>Magister Scientiae - MSc / The Physics Department at the University of the Western Cape and the Environmental Physics group at iThemba labs have been conducting radiometric studies on both land and water. In this study a 7.5 cm X 7.5 cm NaI (Tl) detector was used to study activity concentrations of primordial radionuclides in soil and sand samples. The detector and the sample were placed inside a lead castle to reduce background in the laboratory from the surroundings such as the wall and the floor. The samples were placed inside a 1 L Marinelli beaker which surrounds the detector for better relative efficiency as almost the whole sample is exposed to the detector. Additional lead bricks were placed below the detector to further reduce the background by 20%. The NaI detector is known to be prone to spectral drift caused by temperature differences inside and around the detector. The spectral drift was investigated by using a ¹³⁷Cs source to monitor the movements in the 662 keV peak. The maximum centroid shift was about 4 keV (for a period of 24 hours) which is enough to cause disturbances in spectral fitting. There was no correlation between the centroid shift and small room temperature fluctuations of 1.56 ºC. A Full Spectrum Analysis (FSA) method was used to extract the activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K from the measured data. The FSA method is different from the usual Windows Analysis (WA) as it uses the whole spectrum instead of only putting a ‘window’ around the region of interest to measure the counts around a certain energy peak. The FSA method uses standard spectra corresponding to the radionuclides being investigated, and is expected to have an advantage when low-activity samples are measured. The standard spectra are multiplied by the activity concentrations and then added to fit the measured spectrum. Accurate concentrations are then extracted using a chi-squared (χ²) minimization procedure. Eight samples were measured in the laboratory using the NaI detector and analyzed using the FSA method. The samples were measured for about 24 hours for good statistics. Microsoft Excel and MATLAB were used to calculate the activity concentrations. The ²³⁸U activity concentration values varied from 14 ± 1 Bq/kg (iThemba soil, HS6) to 256 ± 10 Bq/kg (Kloof sample). The ²³²Th activity concentration values varied from 7 ± 1 Bq/kg (Anstip beach sand) to 53 ± 3 Bq/kg (Rawsonville soil #B31). The ⁴⁰K activity concentration values varied from 60 ± 20 Bq/kg (iThemba soil, HS6) to 190 ± 20 Bq/kg (Kloof sample). The χ² values also varied from sample to sample with the lowest being 12 (Anstip beach sand) and the highest (for samples without contamination of anthropogenic nuclei) being 357 (Rawsonville soil #B28). A high χ² value usually represents incomplete gain drift corrections, improper set of fitting functions, proper inclusion of coincidence summing or the presence of anthropogenic (man made) radionuclei in the source [Hen03]. Activity concentrations of ⁴⁰K, ²³²Th and ²³⁸U were measured at four stationary points on the Kloof mine dump. The fifth stationary point was located on the Southdeep mine dump. These measurements were analysed using the FSA method and fitting by "eye" the standard spectra to the measured spectra using Microsoft Excel. These values were then compared to values obtained using an automated minimization procedure in MATLAB. There was a good correlation between these results except for ²³²Th which had higher concentrations when MATLAB was used, where 16 Bq/kg was the average value in Excel and 24 Bq/kg was the average value in MATLAB.

Tumor functional volume (FV) and its mean activity concentration (mAC) are the quantities derived from positron emission tomography (PET). These quantities are used for estimating radiation dose for a therapy, evaluating the progression of a disease and also use it as a prognostic indicator for predicting outcome. PET images have low resolution, high noise and affected by partial volume effect (PVE). Manually segmenting each tumor is very cumbersome and very hard to reproduce. To solve the above problem I developed an algorithm, called iterative deconvolution thresholding segmentation (IDTS) algorithm; the algorithm segment the tumor, measures the FV, correct for the PVE and calculates mAC. The algorithm corrects for the PVE without the need to estimate camera’s point spread function (PSF); also does not require optimizing for a specific camera. My algorithm was tested in physical phantom studies, where hollow spheres (0.5-16 ml) were used to represent tumors with a homogeneous activity distribution. It was also tested on irregular shaped tumors with a heterogeneous activity profile which were acquired using physical and simulated phantom. The physical phantom studies were performed with different signal to background ratios (SBR) and with different acquisition times (1-5 min). The algorithm was applied on ten clinical data where the results were compared with manual segmentation and fixed percentage thresholding method called T50 and T60 in which 50% and 60% of the maximum intensity respectively is used as threshold. The average error in FV and mAC calculation was 30% and -35% for 0.5 ml tumor. The average error FV and mAC calculation were ~5% for 16 ml tumor. The overall FV error was ~10% for heterogeneous tumors in physical and simulated phantom data. The FV and mAC error for clinical image compared to manual segmentation was around -17% and 15% respectively. In summary my algorithm has potential to be applied on data acquired from different cameras as its not dependent on knowing the camera’s PSF. The algorithm can also improve dose estimation and treatment planning.

<p>²²⁶Ra is a radionuclide of much concern since it poses a high risk of radio-toxicity when ingested and is well known for its invariably long half life of 1600 years. As such ²²⁶Ra concentrations were measured in whole body tissue of fathead minnows (Pimephales promelas) in an experimental set up. Fathead minnows obtained were about two months old and fed on a Radium-226 spiked diet until 115 days. A simple and direct method to determine ²²⁶Ra ingested by fish using a homogeneous liquid scintillation counting was developed. The study consisted of three groups; a sham, Radium treatment and acid treatment. Fathead minnows were sampled 75 and 115 days after feeding, and the following end points; mass (w/w), length, specific growth rate, condition factor and radionuclide measurements obtained. Mean end point results were (0.24 ± 0.03 g), (2.78 ± 0.1 cm), (1.75 ± 0.13 % day^-1), (1.10 ± 0.06 g cm^-3) and (577.06 ± 572.13 mBq g^-1) respectively. Also mean total ²²⁶Ra level was calculated as (1911.43 ± 868.64 mBq g^-1) while the activity in sham and acid treatment resulted in levels below the Minimum Detectable Activity of 7.46 mBq g^-1. The mean rate of ²²⁶Ra accumulation, known as the concentration factor, by the fathead minnows was determined as 0.35 ± 0.19. Assuming that the ²²⁶Ra Isotope is evenly distributed in the fish whole body, the derived dose rate was found to be 5.26 μGy h^-1.</p> / Master of Science (MSc)

<p><font face="TimesNewRomanPSMT"> <p align="left">Natural radioactivity studies have been carried out to study the textural characteristics, heavy mineral composition, provenance, sediment transport, and depositional environment of beach placer deposits. The naturally occurring radionuclides such as properties of beach sands, which reflect the geological characteristics such as transport and sorting processes and the depositional environment. The present work focuses on the radiometric characteristics of beach sand deposits along the west coastof South Africa. Beach sands samples were collected at the Melkbosstrand (MBS) and Ouskip (OSK) beach. The activity concentrations of these radionuclides were determined by high-resolution gamma-ray spectrometry using a high-purity germanium (HPGe) detector in a low-background configuration.</p> </font></p>

<p><font face="TimesNewRomanPSMT"> <p align="left">Natural radioactivity studies have been carried out to study the textural characteristics, heavy mineral composition, provenance, sediment transport, and depositional environment of beach placer deposits. The naturally occurring radionuclides such as properties of beach sands, which reflect the geological characteristics such as transport and sorting processes and the depositional environment. The present work focuses on the radiometric characteristics of beach sand deposits along the west coastof South Africa. Beach sands samples were collected at the Melkbosstrand (MBS) and Ouskip (OSK) beach. The activity concentrations of these radionuclides were determined by high-resolution gamma-ray spectrometry using a high-purity germanium (HPGe) detector in a low-background configuration.</p> </font></p>

Magister Scientiae - MSc / Natural radioactivity studies have been carried out to study the textural characteristics, heavy mineral composition, provenance, sediment transport, and depositional environment of beach placer deposits. The naturally occurring radionuclides such as 232Th, 238U and 40K are used as the tracers of the mineralogical properties of beach sands, which reflect the geological characteristics such as transport and sorting processes and the depositional environment. The present work focuses on the radiometric characteristics of beach sand deposits along the west coast of South Africa. Beach sands samples were collected at the Melkbosstrand (MBS) and Ouskip (OSK) beach. The activity concentrations of these radionuclides were determined by high-resolution gamma-ray spectrometry using a high-purity germanium (HPGe) detector in a low-background configuration.

This thesis provides the measurements of 222Rn exhalation rates, 210Pb deposition rates and excess 210Pb inventories for locations in and around Ranger Uranium Mine and Jabiru located within Kakadu National Park, Australia. Radon-222 is part of the natural 238U series decay chain and the only gas to be found in the series under normal conditions. Part of the natural redistribution of 222Rn in the environment is a portion exhales from the ground and disperses into the atmosphere. Here it decays via a series of short-lived progeny, that attach themselves to aerosol particles, to the long lived isotope 210Pb (T1/2 = 22.3 y). Attached and unattached 210Pb is removed from the atmosphere through wet and dry deposition and deposited on the surface of the earth, the fraction deposited on soils is gradually transported through the soil and can create a depth profile of 210Pb. Here it decays to the stable isotope 206Pb completing the 238U series. Measurements of 222Rn exhalation rates and 210Pb deposition rates were performed over complete seasonal cycles, August 2002 - July 2003 and May 2003 - May 2004 respectively. The area is categorised as wet and dry tropics and it experiences two distinct seasonal patterns, a dry season (May-October) with little or no precipitation events and a wet season (December-March) with almost daily precipitation and monsoonal troughs. November and April are regarded as transitional months. As the natural processes of 222Rn exhalation and 210Pb deposition are heavily influenced by soil moisture and precipitation respectively, seasonal variations in the exhalation and deposition rates were expected. It was observed that 222Rn exhalation rates decreased throughout the wet season when the increase in soil moisture retarded exhalation. Lead-210 deposition peaked throughout the wet season as precipitation is the major scavenging process of this isotope from the atmosphere. Radon-222 is influenced by other parameters such as 226Ra activity concentration and distribution, soil porosity and grain size. With the removal of the influence of soil moisture during the dry season it was possible to examine the effect of these other variables in a more comprehensive manner. This resulted in categorisation of geomorphic landscapes from which the 222Rn exhalation rate to 226Ra activity concentration ratios were similar during the dry season. These results can be extended to estimate dry season 222Rn exhalation rates from tropical locations from a measurement of 226Ra activity concentration. Through modelling the 210Pb budget on local and regional scales it was observed that there is a net loss of 210Pb from the region, the majority of which occurs during the dry season. This has been attributed to the fact that 210Pb attached to aerosols is transported great distance with the prevailing trade winds created by a Hadley Circulation cell predominant during the dry season (winter) months. By including the influence of factors such as water inundation and natural 210Pb redistribution in the soil wet season budgeting of 210Pb on local and regional scales gave very good results.