with a realistic effective nucleon-nucleon interaction
(University of the Western Cape, 1995) Karriem, Zainuddin; Lindsay, Robert
The principle aim of this work is to improve the way in which pre-equilibrium double differential cross-sections are currently calculated [1, 2, 3, 4]. The theoretical basis for these calculations is the Multistep Direct Theory by Feshbach, Kerman and Koonin (FKK theory) [5]. This theory leads to the simplification of multistep reactions as a folding of single-step reactions through the implementation of the Distorted Wave Born Approximation (DWBA). The pre-equilibrium cross-sections are subsequently calculated with a multistep direct code.
The determination of excitation functions for natRb+p up to 100 MeV with an emphasis on the production of 82Sr
(UWC, 2000) Buthelezi, E.Z; Green, A; Nortier, F.M
The radioisotope strontiuur-S2 (T172= 25.55 days) decays to short-lived t"Rb 1T,, = 76 seconds) by l00o/o electron caphue @C). The short-lived t'*Rb decays by g5.SYopositron-ernissiou p* and 4.5%oEC to stable'2Kr. Rubidiurn-82g is used in Positron Enr.ission Tonrography (PET) applications, including studies of myocardial infarction, kidney tissue, and brain blood florv. In the present study the excitation fi,rnctions for the production of 82Sr, other radio-strontiums, and radio-contaminants produced in the proton bonrbardrnenl of ""'Rb rvere measured by ureans of the stacked-foil teclutique
The influence of maternal nicotine exposure on neonatal rat trachea development and alveoli status
(University of the Western Cape, 2000) Vergotine, Zelda; Maritz, G. S.
The aim of this study was to determine the effect of maternal nicotine exposure on the status of the rat tracheal development as well as the rat lung of 7 to 42 day old offspring. Wistar dams were injected subcutaneously, using a dosage of 1 mg nicotine/kg body mass/day, and treatment commenced 7 days after conception. The morphological and morphometric data were used to evaluate any damage or change in the structure of the trachea and lungs due to maternal nicotine exposure. Three techniques were used namely, light microscopy, scanning electron microscopy and transmission electron microscopy. Both morphological status and morphometric data were obtained from the sample animals.
A case study of university students' experiences of introductory physics drawn from their approaches to problem solving
(University of the Western Cape, 2001) Alant, Busisiwe Precious; Linder, Cendric; Marshall, Delia
This thesis explores the experience of leaming physics through a particular medium: problem-solving, which is seen by many educators as the primary medium in which physics is learnt at university. Situating itself within two theoretical perspectives: phenomenography and actor-network theory, the dissertation explores the variation in the ways of experiencing introductory physics leaming through problem-solving. phenomenography, which is the main theoretical framework, places emphasis on the variation of experience of phenomenon at a supra-individual level. Leaming is regarded as relational, which means that the act of leaming is apprehended (in terms of how the learning is done as well as what is leant) in the relation between the leamer and the phenomenon. Rather than regard the content of physics learning as the phenomenon, the study proposes the process of learning physics through problem, solving as the phenomenon under investigation. The thesis draws on insights from actor-network theory, particularly with regard to the spatiality of leaming. Learning is seen as a function of enrolment. Fifteen students were interviewed on introductory physics problems encountered in four end-of-module tests. The data were analyzed on the basis of strategy - conceived as "moments,' of problem-solving, as well as the factors (intentional and contextual) that could be seen to influence the strategy adopted. Two qualitatively distinct problem-solving strategies were identified, derived from the relative presence of reflective awareness. Further, factors influencing the strategies were identified and found to be indicative of two qualitatively distinct ways in which the students focused on the problems - either on problem content (the physics concepts) or on problem requirement (the formal requirements of the task within the test setting). These findings are seen to constitute the structural aspect of the students' experience of physics learning through problem solving. With regard to the referential aspect of the experience, the study derives two overall meanings that the students attached to their experience of physics learning through problem-solving, namely physics leaming as "reconstituting understanding', and physics learning as, confirming convention". It is argued that the variations identified in the strategies employed by the students, in the ways they focus on problems, in their perception of the problem-solving settings, in the meanings they attach to physics learning through problem-solving - call for a framework of learning that takes account of spatiotemporal intricacy. The notion of conceptual understanding in the learning of physics should be informed by the specific demands of the medium of problem-solving through which physics is learnt at undergraduate level
Antimicrobial activity of South African red algal secondary metabolites
(UWC, 2001) Cameron D; Keats, DW; Cyster, LF; Leng, H; Green, I
Infectious diseases, for example, measles, scarlet fever, malaria, tuberculosis, and cholera have claimed many lives. These infections are caused by pathogenic viruses, bacteria, or fungi that invade the body's tissues and multiply. According to the Online Medical Dictionary (2000), the multiplication may be clinically barely visible or result in local cellular injury because of competitive metabolism, toxins, intracellular replication, or antigen-antibody response. An infection may remain localized, sub-clinical, and temporary if the body's defensive mechanisms are effective or it could persist, spread, and become an acute, sub-acute, or chronic clinical infection or disease state.
Calibration of germanium detectors for applications of radiometric methods in South Africa.
(University of the Western Cape, 2001) Maleka, P.P; Lindsay, R.; de Meijer, R. I.
AII materials that are radioactive emit characteristic gamma-radiation. Natural radioactivity can be used in heavy minerals exploration and processing, as well as in understanding sediment transport. processes in coastal zones [Dem97][Dem98]. Differences in radionuclide concentrations between minerals, allows the mineral species to be identified and quantified by the activity concentrations of a011, 23216 and 238U using a technique called radiometric fingerprinting [Dem97]. A" important tool to determine sediment transport rates along the coastline is by the MEDUSA technology developed and tested at the Kernfysisch Versneller Instituut (KVI) [Dem98]. The data from the MEDUSA (Multi-Element Detector system for IJnderwater Sediment Activity) system needs to be calibrated first in the laboratory before field measurements can be converted to useful data. The National Accelerator Centre (NAC) is setting up a radiometric laboratory to do this by means of a high-resolution germanium detector used under low-background conditions and constant geometry.
Study of the use of Electret Ion chambers as radom dosimeters in South Africa
(University of the Western Cape, 2002) Vuza, Hurnphrey Monwabisi; Lindsay, R
Radon is a naturally occuring radioactive gas which has been shown to be a major contribution to background dose. The underground mines in South Africa present a major occupational hazard. A need for cheap personal monitoring has been identified. In this thesis, commercially available electret ion chambers (EICs) are studied, with a view to use them as personal monitors. These detectors were developed to measure radon activity concentrations in houses. Their use in the harsh underground mining environments has shown some complications such as water entering the detectors and their response time to a rapid change in radon concentration has been questioned. Several measurements are discussed in this thesis relevant to solve these problems. Firstly, the EIC's are checked for accuracy in the laboratory using a radon source, as well as the radon chamber at the CSIR in Pretoria. Comparisons with alpha track detectors are also carried out.
Promoting physics and development in Africa
(American Institute of Physics, 2004) Zingu, Edmund
To excel in physics research in Africa is to conquer Mount Everest without the aid of additional oxygen. In a continent that lacks the infrastructure of research laboratories, technical support, and so forth, relatively few physicists have managed to perform at levels competitive with the best in the world. Are the challenges of physicists in Africa any different from those facing physicists elsewhere? Physicists everywhere have to convince their governments, businesses, and the public that investment in physics is beneficial and will lead to economic development and an enhanced quality of life.
Modelling and measurement of radon diffusion through soil for application on mine tailings dam
(University of the Western Cape, 2004) Speelman, Wilcot John; Lindsay, R.; Dept. of Physics; Faculty of Science
Radon has been identified as an important factor that could result in a health hazard by studies all around the world. The health risks can be minimised by preventive measures where radon is highly concentrated as in some mines and homes. Measuring and modelling the radon concentrations in the mine dump soil, can help to deduce the radon flux to identify the problem areas for rehabilitation especially in the cases of gold and uranium mine tailings. Rehabilitation in those cases usually consists of a multilayer cover of solids like crushed rock or clay. A passive method incorporating electret technology was used in this study to determine the radon emanation coefficient of the soil. This investigation also describes the modelling of a depth profile with respect to the radon activity concentration to understand from how deep radon might be migrating, as well as the effect of different diffusion lengths.
Determination of natural radioactivity concentrations in soil: a comparative study of Windows and Full Spectrum Analysis
(University of the Western Cape, 2004) Maphoto, Katse Piet; Lindsay, R.; Newman, R.T.; Dept. of Physics; Faculty of Science
In this study, two methods of analysing activity concentrations of natural radionuclides (U, Th and K) in soil are critically compared. These are the Window Analysis (WA) and Full Spectrum Analysis (FSA). In the usual WA method, the activity concentrations are determined from the net counts of the windows set around individual γ-ray peaks associated with the decay of U, Th and K. In the FSA method, the full energy spectrum is considered and the measured spectrum is described as the sum of the three standard spectra (associated with U, Th and K, respectively), each multiplied by an unknown concentration. The concentrations are determined from the FSA and correspond to the activity concentrations of U, Th and K in the soil. The standard spectra derived from separate calibration measurements using the HPGe detector, represents the response of the HPGe to a Marinelli sample beaker containing an activity concentration of 1 Bq/kg.
Modelling and measurement of radon diffusion through soil application on mine tailings dams.
(University of Western Cape, 2004) Speelman, Wilcot John; Lindsay, Robert
Radon (222Rn) has been identified as an important factor that could result in a health hazard by studies all around the world. The health risks can be minimised by preventive measures where radon is highly concentrated as in some mines and homes. A study in the diffusion of the inert gas, will give us a better understanding of its possible pathways through soil into the air surrounding mine dumps where the radon releases can become hazardous. Measuring and modelling the radon concentrations in the mine dump soil, can help to deduce the radon flux to identify the problem areas for rehabilitation especially in the cases of gold and uranium mine tailings.
A study of hydrogenated nanocrystalline silicon thin films deposited by hot-wire chemical vapour deposition (HWCVD)
(University of the Western Cape, 2005) Halindintwali, Sylvain; Knoesen, Dirk; Dept. of Physics; Faculty of Science
In this thesis, intrinsic hydrogenated nanocrystalline silicon thin films for solar cells application have been deposited by means of the hot – wire chemical vapour deposition (HWCVD) technique and have been characterised for their performance. It is noticed that hydrogenated nanocrystalline silicon is similar in some aspects (mainly optical) to its counterpart amorphous silicon actually used as the intrinsic layer in the photovoltaic industry. Substantial differences between the two materials have been found however in their respective structural and electronic properties. We show that hydrogenated nanocrystalline silicon retains good absorption coefficients known for amorphous silicon in the visible region. The order improvement and a reduced content of the bonded hydrogen in the films are linked to their good stability. We argue that provided a moderate hydrogen dilution ratio in the monosilane gas and efficient process pressure in the deposition chamber, intrinsic hydrogenated nanocrystalline silicon with photosensitivity better than 102 and most importantly resistant to the Staebler Wronski effect (SWE) can be produced. This work explores the optical, structural and electronic properties of this promising material whose study – samples have been exclusively produced in the HWCVD reactors based in the Solar Cells laboratory of the Physics department at the University of the Western Cape.
Aluminium induced crystallization of hydrogenated amorphous silicon thin films
(University of the Western Cape, 2005) Kotsedi, Lebogang; Knoesen, Dirk; Madjoe, Reginalt
This study was carried out to crystallize hydrogenated amorphous silicon (a-Si:H) thin films using the aluminium induced crystallization (AIC) technique. This was done to investigate whether is there any lateral crystallization of the a-Si:H thin film away from the aluminium covered surface of the film. The hot wire chemical vapour deposition system (HWCVD) was used to deposit hydrogenated amorphous silicon thin films (a-Si:H) on Corning glass 7059 substrates. The substrate temperature was kept at 300oC while the filament temperature was l600oC during the deposition. The aluminium top layer was deposited at room temperature using the electron beam evaporator. The aluminium deposited, only partially covered the sample, this was done to investigate whether lateral crystallization of the uncovered part will take place. Samples were then annealed at 450oC for times ranging from 30 to 150 minutes in incremental steps of 30 minutes. A temperature series of annealings at l00oC, 150oC, 200oC,300"C and 350oC for 60 minutes were also performed. Energy Dispersive Spectroscopy (EDS) was used for elemental identification after annealing. Rutherford Backscattering Spectrometry was used for the depth profiling of the diffused species. X-ray diffraction (XRD) technique was used for crystallization studies on the aluminium covered side, transmission electron microscopy (TEM) was used to study lateral crystallization and diffraction patterns of crystallized part were taken using selected area diffraction (SAD).
Determination of the photopeak detection efficiency of a HPGe detector, for volume sources, via Monte Carlo simulations
(University of the Western Cape, 2005) Damon, Raphael Wesley; Lindsay, R.; Newman, R.T.; Dept. of Physics; Faculty of Science
The Environmental Radioactivity Laboratory (ERL) at iThemba LABS undertakes experimental work using a high purity germanium (HPGe) detector for laboratory measurements. In this study the Monte Carlo transport code, MCNPX, which is a general-purpose Monte Carlo N − Particle code that extends the capabilities of the MCNP code, developed at the Los Alamos National Laboratory in New Mexico, was used. The study considers how various parameters such as (1) coincidence summing, (2) volume, (3) atomic number (Z) and (4) density, affects the absolute photopeak efficiency of the ERL’s HPGe detector in a close geometry (Marinelli beaker) for soil, sand, KCl and liquid samples. The results from these simulations are presented here, together with an intercomparison exercise of two MC codes (MCNPX and a C++ program developed for this study) that determine the energy deposition of a point source in germanium spheres of radii 1 cm and 5 cm. A sensitivity analysis on the effect of the detector dimensions (dead layer and core of detector crystal) on the photopeak detection efficiency in a liquid sample and the effect of moisture content on the photopeak detection efficiency in sand and soil samples, was also carried out. This study has shown evidence that the dead layer of the ERL HPGe detector may be larger than stated by the manufacturer, possibly due to warming up of the detector crystal. This would result in a decrease in the photopeak efficiency of up to 8 % if the dead layer of the crystal were doubled from its original size of 0.05 cm. This study shows the need for coincidence summing correction factors for the gamma lines (911.1 keV and 968.1 keV) in the 232Th series for determining accurate activity concentrations in environmental samples. For the liquid source the gamma lines, 121.8 keV, 244.7 keV, 444.1 keV and 1085.5 keV of the 152Eu series, together with the 1173.2 keV and 1332.5 keV gamma lines of the 60Co, are particularly prone to coincidence summing. In the investigation into the effects of density and volume on the photopeak efficiency for the KCl samples, it has been found that the simulated results are in good agreement with experimental data. For the range of sample densities that are dealt with by the ERL it has been found that the drop in photopeak efficiency is less than 5 %. This study shows that the uncertainty of the KCl sample activity measurement due to the effect of different filling volumes in a Marinelli beaker is estimated in the range of 0.6 % per mm and is not expected to vary appreciably with photon energy. In the case of the effect of filling height on the efficiency for the soil sample, it was found that there is a large discrepancy in the trends of the simulated and experimental curves. This discrepancy could be a result of the use of only one sand sample in this study and therefore the homogeneity of the sample has to be investigated. The effect of atomic number has been found to be negligible for the soil and sand compositions for energies above 400 keV, however if the composition of the heavy elements is not properly considered when simulating soil and sand samples, the effect of atomic number on the absolute photopeak efficiency in the low energy (< 400 keV) region can make a 14 % difference.
Emission of ³He ⁴He and ⁶He particles produce from the interaction of ¹²C with ⁹³Nb at 400 MeV incident energy
(University of the Western Cape, 2005) Mudau, Lufuno Julia; Lindsay, R; Dept. of Physics; Faculty of Science
The inclusive double di®erential cross sections of 3He, 4He, and 6He par- ticles produced from the interaction of 12C with 93Nb at 400 MeV incident energy were extracted from the prescaled singles spectra which were mea- sured in conjunction with the correlation between 8Be fragments and ® par- ticles. A further aim of this project was to test the detector e±ciencies and energy calibrations by comparing the alpha and 8Be prescaled singles data with existing inclusive cross sections of the same reaction. The absolute cross sections of 3He and 6He fragments have been extracted based on the absolute normalization of the alpha particle spectra. A study of the inclusive spectra of 3He and 6He suggest similar features to those seen in the alpha particle spectra. These features are described by the projectile break-up and nucleon coalescence mechanisms. A theoretical model which takes both these mech- anisms into account was applied to describe 3He and 6He fragments. The model is able to reproduce reasonably well the inclusive energy spectra of the 3He and 6He fragments. These results are found to be consistent with previous studies of the emission of intermediate mass fragments.
Radon in the Cango Caves
(University of the Western Cape, 2005) Nemangwele, Fhulufhelo; Lindsay, R; Dept. of Physics; Faculty of Science
Radon is a naturally occurring radioactive element in the 238U decay series that is found in high concentrations in certain geological formations such as Caves. Exposure to high concentrations of radon has been positively linked to the incidence of lung cancer. This study used Electret ion chambers and the RAD7 continuous radon monitor to measure radon concentrations in the Cango Caves in the Western Cape Province, South Africa. Measurements were taken during summer i.e. February 2004 and March 2005. The results for the radon activity concentrations range from the minimum of about 800 Bq.m-3 to a maximum of 2600 Bq.m-3. The two techniques give very similar results, though the Electret ion chamber results appear to be consistently higher by a few percent where measurements were taken at the same locations. A mathematical model has been developed to investigate the radon concentrations in the Cave. Diffusion and ventilation have been considered as mechanisms for explaining the distribution of radon concentrations. The ventilation rate in the Cave has been estimated under certain assumptions, and it is found to be about 7 ×10−6 s−1 for the Van Zyl hall which is the first large chamber in the Cave. The radon concentration increases as one goes deeper into the Cave, but then becomes fairly constant for the deeper parts. The annual effective dose that the guides are exposed to in the Cave as a result of the radon concentrations, depends strongly on the time that they spend in the Cave and in which, halls they spend most of their time in the Cave. The initial results indicate an annual effective dose of 4-10 mSv, but this needs to be further investigated.
Gamma spectroscopy of the doubly– ODD 194Tl Nucleus
(University of the Western Cape, 2006) Ramashidzha, Tshifhiwa Marius; Gueorguieva, E. A.; Lindsay, R.; Dept. of Physics; Faculty of Science
The odd – odd Tl nuclei with A ≥ 190 have moderate oblate nuclear deformation and show rotational bands built on different quasiparticle excitations. Several phenomena, not yet fully understood, were observed in these nuclei, such as large signature splitting in the yrast band (built on a πh9/2⊗νi13/2 configuration), possible non – axiality of the nuclear shape, etc. In this work the high – spin states in 194Tl were studied. The 194Tl nuclei were produced in the 181Ta (18O, 5n) 194Tl reaction at a beam energy of 93 MeV and the γ - rays were detected using the AFRODITE array. The obtained extended level scheme of 194Tl is presented and discussed in this work. CSM (Cranking shell model) and TRS (Total Routhians Surface) models were both applied to interpret the results for band 1. The results were compared with the neighboring isotone 193Hg.

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