The application of multi-concentration group mathematical modelling to the leaching of radionuclide waste-forms which have continuous porous matrix such as cemented waste form is described. The modelling is illustrated analysing a hypothetical of some transport mechanisms such as molecular diffusion, ionic migration and convective flow for release of interest radionuclide from a solidified waste form which contains discrete particles of radioactive Sr-85 nuclides into the aqueous environment. The group parameters are derived from the classical electrochemistry concept of ion transport in dilute electrolytic solution. The numerical analysis is based on the Crank-Nicolson Implicit Methods which assures the stability of the solution at a practical time step. The results show that, for a short-time period of leaching in demineralized water the leaching behavior follows the predominating diffusion mechanism. After this point, the role of other processes apparent and continue until all radionuclides in the cement waste are leached out when compared to the Semi-Infinite Diffusion model which is based on pure diffusion mechanism. The multi-concentration group model can also be applied to long-term prediction of complicated release mechanisms of the radionuclides in the waste form of a particular disposal environment, unless the variables of interest such as the corrosion rate, the chemical reaction, erosion rate and etc. are determined by experiment or theoretical hypothesis. The appropriate differential equation then can be solved by the same general numerical approach. Also, the results of the modelling indicate which parameters should be measured experimentally in order to provide a quantitative test of the hypothetical release mechanism.

Lack of accurate data for epidemiological studies of low dose radiation effects necessitates development of dosimetric models allowing prediction of cancer risks for different organs. The objective of this work is to develop a model of the radiation response of human bronchiolar tissue with single cell resolution. The computer model describes epithelial tissue as an ensemble of individual cells, with the geometry of a human bronchiole and the properties of different cell types are taken into account. The model simulates the tissue kinetics and radiation exposure in four dimensions: three spatial dimensions and a temporal dimension. The bronchiole is modeled as a regular hollow cylinder with the epithelial cells of three different types (basal, secretory, and ciliated) lining its interior. For the purposes of assessment of radiation damage to the cells only the nuclei of the cells have been modeled. Subroutines describing cellular kinetics have been developed to simulate cell turnover in a normal epithelial tissue. Monte Carlo subroutines have been developed to simulate exposure to alpha particles; the GEANT4 toolkit has been used to simulate exposure to low LET radiation. Each hit cell is provided with a record of energy deposition, and this record is passed to the progeny if the cell survives. The model output provides data on the number of basal progenitor cells in different phases of a cell life-cycle and secretory to ciliated cell ratio after several generations of cell proliferation. The model calculates labeling and mitotic indices and estimates the average cell turnover time for the bronchiolar tissue. Microdosimetric calculations are performed for cells traversed by ionizing particles. The model will be used to assess the accumulation of damage in cells due to protracted low level radiation exposure. The model output may provide directions for the future experimental design.

No description available.

Thesis (MTech Biomedical Technology)--Cape Peninsula University of Cape Town, 2005 / In clinical radiotherapy, experiments are performed to determine optimal conditions of the radiation prior to radiotherapy. These experiments focus on the relative biological effectivness(RBE) determination and are predominantly applied in high linear energy transfer (LET) radiations i.e. fast neutrons, as the RBE values for such radiations vary greatly. In general, the RBE of a certain radiation relative to a given reference radiation flCo gamma) varies widely with the energy, dose, dose rate, fractionation, type of tissue and end-point used. Experience with neutron therapy at iThemba LABS has shown that treatment with more fractions and lower doses per fraction may be beneficial for some patients. To calculate the iso-effective treatment dose needed, an appropriate alp ratio for early effects is needed. In this study, the repair of mouse jejunum was measured for split-dose irradiations to determine if a suitable alP ratio for neutrons could be estimated using the known value for gamma rays and the applicable RBE.. Crypt stem cell survival was measured 3.5 days after split-dose exposures to p(66)/Be neutrons and 6OCo gamma rays. Dose response curves for both treatment modalities and for both acute and fractionated exposures were constructed by counting crypts of Leiberkhiin at the base of the villi in haematoxylin and Eosin-stained sections of mouse jejunum. Using a RBE value of 1.64 and an alP ratio of 7Gy noted for tbe fractionated photon exposures, an alP ratio of 11.5 IV could be estimated for neutrons.

Graduation date: 1999

Thesis (MTech (Biomedical Technology))--Cape Technikon, Cape Town, 2004 / The need for radiobiological research was bom from the discovery that high doses of radiation could cause cancer and other health effects. However, recent developments in molecular biology uncovered the effects of low doses of radiation on different biological systems and as a result new techniques have been developed to measure these effects. The aim of this study was thus to validate biomarkers of initial DNA strand breaks, micronucleus formation, and the different pt ;ases of apoptosis as biological indicators of low-dose radiation damage. Furthermore, the difference in response of blood cells to different qualities and doses of radiation was investigated by irradiating cells with low- and high-LET radiation simultaneously. Blood from one donor was irradiated with doses between 0 and 4 Gy gamma- and neutron radiation. The alkaline single-cell gel electrophoresis (comet) assay was performed on different cell preparations directly after irradiation for the detection of initial DNA strand breaks. Radiation-induced cytogenetic damage was investigated using the cytokinesis-blocked micronucleus assay while different features of apoptosis were investigated by measuring caspase activation, enzymatic DNA fragmentation, and cellular morphology. The comet assay was sensitive enough to detect DNA strand breaks above 0.25 Gy and showed that the Iymphocyte isolation process induced some endogenous damage in cells, detected by the formation of highly damaged cells and hedgehogs in isolated cell preparations only.

Thesis (DTech (Biomedical Technology))--Cape Technikon, 2001 / Ionising radiation has the ability to induce, inter alia, DNA damage and is well established as a causative agent of carcinogenesis and mutagenesis. The effects of high doses of short duration have been well documented, whereas the effects of continuous exposure to low doses of ionising radiation have not, nor are they as clearly understood and current risk estimates are largely extrapolated from high-dose data of atomic bomb survivors. This study evaluated the clastogenic effects of low dose ionising radiation on a population of bats (Chiroptera) residing in an abandoned monazite mine. Bats were sampled from two areas in the mine, with external radiation levels measuring around 20 µSv/h (low dose) and 100 µSv/h (high dose). A control group of bats was collected from a cave with no detectable radiation above normal background levels. The most frequently encountered genetic event in human malignancy is the alteration of the p53 gene. Mutant p53 proteins have a longer half-life than the wild-type variant and accumulate to high levels in the nucleus of tumour cells. The study showed that not only was there a significant increase in p53 positive cells of radiation exposed bats, but also in the degree of positivity, especially in the cells lining the bronchioles of the lungs. Although experimental studies have shown that exposure to radiation may lead to the onset of fibrosis and an inflammatory response in the lung and other tissues, the magnitude of the dose exposure was not comparable to this study and histological examination of bat lung and liver tissues showed no morphological changes in radiation exposed bats when compared to the control group. It has been documented that chronic radiation exposures may give rise to a number of specific haematological defects which are collectively termed "preleukemia" or myelodysplastic syndrome. Full blood counts on bat samples showed a significant decrease in the MCV indicating microcytic erythrocytes from the radiation exposed bats. Differential counts performed on the peripheral blood of the bats showed a marked neutropenia. Neutrophils also showed marked dysplasia including psuedo-Pelger Huet cells in radiation-exposed bats. Cytochemical analysis using DAB myeIoperoxidase showed that control bats had hypogranular neutrophils andradiation-exposedbats had largely '1granularneutrophils. Bonemarrow biopsies were taken from both control and radiation-exposed bats and evaluated for ceIlularity, granulocyte: lymphocyte: erythrocyte (GLE) ratio and megakaryocyte morphology. A hypocelIular bone marrow, a decreased granulocytic haematopoeisis and dysplastic megakaryocyte morphology were observed in radiation-exposed bats. Mineralisation of bone osteoid was determined using image analysis and showed a highly significant decrease in the bone matrix from radiation-exposed bats. All haematological features observed are congruent with current literature describing secondary (radiation-induced) myelodysplastic syndrome.

Laser application in the field of biological and medical sciences has significantly grown, thereby strengthening the field of Biophotonics. Research conducted in Biophotonics focuses on the concept of using light especially in the visible and near infrared regions of the electromagnetic radiation for the evaluation of living systems. In this thesis new discoveries are presented about low level laser therapy, optical trapping, transmission spectroscopy, luminescence spectroscopy and structured illumination microscopy (SIM), displaying the impact each technique has on HIV infected cells. The results showed that the irradiation of HIV-1 infected TZM-bl cells with low power red laser reduces HIV-1 infection. The outcomes of this study further proved that when irradiation is used in conjunction with efavirenz, an antiretroviral drug, HIV-1 infection could be reduced to undetectable levels in TZM-bl cells. Through the coupling of transmission spectroscopy with optical trapping, and separately, use of luminescence spectroscopy, label free diagnosis of HIV in infected cell samples was achieved. This finding affirms that HIV-1 infection can be detected in a label free manner when using laser based techniques. Furthermore, the photoluminescence spectrometer system was employed to generate a decay curve, which was necessary so as to have some understanding on lifetime of the luminescent signal in infected TZM-bl cells. Finally, in order to confirm that indeed TZM-bl cells were infected, an established super-resolution microscopy system SIM was used to detect HIV-1 infection in TZM-bl cells. Indeed in the infected cells viral molecules p24 and gp41 were detected through SIM, while they were not detected in uninfected cells. In future studies, super resolution microscopy would be coupled to an optical trapping system in order to confirm that each trapped cells is whether infected or uninfected so as to improve HIV diagnosis. / College of Science, Engineering and Technology / Ph. D. (Science, Engineering and Technology)