The Environmental Radioactivity Laboratory (ERL) of iThemba LABS conducts research into levels of natural and anthropogenic radioactivity in the environment. The laboratory-based measurements are conducted using a low-background Hyper Pure Germanium (HPGe) detector system. A critical aspect of such measurements involves calibrating the detector about energy and detection efficiency. The present study details experiment that were carried to determine both energy and efficiency calibrations for various sample geometries using gamma-ray spectrometry. The measurements using reference sources of known activity were carried out using two sample holders (Marinelli Beaker (1000 ml) and, a cylindrical pill bottle (100 ml)), and a point source. The IAEA reference materials (RGU-1, RGTh-1 ore and RGK-1) were prepared and used to fill the Marinelli beaker and pill bottles. Certified reference point sources (⁶⁰Co, ¹⁵²Eu, ¹³⁷Cs, ²²Na, ²⁴¹Am and ¹³³Ba) were obtained from the National Metrology Institute of South Africa (NMISA). Experiments consisted of exposing the HPGe detector to various gamma-ray sources prepared using various sample holders and the point source geometry. The counting time for each measurement was 24 hours. Each spectrum was analysed by inserting region of interests around suitably selected photo-peaks and the counts associated with these photo-peaks were automatically determined and corrected for background by the software. The full energy peak detection efficiency was then determined from the background corrected counts, the known activity of the source and the implicit in measurement (solid angle). The experimental and simulated spectra using point sources and volume sources were compared. Both experimental and simulated spectra presented showed a good agreement in terms of shape and varying intensities as expected. Additional photo-peaks were observed from ²²Na, ⁶⁰Co, ¹³³Ba and ¹⁵²Eu (point sources) and ²³²Th and ²³⁸U (volume sources) experimental spectra these effects were not observed in the simulated spectra. These additional peaks observed are the result of coincidence summing in some of gamma emitting radionuclides. Efficiencies that were experimentally determined, were compared with the calculated efficiencies from Monte Carlo simulations using MCNPX. Efficiency calibration parameters (power fit function) for the volume sources were determined from experimental and simulated data; a = 2.58; b = -0.75 experimental and a = 1.01; b = 0.65 simulated (100 mL pill bottle) and a = 2.07; b = -0.75 experimental and a = 1.61; b = 0.66 simulated (1 L Marinelli beaker). The simulated parameters for the efficiency as determined can be used for future calculations of activity concentrations when the 100 mL pill bottle or 1 L Marinelli Beaker sample holder is used. Further improvement in these calculations can be achieved by considering the sample density. The simulation input files used to generate these values is available and can be modified to match any sample holder geometry, as well as any density that might be required in future counting.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-02-16T15:35:47Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TESE FINAL NANDIZIA SANTOS.pdf: 2193955 bytes, checksum: ad0f8d4d96ef22fde9239fd8d08f9c60 (MD5) / Made available in DSpace on 2017-02-16T15:35:47Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TESE FINAL NANDIZIA SANTOS.pdf: 2193955 bytes, checksum: ad0f8d4d96ef22fde9239fd8d08f9c60 (MD5) Previous issue date: 2016-06-27 / CAPES / A elevada concentração de urânio e tório no meio ambiente possibilita maior exposição do homem aos radionuclídeos naturais, necessitando assim, de avaliação devido aos riscos potenciais à saúde humana. No estado da Paraíba, no município de São José de Espinharas, encontra-se uma reserva de urânio, expondo, assim, seus habitantes. Amostras biológicas como cabelo e sangue podem ser utilizadas como bioindicadores para populações expostas, natural ou ocupacionalmente. O presente estudo visou a biomonitoração desses elementos em humanos, através de amostras de cabelo e sangue utilizando o ICP-MS. As concentrações sanguíneas dos doadores apresentaram-se bastante reduzidas, inferiores ao limite de detecção (0,001µg. g-1) para a metodologia proposta. Entretanto, as concentrações de urânio e tório no cabelo para os habitantes de São José de Espinharas variaram de 3,27 a 191,50 µg.g-1 e 0,30 a 9,44 µg.g-1, com médias de 20,73 µg.g-1 e 3,72 µg.g-1, respectivamente. Foram avaliados também, municípios adjacentes, sendo eles: São Mamede, São José do Sabugi e Patos. Os intervalos de concentração e as médias encontradas foram: para urânio de 10,10 a 337,20 µg.g-1 (187,24 µg.g-1 ), 17,87 a 362,38 µg.g-1 (120,90 µg.g-1 ) e 4,08 a 0,30 µg.g-1 ( 7,31 µg.g1 ); e para tório de 0,05 a 21,01 µg.g-1 (5,45 µg.g-1), 0,08 a 6,41 µg.g-1 (2,08 µg.g-1), 0,23 a 7,23 µg.g-1 (4,09 µg.g-1), respectivamente. A média geral do referido estudo foi de 68 µg.g-1 para urânio, e 3,61 µg.g-1 para o tório. Indivíduos cujas concentrações de urânio encontram-se inferiores a 100 µg.g-1 podem ser considerados como não expostos. Demonstrando este fato, os resultados de urânio e tório sérico, indicaram ausência desses elementos na corrente sanguínea. Entretanto, em amostras de cabelo, alguns doadores apresentaram concentrações superiores a este valor, necessitando assim de avaliações adicionais em matrizes diferentes, para testes confirmatórios. Concentrações de tório em cabelo são pouco pesquisadas, não havendo valores para referência. Sugerem-se análises das águas e alimentos para maiores esclarecimentos da exposição e possível intoxicação, visto que, são fontes importantes de contaminação. / The high concentration of uranium and thorium in the environment allows for greater human exposure to natural radionuclides, thus requiring, evaluation of the potential risks to human health. In the state of Paraíba, in São José de Espinharas is a uranium reserves, thereby exposing its inhabitants. Biological samples such as hair and blood can be used as bioindicators of exposed populations, natural or occupationally. The present study aimed biomonitoring of these elements in humans, through hair and blood samples using ICP-MS. Blood concentrations of the donors had to be quite low, below the detection limit (0.001µg. g1 ) for the proposed methodology. However the concentrations of uranium and thorium hair for the inhabitants of São José de Espinharas ranged from 3.27 to 191.50 μg.g-1 and 0.30 to 9.44 μg.g-1, with an average of 20.73 μg.g-1 and 3.72μg.g-1, respectively. Were also evaluated, adjacent municipalities, namely: São Mamede, São José do Sabugi and Patos. The concentration ranges and averages were: uranium to 10.10 to 337.20 μg.g-1 (187.24 μg.g-1), 17.87 to 362.38 μg.g-1 (120.90 μg.g-1) and 4.08 to 0.30 μg.g-1 (7.31 μg.g-1); and thorium from 0.05 to 21.01 μg.g-1 (5.45 μg.g-1), 0.08 to 6.41 μg.g-1 (2.08 μg.g-1), 0.23 to 7.23 μg.g-1 (4.09 μg.g-1), respectively. The overall average of the study was 68 μg.g-1 for uranium, and 3.61 μg.g-1 for thorium. Individuals whose uranium concentrations are below 100 μg.g-1 can be considered unexposed. Demonstrating this fact, the results of uranium and thorium serum, demonstrating the absence of these elements in the bloodstream. However, in hair samples, some donors presented concentrations greater than this value, thus requiring additional assessments in different matrices, for confirmatory tests. Thorium concentrations in hair are little studied, with no values for reference. It is suggested analyzes of water and food for more exposure clarification and possible poisoning, as are important sources of contamination.

Dans le cadre du Traité d'Interdiction Complète des Essais Nucléaires (TICE), le Système de Surveillance International (SSI) a été développé. Ce réseau consiste en plusieurs centaines de stations de mesures dont le rôle est de détecter la signature d'un essai nucléaire clandestin. Quatre types de mesures sont effectués: sismique, hydro-acoustique, infrason et radionucléide. Dans le cas particulier d'un essai nucléaire souterrain, seule la mesure des radionucléides est adéquate pour mettre en évidence le caractère nucléaire de l'explosion. Quatre radionucléides du xénon sont produits en masse lors d'un essai nucléaire: le 131m-Xe, le 133m-Xe, le 133-Xe, et le 135-Xe. Une faible proportion de ces gaz parvient à diffuser à travers les fissures de la cavité et se retrouver dans l'atmosphère. A cause de la dilution atmosphérique, les concentrations de ces quatre radionucléides sont extrêmement faibles et par conséquent difficiles à détecter. De plus, le bruit de fond atmosphérique ne cesse d'augmenter car ces gaz radioactifs sont également produits et relâchés par les usines de production de radio-isotopes médicaux et les centrales nucléaires. Afin de renforcer le réseau de surveillance, le CEA-DAM a proposé de développer un système de détection des radionucléides du xénon ultra-compact et mobile, afin de pouvoir effectuer des mesures de vérification directement sur site suspect, et ainsi contourner la contrainte de dilution atmosphérique. Ces travaux présentent le développement et l'optimisation de ce système. Le système a d'abord été modélisé sur ordinateur et ses performances en terme d'efficacité de détection ont été simulées par méthode de Monte-Carlo avec le logiciel Geant4. Les mesures se font en utilisant la technique de mesure en coïncidences électron/photon. En parallèle, une chaîne d'acquisition ultra-compacte a été développée, ainsi qu'un réseau de communication permettant de synchroniser en temps les différents spectromètres numériques utilisés pour le traitement du signal (protocole IEEE 1588 PTP). Les concentrations minimales détectables de ce système sont inférieures à 5 mBq/m³ pour une acquisition de 12 h, et ce pour les quatre radionucléides du xénon d'intérêt. / As part of the Comprehensive nuclear Test Ban Treaty (CTBT), an International Monitoring System (IMS) has been developed. This network consists of several hundred measuring stations whose role is to detect the signatures of a clandestine nuclear test. Four types of measurements are carried out: seismic, hydroacoustic, infrasound and radionuclide. In the particular case of an underground nuclear test, only the radionuclide measurement is adequate to detect the explosion and quantify its yield. Four xenon radionuclides with long half-lives are produced during a nuclear test: the 131m-Xe, the 133m-Xe, the 133-Xe and the 135-Xe. A small proportion of these gases may diffuse through the cracks in the cavity and end up in the atmosphere. Due to atmospheric dilution, the concentrations of these four radionuclides are extremely low and therefore difficult to detect. In addition, atmospheric background continues to increase as these radioactive gases are also produced by medical radioisotope facilities and nuclear power plants. In order to strengthen the IMS, the CEA-DAM has proposed to develop an ultra-compact and mobile system for detecting xenon radionuclides, in order to be able to carry out verification measurements directly on site, and thus to avoid the problem of atmospheric dilution. This work presents the development and optimization of this system. The system was first modelled on a computer and its performances in terms of detection efficiency were simulated by the Monte-Carlo method using Geant4 software. Measurements are made in electron-photon coincidence mode. In parallel, an ultra-compact acquisition chain has been developed, as well as a communication network to synchronize in time the various digital spectrometers used for signal processing (IEEE 1588 PTP protocol). The minimum detectable concentrations of this system are less than 5 mBq/m³ for a 12 h acquisition, for the four xenon radionuclides of interest.

Beryllium-7 is a cosmogenic radionuclide produced in the atmosphere through the spallation of nitrogen and oxygen nuclei by cosmic-ray-produced neutrons and protons. It is carried in the atmosphere attached to aerosols and is deposited on land and ocean surfaces by wet and dry deposition processes. Beryllium-7 decays by electron capture to lithium-7 and has a half-life of approximately 53 days. It is a potentially useful radionuclide for studying different natural processes. This thesis presents a collection of scientific papers on the occurrence of beryllium-7 in the natural environment, particularly in the Southeast Queensland region of Australia. It shows the results of experimental measurements and discusses their implications. Overall, this thesis contributes to advancing our understanding of the distribution and behaviour of beryllium-7 in the natural environment and provides a foundation for the development of nuclear techniques for the evaluation of environmental problems.

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.