A total of 10 vertical 226Ra profiles from the North Pacific was published as part of the GEOSECS program. These profiles are located on an east-west section along ~300N. The purpose of this thesis is to use one-dimensional and two-dimensional diffusion-advection models to estimate some important geochemical parameters. There are some discrepancies between the modeling results and the observed tracer distributions due to restrictions on end-members in the models. Fitting the observed data to the model, one obtains values of the Z* between 0.8 and 1.0 km from potential temperature and that of JBa/w between 0.0020 and 0.0064 nM/kg/m from Ba. Where Ba profiles are available, the corresponding 226Ra profiles are similar from the surface to the deep water, showing a linear correlation with a slope at 0.22 dpm/100nM or 4.4¡Ñ10-9 for the Ra/Ba molal ratio. The slope has an intercept of 0.48 nM/kg on the Ba axis. That 226Ra is linearly correlated with Ba from surface water to deep water is probably because algebraic sum of the production term and the radioactive decay is nearly constant. Thus the revised model has a form equivalent to that for Ba. Where Ba profiles are available, one can fit the observed data to the model to obtain the needed parameters with (JRa-£fCRa)/JBa as a constant. The upwelling velocity, w, obtained from model calculations on the Ba profiles is: 3.8 m/yr at 204; 4.8 m/yr at 212; 3.5 m/yr at 226, 1.2 m/yr at 224. These values are consistent with those (1 to 12m/yr) reported for the Pacific deep water based on other methods. Fitting 226Ra profile data to the vertical one-dimensional diffusion-advection model for the in-situ production rate, J, and the associated upwelling velocity, w, one finds that J and w are coupled with a negative correlation. This is consistent with that reported in the literature. Profiles from the northeast Pacific show a deep Ra maximum, with an ¡§excess¡¨ which extends westward while decreasing and finally vanishing in the northwest Pacific near Japan. A horizontal diffusivity of 5 ¡Ñ105 cm2/s was obtained based on this ¡§excess¡¨ 226Ra with a horizontal 1-D model by Chung and Craig (1980). A numerical finite-difference method is applied to the 2-D model fitting on the potential temperature data for the horizontal diffusivity, Kx. A Kx of 4.58 ¡Ñ105 cm2/s is obtained within the depth range of 1000m to 3000m. The value is 4.82 ¡Ñ105 cm2/s for the depth range from 1000m to 4000m. These two approaches yield nearly identical results.

Radium contamination in the lakes near uranium mines and its intake by fish and other aquatic species are of great concern in environmental radiation protection. As an alternative technique to Liquid Scintillation Counting, we present a gamma-ray spectrometric method for low level 226Ra analysis, particularly in live fish. The HyperPure Ge and a 4π NaI(Tl) array were employed as gamma-ray spectrometers. The 226Ra spectra for each spectrometer were collected in order to compare their analytical performance. From the HPGe 226Ra spectra, a detection limit of 6.81 Bq with 99% confidence was determined for an hour counting with the three strongest peaks combined. For the 4π NaI(Tl) 226Ra spectra, in order to optimize the spectral analysis, a method applied to nine different energy regions was attempted and it turned out that the detection limit is best when the total integral count subtracted by the corresponding background is used. The detection limit of the 4π NaI(Tl) was 0.99 Bq with 99% confidence for one hour counting. A benchmark simulation for point source position dependence on relative peak efficiency showed a good agreement with the experimental data. To extend 226Ra analysis to volumetric aqueous samples, MCNP Monte Carlo simulations showed that for three cylindrical volume sources, as the simulated volume source size increased from 60 ml to 125 ml to 250 ml, the full-energy peak efficiency in the energy range of interest for 226Ra decreased by approximately 3% for each size increase, due to attenuation in the source volume. A method has been proposed in order to demonstrate this technique for a live fish, whereby a fish injected with 226Ra would be kept in its own special aquarium and its gamma-ray spectrum collected. / Thesis / Master of Science (MSc)

O 226Ra é um dos isótopos mais importantes da série radioativa natural do urânio em termos de dose radiológica, devido à sua relativa longa meia-vida (1.600 anos) e sua elevada radiotoxicidade. O Ministério da Saúde publicou na portaria MS nº 2914 de 12/12/2011, que dispõe sobre os procedimentos de controle e de vigilância da qualidade da água para consumo humano e seu padrão de potabilidade, os limites máximos permitidos para este radionuclídeo. As demandas por essas determinações aumentaram, justificando o desenvolvimento de técnicas mais rápidas e mais precisas para a determinação deste radionuclídeo, uma vez que a técnica utilizada rotineiramente leva cerca de 38 dias para esta determinação. Foram ensaiados três métodos diferentes para a determinação do 226Ra, com algumas alterações realizadas em relação aos métodos originais. O método desenvolvido por Roman, que não realiza a purificação do rádio, fazendo somente o procedimento de eletrodeposição de soluções padrão, seguido de contagem no espectrômetro alfa, se mostrou ineficaz, com rendimentos de recuperação muito baixos e com baixa resolução espectral. O método desenvolvido pelo Departamento de Energia (DOE) dos Estados Unidos realiza a purificação e utiliza 224Ra como traçador. A purificação é conduzida por meio de resina de troca catiônica, com posterior eletrodeposição e contagem. O método ensaiado indicou a presença de interferentes e o rendimento de recuperação de rádio não apresentou um bom resultado; a resolução espectral foi mediana, além disso, seu traçador é um isótopo natural e requer um procedimento extremamente trabalhoso, com determinações radioquímicas em duplicata. O método desenvolvido por Crespo foi sendo sucessivamente modificado e complementado, até o desenvolvimento de um novo método. O método usa 225Ra como traçador. O rádio foi purificado utilizando resina Ln® e resina de troca catiônica, e eletrodepositado sobre um disco de aço inoxidável a partir de uma solução de oxalato de amônio, e posteriormente contado por espectrometria alfa. Este método produziu espectros com altas resoluções e altos rendimentos de recuperação de 226Ra, além de permitir uma significativa redução do tempo necessário para a determinação de 226Ra nas amostras de água potável, em torno de 4 dias, em comparação com outros métodos, que podem chegar a 20 ou 38 dias para se quantificar este radionuclídeo. / 226Ra is one of the most important radioactive isotopes of natural uranium series in terms of radiation dose, due their relative long half-life (1,600 years) and high radiotoxicity. The Ministry of Health published Ordinance MS nº 2914 of 12/12/2011, which establishes procedures for control and surveillance of water quality for human consumption and its potability standard, the maximum limits allowed for this radionuclide. Demands for these determinations increased, justifying the development of faster and more accurate techniques for determination this radionuclide, since the technique used routinely takes about 38 days for this determination. Three different methods for determination of 226Ra were tested, with some changes made from the original methods. The method developed by Roman, which does not perform purification of radium, only making electrodeposition procedure for standard solutions, followed by alpha spectrometer counting, was ineffective, with very low recovery yields and with low spectral resolution. The method developed by United States Department of Energy (DOE) performs purification and uses 224Ra as yield tracer. Purification is carried out by means of cation exchange resin with subsequent electrodeposition and counting. The method tested indicated presence of interfering, and recovery yield of radium did not provide good result; spectral resolution was median, moreover, its yield tracer is a natural isotope and requires an extremely laborious procedure with radiochemical determinations in duplicate. The method developed by Crespo was being successively modified and complemented by the development of a new method. The method uses 225Ra as yield tracer. Radium was purified using Ln® resin and cation exchange resin and electrodeposited on a stainless steel disc from solution of ammonium oxalate, and counted by alpha spectrometry. This method produced spectra with high resolutions and high recovery yields of 226Ra. Furthermore, the method allows significant reduction in time required for determination of 226Ra in drinking water samples, around 4 days, in comparison with other methods, which can reach 20 or 38 days to quantify this radionuclide.

ABSTRACT This thesis was to develop a simplified technique for the analysis of 210Pb in sediment samples with gamma spectrometry. Compared with the results of the conventional beta method, we found that the gamma method yields values that are 1.5 times higher. This discrepancy awaits further investigation. However, the results determined on two sediment-trap samples and a 210Pb source by the gamma technique agree within 10 % to those determined by the same method at the Institute of Earth Sciences, Academia Sinica. Also, using the manganese-impregnated fiber extraction technique, the distributions of 228Ra and 226Ra in surface waters around Taiwan and in the northern South China Sea¡]SCS¡^ were measured by a high-purity germanium¡]HPGe¡^ detector coupled with gamma spectrometry. The distribution of 228Ra in the surface sea water off eastern Taiwan was controlled by its source function, horizontal mixing and dilution of the Kuroshio. It was higher in coastal or estuarine areas but much lower farther away from the coast line. The 228Ra/226Ra activity ratio¡]AR¡^ varied in the same trend. Estuaries and coastal zones in eastern Taiwan were probably the main source for 228Ra in the adjacent sea. Concentrations of 226Ra on transect LY, CC and PN were almost constant. The AR values along the transect CC were lower than unity, because there was no estuarine input and it was entirely occupied by the Kuroshio water. The concentration of 228Ra along this transect was about 30 % higher in summer than in spring, probably because 228Ra was preferentially released from the coastal sediments by typhoon Nichole. Applying a steady-state one-dimensional diffusion model to the LY and PN lines extending from the estuarine coastal areas, we estimated a horizontal eddy diffusion coefficient of about 1.3 ¡Ñ 105 cm2/s for the sea off eastern Taiwan. This value is comparable to that of the Japan Sea determined by Nozaki et al.¡]1989¡^. Taiwan Strait¡]TS¡^ is mainly continental shelf with water depth less than 50 m on the average. Ra isotopes in the surface water were probably supplied by diffusion from the bottom sediments; their distributions were affected by currents and tides, and so no clear trend could be recognized when sampling was conducted in different times. 228Ra was seen inversely correlated with salinity, showing effect of the fresh water. Concentrations of 228Ra and 226Ra along the transect CS decreased away from the estuary during the spring. The 228Ra values along the TS transect in the same season increased toward the northwest, suggesting a possible source from the coastal zone of the mainland. Distribution of 228Ra in the northern SCS was determined consecutively in 2000 and 2001. The 228Ra activities in the northern continental shelf and northwestern Luzon were higher than in the central region during the spring season. The NE monsoon prevails in fall and winter causing the longshore current to transport the shelf water of high 228Ra to the central region. The 228Ra activities of surface water decreased southward and so the central region away from land had low 228Ra values. The low 228Ra concentration observed at the sea off southern Taiwan was probably due to dilution by the Kuroshio. Based on the 228Ra distribution along a transect roughly perpendicular to the 200m bathymetric contour, we calculated a horizontal eddy diffusion coefficient, Kh of about 6.2 ¡Ñ 106 cm2/s, a value lower than that estimated by Huang et al.¡]1996¡^in the Nansha sea area. Compared to the Kh values estimated for the northwest Pacific by Yamada and Nozaki¡]1986¡^, this value falls in between those within and without 200 km away from land in the Kuroshio region.

In der Arbeit werden nach einer detaillierten Beschreibung der eingesetzten Böden mit erhöhter Konzentration an den Radionukliden 210Pb, 226Ra, 227Ac, 230Th und 238U und der angewandten Analysenverfahren eine umfangreiche Übersicht über die Transferfaktoren Boden - Pflanze für die einzelnen Pflanzenteile der in der menschlichen Ernährung genutzten Gemüse und in Futterpflanzen vorgestellt. Die gammaspektrometrischen Bestimmungen von geringen Radioaktivitäten wurden einem Untertagemesslabor durchgeführt. Die Unterschiede in den Transferfaktoren für die Pflanzen und deren Teile und Böden und die Beziehungen zwischen Transferfaktoren und eluierbaren Anteilen der Böden, Pflanzenteile; sowie zwischen den radioaktiven Elementen Radium und Actinium und den Elementen Barium und Lanthan wurden dargestellt. Es wurde bei den Pflanzen eine Abnahme der Radioaktivität von der Wurzel über Stängel und Blatt zur Frucht festgestellt. Die Transferfaktoren für das bisher kaum bestimmten 227Ac ist relativ hoch und liegt in der Größenordnung der sehr konservativ angesetzten Richtwerte des Strahlenschutzes, während sie für die anderen Radionuklide weit unter den Richtwerten liegen. / The used soils with enhanced activity of the radionuclides 210Pb, 226Ra, 227Ac, 230Th, and 238U and the analytical methods for the determination of soil-plant transfer factors are described and a survey of the obtained values for parts of plants used for human nutrition are presented. Gamma spectrometric determination of low radioactivities has been performed in an underground laboratory. For comparison the factors are determined for the plants of similar elements Ba for Ra and La for Ac. In all cases the values decreases from the roots over the leaves to the fruits. The values for 227Ac are relatively high and are in the magnitude of the „Richtwerte“ for radiation protection, in spite of the other radionuclides, which are lower than the „Richtwerte“.

In der Arbeit werden nach einer detaillierten Beschreibung der eingesetzten Böden mit erhöhter Konzentration an den Radionukliden 210Pb, 226Ra, 227Ac, 230Th und 238U und der angewandten Analysenverfahren eine umfangreiche Übersicht über die Transferfaktoren Boden - Pflanze für die einzelnen Pflanzenteile der in der menschlichen Ernährung genutzten Gemüse und in Futterpflanzen vorgestellt. Die gammaspektrometrischen Bestimmungen von geringen Radioaktivitäten wurden einem Untertagemesslabor durchgeführt. Die Unterschiede in den Transferfaktoren für die Pflanzen und deren Teile und Böden und die Beziehungen zwischen Transferfaktoren und eluierbaren Anteilen der Böden, Pflanzenteile; sowie zwischen den radioaktiven Elementen Radium und Actinium und den Elementen Barium und Lanthan wurden dargestellt. Es wurde bei den Pflanzen eine Abnahme der Radioaktivität von der Wurzel über Stängel und Blatt zur Frucht festgestellt. Die Transferfaktoren für das bisher kaum bestimmten 227Ac ist relativ hoch und liegt in der Größenordnung der sehr konservativ angesetzten Richtwerte des Strahlenschutzes, während sie für die anderen Radionuklide weit unter den Richtwerten liegen. / The used soils with enhanced activity of the radionuclides 210Pb, 226Ra, 227Ac, 230Th, and 238U and the analytical methods for the determination of soil-plant transfer factors are described and a survey of the obtained values for parts of plants used for human nutrition are presented. Gamma spectrometric determination of low radioactivities has been performed in an underground laboratory. For comparison the factors are determined for the plants of similar elements Ba for Ra and La for Ac. In all cases the values decreases from the roots over the leaves to the fruits. The values for 227Ac are relatively high and are in the magnitude of the „Richtwerte“ for radiation protection, in spite of the other radionuclides, which are lower than the „Richtwerte“.

Ce travail porte sur le comportement du Ra au sein d’un écosystème forestier (Montiers, Meuse). Il s’appuie sur la mesure de plusieurs traceurs isotopiques (déséquilibres radioactifs, rapports 228Ra/226Ra et 87Sr/86Sr) dans les différents compartiments du système eau-sol-plante. Les objectifs étaient : 1) d’étudier la mobilité du Ra et ses ascendants radioactifs entre les fractions minérales séparées d’un profil de sol, 2) d’évaluer le transfert du Ra vers les compartiments eau-plante de l’écosystème, 3) de caractériser le transfert du Ra et son temps de résidence dans la végétation, 4) de réaliser le bilan du cycle biogéochimique du Ra. Ce travail montre une forte redistribution de U, Th et Ra en fonction de leurs affinités respectives avec les différentes fractions minérales du sol. Bien que le Ra soit très fortement associé à la fraction fine (< 2µm) du sol, la végétation (hêtres) semble prélever le Ra des oxydes de fer du sol. Le transfert ultérieur de ce nucléide depuis les racines vers les parties aériennes de l’arbre est moins important que celui des autres alcalino-terreux, aboutissant à un temps de résidence dans la végétation de l’ordre de quelques années (2.6 ± 1.6 ans). Enfin, le cycle biogéochimique du Ra est caractérisé par un flux de dégradation de la litière souterraine plus important que celui lié à la litière de surface, par un apport atmosphérique en Ra négligeable et par un flux d'altération très important, ce dernier ne transitant pas par les solutions de sols gravitaires. Le Ra présent dans ces dernières provient presque exclusivement de la dégradation de la litière. / This work investigates the behaviour of Ra within a forest ecosystem (Montiers, Meuse). It is based on the quantification of several isotopic tracers (U- and Th- series disequilibria, isotopic ratios of 228Ra/226Ra and 87Sr/86Sr) in the different compartments of the water-soil-plant system. The research goals were : 1) to study the mobility of Ra and its radioactive ascendants in the separated mineral fractions of a soil profile, 2) to evaluate the transfer of Ra to the water-plant system, 3) to characterise the transfer of Ra and its residence time onto the vegetation, 4) to realise an account of the biogeochemical cycle of Ra. This work shows a strong redistribution of U, Th and Ra depending on their respective affinities with the different mineral fractions of the soil. Despite being predominantly concentrated in the clay fraction (<2 µm) of the soil, our findings indicate that trees (beeches) mostly extract Ra from the soil’s iron oxides. The subsequent transfer of this nuclide from the roots to the foliage is lesser than that of other alkaline-earth metals, leading to a vegetal residence time on the order of a few years (2.6 ± 1.6 years). Finally, the biogeochemical cycle of Ra is characterised by the degradation flux of fine-roots rather than that of leaves, by a negligible atmospheric input and by a strong weathering rate. Ra presents in the latter originates almost uniquely from litter degradation and does not pass through gravitational soil solutions.