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Radiochemical methods before measurement are indispensable to determine Iodine-129 by Accelerator Mass Spectrometry (AMS) in environmental samples. In particular, in sediments, iodine is associated with both inorganic and organic matter, and it presents in several chemical forms. Therefore, the radiochemical procedure must be designed to extract all the different iodine species from the matrix, whilst being as robust and time effective as possible. In this work, different microwave digestion methods, together with the processing of the iodine species to be measured by AMS, were tested and their performances are presented here. Two sediment cores, one with muddy sediment (core A) and one with permeable sandy sediment (core I), collected in the Celtic Sea, were used and the results were evaluated to determine an optimized iodine extraction. The method consisted of a microwave digestion with concentrated nitric acid followed by a double liquid–liquid extraction and the final precipitation of silver iodide (AgI), required to measure iodine by AMS. Back extraction of iodine in a reducing solution during purification was carried out with hydrazine (NH2-NH2). Subsequent additional steps were added to optimize all iodine species extraction. First, hydrochloric hydroxylamine (NH2OH·HCl) and sodium bisulfite (Na2S2O5) were used to homogenize all iodine species before extraction through a redox process. Second, sodium hypochlorite (NaOCl) was added to remove any final organic matter after digestion. The final method incorporated sodium hydroxide (NaOH) combined with NaOCl to facilitate reduction of iodine in solution and enhance the NaOCl effect. The different methods were validated against an internal standard and the last method was chosen, as it showed the most reproducible and accurate results. As practical application, Iodine-129 concentration from both cores were compared, showing concentrations between 0.19 × 1012 at/kg and 7.16 × 1012 at/kg for core A and between 0.28 × 1012 at/kg and 2.40 × 1012 at/kg for core I. Despite the 129I diffusion detected in the deeper layers, depth profiles accurately reproduced Sellafield discharges, which is the nuclear fuel reprocessing plant closest to the cores., This work has been partially financed by the project PGC2018-094546-B-I00 by the Spanish Ministerio de Ciencia, Innovación y Universidades and the project US-1263369 by the Junta de Andalucía (Consejería de Economía y Conocimiento).

The Centro Nacional de Aceleradores is a user-oriented accelerator facility in Seville, Spain. Its main facilities are a 3 MV tandem accelerator, an 18 MeV proton Cyclotron, a tandetron used for AMS, a compact accelerator used for radiocarbon measurements, a 60Co irradiator and a PET/CT scanner. The technical specifications and research applications of these facilities are described. A neutron beam line associated to a charged pulsed beam in the tandem allows for time of flight measurements which determine the neutron energy. The use of an adequate stripper gas in the AMS tandetron permits to measure heavy radionuclides with very low detection levels, allowing to perform environmental studies using these radionuclides as tracers. The use of the microbeam in the tandem accelerator allows to apply the ion beam-induced current technique to investigate the spectroscopic properties and radiation hardness of different semiconductor detectors. European Union, H2020-847594, H2020-654002, H2020-847552, H2020-847594 Ministry of Science RTI2018-098117-B-C21, RTC-2017-6369-3, EQC2018-004193-P, EQC2018-004095-P, EQC2018-004166- P, PGC2018-094546-B-I00 Junta de Andalucía FEDER US-1261006, US-1263369, P18-RT-1900

Most of the anthropogenic radionuclide 129I released to the marine environment from the nuclear fuel reprocessing plants (NFRP) at Sellafield (England) and La Hague (France) is transported to the Arctic Ocean via the North Atlantic Current and the Norwegian Coastal Current. 129I concentrations in seawater provides a powerful and well-established radiotracer technique to provide information about the mechanisms which govern water mass transport in the Nordic Seas and the Arctic Ocean and is gaining importance when coupled with other tracers (e.g. CFC, 236U). In this work, 129I concentrations in surface and depth profiles from the Nordic Seas and the North Atlantic (NA) Ocean collected from four different cruises between 2011 and 2012 are presented. This work allowed us to i) update information on 129I concentrations in these areas, required for the accurate use of 129I as a tracer of water masses; and ii) investigate the formation of deep water currents in the eastern part of the Nordic Seas, by the analysis of 129I concentrations and temperature-salinity (T-S) diagrams from locations within the Greenland Sea Gyre. In the Nordic Seas, 129I concentrations in seawater are of the order of 109 at·kg− 1, one or two orders of magnitude higher than those measured at the NA Ocean, not so importantly affected by the releases from the NFRP. 129I concentrations of the order of 108 atoms·kg− 1 at the Ellet Line and the PAP suggest a direct contribution from the NFRP in the NA Ocean. An increase in the concentrations in the Nordic Seas between 2002 and 2012 has been detected, which agrees with the temporal evolution of the 129I liquid discharges from the NFRPs in years prior to this. Finally, 129I profile concentrations, 129I inventories and T-S diagrams suggest that deep water formation occurred in the easternmost area of the Nordic Seas during 2012., This work has been partially financed by the project FIS2015-69673-P by the Spanish Ministerio de Economía y Competitividad.

Parte del número especial: II International Conference on Radioecological Concentration Processes (50 years later) There are very few data available of 236U in marine sediment cores. In this study we present the results from the first oceanic depth profile of 236U in a sediment core sampled in the North Atlantic Ocean, at the PAP site (4500 m depth, Porcupine Abyssal Plain (PAP) site, 49°0′ N, 16°30′ W). Additionally, the sediment core was radiologically characterized through the measurement of anthropogenic 137Cs, 239Pu, 240Pu, 129I and 14C and natural 210Pb, 40K and 226Ra. The measured 236U concentrations decrease from about 90·106 at g−1 at the seafloor down to 0.5·106 at g−1 at 6 cm depth. They are several orders of magnitude lower than the reported values for soils from the Northern Hemisphere solely influenced by global fallout (i.e. from 2700·106 to 7500·106 at g−1). 236U/238U atom ratios measured are at least three orders of magnitude above the estimated level for the naturally occurring dissolved uranium. The obtained inventories are 1·1012 at m−2 for 236U, 80 Bq m−2 for 137Cs, 45 Bq m−2 for 239+240Pu and 2.6·1012 at m−2 for 129I. Atomic ratios for 236U/239Pu, 137Cs/236U and 129I/236U, obtained from the inventories are 0.036, 0.11 and 2.5 respectively. Concentration profiles show mobilization probably due to bioturbation from the abundant detritivore holothurian species living at the PAP site sea-floor. The range of 236U, 137Cs, 239+240Pu and 129I values, inventories and ratios of these anthropogenic radionuclides are more similar to the values due to fall-out than values from a contribution from the Nuclear Fuel Reprocessing Plants dispersed to the south-west of the North Atlantic Ocean. However, signs of an additional source are detected and might be associated to the nuclear wastes dumped on the Eastern North Atlantic Ocean. Ministerio de Economía, Industria y Competitividad FIS2015-69673-P

We present a detailed study of the performance parameters for 41Ca measurements at the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA) in Seville. Mixing CaF2 with Ag, we get stable (40CaF3)− currents between 50 and 100 nA. Transmission of the 2+ state in the He stripper is 41%, while optical transmission in the HE sector is typically higher than 95%. At low energies we cannot separate 41Ca from the isobar 41K at the detector, but the interference is reduced by using (41CaF3)− ions. The remaining contribution is corrected by measurement of the other stable isotope of potassium, 39K, to estimate this interference (K-correction). After this correction, we reach a 41Ca/40Ca background level between 5 × 10−12 and 8 × 10−12, making possible measurements of 41Ca/40Ca ratios higher than 4 × 10−11. Intercomparisons with the 0.6 MV AMS system at ETH Zurich show a quite good correlation. Ministerio de Economía y Competitividad FIS2015-69673-P

The Centro Nacional de Aceleradores (CNA) hosts a 1 MV accelerator mass spectrometry (AMS) apparatus since September 2005. In order to improve its overall performance, several updates have been made on the existing facility during the last 10 years of operation. In this paper, two modifications conducted in 2015 will be described. To increase the transmission of the ions through the accelerator, the stripping gas on the 1 MV CNA machine was changed from Ar to He. The measured maximum transmission for almost every isotope results to be higher, especially for heavy masses: for instance, in the case of uranium in the 3+ charge state, the transmission increased from 11% with Ar gas to about 38% with He gas. The second advance consisted of the substitution of the existing gas ionization chamber with a new one provided by ETH Zurich. The ETH detector features with its miniaturized design and is optimized for low energy AMS (i.e. very low electronic noise and efficient charge collection). As the electronic noise is the most important contribution to the resolution for light ions, the total energy resolution has been reduced by 15% in the case of 10Be, allowing a better discrimination against its isobar, 10B. For the heaviest radionuclides where the quality of the spectra is determined by the charge carrier production in the gas, the resolution for 2.7 MeV uranium ions was improved by 30%, probably due to a more efficient charge collection.

Measurements of 129I carried out on sea ice samples collected in the central Arctic Ocean in 2007 revealed relatively high levels in the range of 100–1400 × 107 at L−1 that are comparable to levels measured in the surface mixed layer of the ocean at the same time. The 129I/127I ratio in sea ice is much greater than that in the underlying water, indicating that the 129I inventory in sea ice cannot be supported by direct uptake from seawater or by iodine volatilization from proximal (nearby) oceanic regimes. Instead, it is proposed that most of the 129I inventory in the sea ice is derived from direct atmospheric transport from European nuclear fuel reprocessing plants at Sellafield and Cap La Hague. This hypothesis is supported by back trajectory simulations indicating that volume elements of air originating in the Sellafield/La Hague regions would have been present at arctic sampling stations coincident with sampling collection. Ministerio de Educación y Ciencia POL2006–00449

A quantitative evaluation of the fate of 129I, released from the European reprocessing plants of Sellafield (UK) and La Hague (France), has been made by means of a Lagrangian dispersion model. Transport of radionuclides to the Arctic Ocean has been determined. Thus, 5.1 and 16.6 TBq of 129I have been intro-duced in the Arctic from Sellafield and La Hague respectively from 1966 to 2012. These figures represent, respectively, 48% and 55% of the cumulative discharge to that time. Inventories in the North Atlantic, including shelf seas, are 4.4 and 13.8 TBq coming from Sellafield and La Hague respectively. These figures are significantly different from previous estimations based on field data. The distribution of these inven-tories among several shelf seas and regions has been evaluated as well. Mean ages of tracers have been finally obtained, making use of the age-averaging hypothesis. It has been found that mean ages for Sellafield releases are about 3.5 year larger than for La Hague releases. European Union FP7 EURATOM project PREPARE 323287 Ministerio de Ciencia, Innovación y Universidades FIS2012–31853

129I is a very long-lived radionuclide (T1/2 = 15.7 × 106 years) that is present in the environment both because of natural and anthropogenic sources. In this work 129I concentration and 129I/127I ratio have been determined in seaweed Fucus vesiculosus collected in the Southern Baltic Sea during 1982 and 1986 (post-Chernobyl accident). The resulting data were evaluated in terms of 129I concentrations, 129I/127I and 129I/137Cs ratios. 129I concentrations were found to be in the order of (0.82–5.89) × 109 atoms g−1 in 1982 and (1.33–38.83) × 109 atoms g−1 in 1986. The 129I/127I ratios ranged from (22.7–87.8) × 10−10 for seaweed collected in 1982 and from (26.1–305.5) × 10-10 for seaweed collected in 1986. Also a linear relationship was established for 127I concentrations in seawater and salinity in this area, enabling the estimation of concentration factors for 127I in F. vesiculosus. The high levels of 129I and 129I/127I in the Kattegat and their gradually decreasing trend to the Baltic Sea indicates that the most important contribution to the 129I inventory in the Baltic Sea area comes from Sellafield and La Hague reprocessing plants. With respect to Chernobyl accident, 129I concentrations in samples collected in 1986 were not much higher than those expected in less contaminated samples from 1982. This supports the view that the contribution of the Chernobyl accident to 129I in the Baltic region was not significant. Ministerio de Ciencia y Tecnología FIS2008-01149 Junta de Andalucía EXC/2005/RNM-419

129I is a very long-lived radionuclide (T1/2 = 15.7 × 106 years) that is present in the environment both because of natural and anthropogenic sources. In this work 129I concentration and 129I/129I ratio have been determined in rainwater samples collected at Seville (south-western Spain) during the period 2005–2008. Typical 129I concentration range from (0.26–8.86)×108 atoms/L, while 129I deposition are normally in the order of 107–108 atoms/m2d. Variability in the isotopic ratio 129I/129I indicates a range of (0.17–8.71) × 10−8. Temporal evolution of the 129I deposition seem to be related with the history of the 129I gaseous releases from the European reprocessing facilities at Sellafield and La Hague. The results obtained in this work are lower than the reported in previous works for the same location during the period 1996–1999, probably due to the reduction of the total gaseous 129I releases emitted by Sellafield and La Hague. The study of the dependence of the 129I deposition with some atmospheric parameters suggests that deposition seems to be more important in wet than in dry periods and that also depends in the wind direction, being more important for winds with north to south component. The agreement between the 129I concentration and the 129I/129I ratio suggest that the gaseous 129I emitted by the reprocessing plants has enough time to equilibrate with the 127I present in the atmosphere before arriving to southern Spain, probably due to the distance between Seville and these reprocessing plants. Ministerio de Ciencia y Tecnología FIS2008-01149 Junta de Andalucía EXC/2005/RNM-419

Desde que el Centro Nacional de Aceleradores (CNA) abriera sus puertas en 1997, los investigadores españoles cuentan con un laboratorio de referencia para estudiar la caracterización y modificación de materiales. Uno de los proyectos que allí se desarrollan consiste en medir isótopos radiactivos, lo que con las técnicas empleadas hasta ahora no se había conseguido. Se trata de un estudio en el que coopera Enresa, empresa con la que el CNA selló un convenio de colaboración en 2008, y cuyos resultados contribuirán a mejorar la seguridad en el almacenamiento de los residuos. Since the National Accelerators Centre (NAC) opened its doors in 1997, Spanish researchers have had use of a reference centre to study the characterisation and modification of materials. One of the projects developed there has been to measure radioactive isotopes that have not been measured using the techniques employed to da te. This study involves the cooperation of Enresa, with which the NAC established a collaboration agreement in 2008, and the results of which may help to improve the safe storage of waste.

La detección de radionúclidos de periodo de semidesintegración grande en muestras ambientales es interesante, entre otras razones, por la posibilidad que ofrece de trazar y comprender procesos naturales como mezclas de aguas marinas, tránsito de masas acuosas, intercambios atmosféricos verticales y horizontales, etc. Las condiciones necesarias, aunque no suficientes, para ellos son que Tn sea clar amente superior al tiempo medio de ocurrencia de la transformación ambiental problema y que el radionúclido sea conservatorio respecto a la misma. Es claro, pues, el interés que tiene el desarrollo de técnicas rigurosas y sensibles de determinación de radionúclidos en la naturaleza. La Memoria que presentamos consta de un Capítulo 2 en el que se hace una descripción general de la técnica de AMS. En el Capítulo 3 presentamos la instalación en la que se han realizado nuestras medidas: la instalación de AMS del Instituto de Física de Partículas de Zurich. El Capítulo 4 trata sobre el diseño y puesta a punto del sistema ideado para detección del 129I en esta instalación. En el Capítulo 5 se describen los métodos radioquímicos desarrollados para la separación de 129I de varios tipos de muestras naturales. Añadimos en el mismo capítulo información sobre los métodos de muestreo utilizados. Los resultados obtenidos y su interpretación se presentan en el Capítulo 6. Finalmente, las conclusiones extraídas en el trabajo se resumen en el Capítulo 7.

Universidad de Sevilla. Máster Universitario en Física Nuclear

Tesis llevada a cabo para conseguir el grado de Doctor por la Universidad de Sevilla--2018-09-28, The accelerator mass spectrometry (AMS) technique, developed 40 years ago for 14C dating, was soon used to measure other long-lived radionuclides. One of the radionuclides measured by AMS since these early years is 41Ca and for a variety of applications. Some of these applications are: the calculation of the terrestrial age of meteorites, the study of nuclear reactions of astrophysical interest, the understanding of the calcium metabolism, and the characterization of low-level nuclear waste. The main challenge in 41Ca AMS is dealing with the interference caused by its stable isobar, 41K. This interference is reduced by using calcium 2uoride (CaF2) samples and the extraction of the (CaF3)- ion. At large AMS facilities, besides, 41K ions can be discriminated from 41Ca ions using different detection techniques based on the energy loss dependence on the atomic number. The 41Ca measurement with low energy AMS systems, like the 1 MV system at the Centro Nacional de Aceleradores (CNA), is quite challenging, since this discrimination is not possible. Nevertheless, the 41K contribution can be estimated and, therefore, corrected, thanks to the sequential detection of the other stable isotope of potassium, 39K (K-correction). Although the sensitivity achieved in 41Ca AMS at low energies is 3-4 orders of magnitude lower than those achieved at larger facilities, it allows the competitive measurements for biomedical applications, and the characterization of concrete samples from nuclear reactor bioshields. Since 41Ca AMS at low energies is limited to the estimation of 41K interference, it is advisable to study the different ways toward the production of this interference. Some factors related to it have been studied in different experiments performed with the 1 MV AMS system at CNA (SARA) and the 600 kV AMS system at the ETH Laboratory of Ion Beam Physics in Zurich (TANDY). For instance, we could demonstrate that 41K can be injected also as the (41K57Fe)- molecular ion. As a consequence, 41K interference is dependent on the materials used during the sample pressing. We also proved that, even when both 41K/40Ca and 39K/40Ca ratios change over time, the relation between both, 41K/39K remains constant. Therefore, the Kcorrection is a robust method to estimate the 41K interference. The information provided from these experiments has contributed to the setting up and optimization of the 41Ca measurements with the SARA system at CNA, which was the main goal of this thesis. The results are not only useful for measurements at our system, but also for other very similar HVE 1 MV AMS systems. Several tests have been performed during these years to study and optimize all the performance parameters of 41Ca measurements with this system: ionization eWciency, transmission and destruction of the molecular background in the stripper, ion optical transport, detection eWciency, and 1nal sensitivity. Mixing the CaF2 samples with silver powder, our ion source produces stable (40CaF3)- currents between 50 and 150 nA. In comparison with the TANDY system at ETH, the slightly lower transmission for the 2+ state through the helium stripper (40% at SARA, 50% at TANDY) is compensated by the better optical transmission in the high energy sector (90-100% at SARA, 80-85% at TANDY). This is due to the quadrupole triplet which refocus the beam at the exit of our accelerator. The capabilities of both systems for 41Ca AMS are equivalent. 41Ca/40Ca backgrounds found in the system, in the 10-12 range, allow, among other applications, the characterization of the 41Ca content in the bioshield from nuclear reactors. Within the colaboration between the Spanish radioactive waste management agency (ENRESA) and the AMS Research group at CNA, a detailed study of the 41Ca spatial distribution in the bioshield of the Jos´e Cabrera nuclear power plant has been performed. A radiochemical method for concrete samples have been developed in order to deal with the relatively large number of samples involved in this study. The measured 41Ca/40Ca ratios in the areas of maximum neutron 2uence were on the 10-6 range, while they get down to the 10-10 range in regions far from the reactor cavity. While the 41Ca/40Ca attenuation pro1le follows an ideal behavior in some areas, it does not in other parts where the in2uence of diffused thermal neutrons is higher.

Falta palabras clave Los radionucleidos cosmogénicos de periodo de semidesintegración grande se encuentran en la naturaleza a niveles traza, lo cual hace que su medida sea realmente difícil. El hecho de que en la técnica de espectrometría de masas convencional sea muy difícil la discriminación entre el radionúclido que se desea medir y su interferente, hacía necesario el diseño y construcción de un nuevo sistema de espectrometría de masas que cumpliera con estas expectativas. La Espectrometría de Masas con Acelerador (AMS) es una técnica para la determinación de cantidades traza de radionúclidos de periodo de semidesintegración grande, en la que un acelerador de partículas generalmente electrostático de tipo tándem se acopla a un espectrómetro de masas que contiene los elementos convencionales para el transporte y la selección de iones en función de su masa y energía, de tipo magnético y electrostático. La concentración de los radionúclidos de interés se mide mediante la identificación y recuento de los iones con técnicas de detección nuclear que se pueden usar ya que los iones viajan a energías del orden del MeV/nucleón. La concentración del radionúclido problema se puede determinar, comparando el número de cuentas que llega al detector con la corriente de iones del núcleo estable, ya que en AMS la medida es de carácter relativo. Los principales atributos de la técnica estriban en la alta sensibilidad, casi una selectividad total y un amplio rango de medida de la concentración del radionúclido. El desarrollo del AMS ha aumentado la sensibilidad de detección en varios órdenes de magnitud con respecto al espectrómetro de masas convencional. Los interferentes isobáricos y moleculares, además, pueden ser separados casi completamente. En los años 70 comenzaron a instalarse los primeros espectrómetros de masas con acelerador tipo tándem, con la finalidad principal de la medida de 14C (T1/2= 5730 a), en pequeñas muestras con aplicaciones desde datación arqueológica a estudios de cambio climático. Pronto se vio su potencial para la utilización del sistema para otros radionúclidos, y aplicaciones tan diversas como la Física Nuclear Básica, Astrofísica, Ciencia de los Materiales, Biomedicina, Geología y todas las ciencias ambientales y paleoambientales; por lo que el uso de AMS se extendió a radionúclidos como 10Be (T1/2 = 1,51×106 a), 26Al (T1/2 = 7,17×105 a) y 36Cl (T1/2 = 3,01×105 a) y también isótopos pesados como 129I (T1/2 = 1,57×105 a), 239Pu (T1/2 = 24360 a), y otros radionúclidos de Pu. El alto coste de la técnica de AMS de alta energía (3-14 MV), ha impedido su implantación en muchos laboratorios a nivel mundial. A lo largo de estos años la evolución del AMS ha ido enfocada a la obtención de la máxima viabilidad de las medidas de estos radionúclidos, en sistemas de baja energía, es decir aquellos sistemas en los que la tensión de terminal del acelerador está sistemáticamente por debajo de 1 MV. En 1999 se diseña y construye, por parte del grupo de Física de Partículas del ETH de Zúrich, el primer AMS de Baja Energía (TANDY), con un voltaje del terminal de 600 kV y un área de 4,5×6,5 m2 , siendo el principio de este tipo de sistemas AMS. 2 En 2005 el Centro Nacional de Aceleradores (CNA), adquiere un sistema de Espectrometría de Masas con Acelerador de Baja Energía de 1 MV de voltaje de terminal denominado SARA (Spanish Accelerator for Radionuclides Analysis), desarrollado por la empresa High Voltage Engineering Europe (Amersfoort, Holanda), ocupando un área de 3.8×6.3 m2 . La adquisición de SARA ha permitido la implantación de la técnica de AMS en España mediante el desarrollo de distintas Tesis Doctorales sobre el uso de dicho sistema para las medidas de distintos radionúclidos en muestras de interés ambiental. Con esta Tesis completamos los estudios previamente hechos introduciéndonos en la medida de los radionúclidos 10Be y 26Al. El 10Be y 26Al son radionúclidos muy utilizados en diversas ciencias. El 10Be es una herramienta muy útil en geología y geocronología, ya que es un trazador muy importante en la tierra. Es utilizado para el conocimiento en el modelado y transformación de paisajes, en estudios de variaciones del clima, cambios en el flujo la radiación cósmica, datación de rocas (junto a 26Al), tasas de erosión y denudación en superficies y sedimentos, estudio de su producción en la atmósfera y en superficies y su posterior distribución, en estudios del reciclado de sedimentos en volcanes y también en residuos de la industria nuclear. Por otra parte, debido a su producción en la tierra, el 26Al es también utilizado para la datación de rocas y sedimentos y en la datación de superficies junto a 10Be y en estudio de rocas lunares y meteoritos. Además, en las últimas décadas, el 26Al se utiliza en Biomedicina, ya que se utiliza como trazador en el metabolismo de seres vivos. Estudios de su absorción por riñones y cerebro ha conllevado su uso en investigación de enfermedades como disfunciones renales o incluso la enfermedad de Alzheimer. La importancia de estos dos radionúclidos requería de su estudio y aprendizaje en el Centro Nacional de Aceleradores. Anteriormente, en las instalaciones del CNA se probó la capacidad del AMS de baja energía para detectar 26Al en los test de aceptación que se llevaron a cabo después de su instalación. Hasta ahora, sin embargo, con esta Tesis se ha llevado a cabo el trabajo de optimización de las medidas de 26Al en el sistema y el desarrollo de la radioquímica asociada para el aislamiento y obtención de ambos radionúclidos en diferentes tipos de muestras. Estos puntos son los objetivos principales de esta Tesis Doctoral. Con la obtención de estos conocimientos se contribuirá la apertura de nuevas líneas de investigación tanto del grupo de Física Nuclear Aplicada como en el CNA y a su vez, a tener la posibilidad de realizar medidas rutinarias, de sendos radionúclidos, de otros grupos de investigación en el Centro Nacional de Aceleradores. El desarrollo de esta Tesis Doctoral se muestra en esta memoria dividida en 6 capítulos. En el capítulo 2, se realiza un esbozo de una de las primeras preguntas que nos podemos realizar al leer las líneas anteriores. ¿Qué es un sistema de Espectrometría de Masas con Acelerador? En este capítulo se realiza una disertación de los elementos del sistema y funcionamiento de este tipo de sistemas y posteriormente una descripción del sistema de AMS del Centro Nacional de Aceleradores de Sevilla (SARA), dividiendo el relato en tres partes: zona de baja energía, acelerador y zona de alta energía, en el que se describen los elementos y lentes que conforman el sistema. La producción de 10Be y 26Al en la tierra es similar. Los rayos cósmicos inciden en la tierra produciéndose reacciones nucleares de espalación, en la atmósfera (10Be y 26Al “meteórico”) y en la superficie de la tierra, concretamente en cuarzo (10Be y 26Al “in situ”). En el capítulo 3 se 3 realiza una descripción de la producción y distribución de ambos radionúclidos en la tierra, y sus aplicaciones en diferentes ciencias. En el capítulo 4 se realiza una descripción detallada del trabajo realizado para llevar a cabo la optimización del sistema para la medida de 26Al, consistiendo en la obtención de la transmisión del haz después del proceso de stripping, las medidas de diferentes estándares para la obtención de la recta de calibrado y las medidas de los valores de fondo, para los estados de carga +1 y +3. A su vez se ha realizado un estudio de la variación de la corriente respecto a la matriz de metal y su concentración, con la que se mezcla la muestra y comparación con TANDY. Posteriormente se describen los procesos radioquímicos utilizados para la determinación de las concentraciones de 10Be y 26Al en diferentes tipos de muestra, dependiendo de si el radionúclido ha sido producido en la atmósfera (meteórico) o en la superficie (in situ). Finalmente se realizan estudios de variación de la corriente obtenida dependiendo de la temperatura de calcinación de Al(OH)3 a Al2O3 y del efecto en la corriente del uso de coprecipitantes en la obtención de Al(OH)3, comparando los sistemas SARA Y TANDY. En el capítulo 5 se realizan la determinación de las concentraciones de 26Al y 10Be, en diversos tipos de muestra. Por ejemplo, en muestras de cuarzo las concentraciones medidas en SARA son comparadas por las ya obtenidas por el laboratorio SUERC en las mismas. En este tipo de muestras, nos centraremos en la implantación y optimización del proceso radioquímico en nuestro laboratorio. El 26Al en la atmósfera no está muy estudiado, por lo que con el objetivo de aportar nuevos datos sobre 26Al y 10Be, se han extraído sendos radionúclidos de filtros de aerosoles atmosféricos, ofreciendo sus ratios y concentraciones en una estación a nivel del mar, medias latitudes y en la ciudad de Sevilla y su correlación con las condiciones climáticas. El 10Be meteórico se mide en muestras de sedimentos del río Guadiana, con cuyos resultados obtendremos la tasa de denudación (erosión), en el estuario y será comparado con la tasa de denudación obtenida por el método del balance de sedimentos. Con respecto a la industria nuclear, se ha determinado 10Be en muestras de resinas intercambiadoras de iones de centrales nucleares, por las que se han hecho pasar aguas residuales de este tipo de industrias, obteniendo las concentraciones de este radioisótopo adsorbido por las resinas. A su vez, también se han tratado muestras de dawsonitas e hidrotalcitas, para comprobar la capacidad de estos tipos de materiales para la adsorción selectiva de 10Be en aguas residuales de una central nuclear. Las muestras de dawsonitas e hidrotalcitas y resinas fueron aportadas por ENRESA. En este mismo capítulo se hace una descripción del estudio sobre el 10Be reciclado de los sedimentos del fondo marino que han erupcionado en diversos volcanes en la cordillera de los Andes, midiendo 10Be en las muestras de cenizas volcánicas en el sistema SARA del Centro Nacional de Aceleradores. Finalmente en el capítulo 6 se exponen las conclusiones obtenidas en el trabajo realizado en la optimización de 26Al y las medidas realizadas para ambos isótopos en los distintos tipos de muestras analizadas. Cosmogenic radionuclides with long half-life are located in the nature at trace levels, therefore, their measurement is really difficult. Being that the conventional Mass Spectrometry is not able to distinguish between the radionuclide and its isobar, the design and the setting up of a new system was needed. Accelerator Mass Spectrometry (AMS) is a technique adopted to measure radionuclides with a large half-life at trace levels, where a tandem electrostatic particles accelerator is coupled to a mass spectrometer, which has magnetics and electrics elements to carry and select the ions by mass and energy. Isotopes are identified and counted with nuclear detection techniques, which can be used because the ions' energy is around 1 MeV/nucleon. The concentration of the problem isotope can be determined comparing the counts which are reaching the detector with the stable ions current, because the measurement has a relative character in AMS. The main features of the technique are the high sensitivity, almost a total selectivity and a great range of measurement of the isotope concentration. The development of the AMS has increased the detection sensitivity of several orders of magnitude with respect to the conventional Mass Spectrometry. Furthermore, the isobar and molecular interference can be separated almost totally. The first tandem accelerator mass spectrometers began to be installed during the 70's with the main aim of 14C measurement (T1/2= 5730 y) in small samples, with applications in archaeological dating or climatic changes studies. It was quickly checked the great potential of such a system to the measurement of other radionuclides and other applications like Basic Nuclear Physics, Astrophysics, Material Sciences, Biomedicine, Geology, Environmental and Palaoenvironmental Sciences; therefore the use of the AMS was extended to both the light radionuclides such as 10Be (T1/2 = 1,51×106 y), 26Al (T1/2 = 7,17×105 y) and 36Cl (T1/2 = 3,01×105 a) and the heavier ones like 129I (T1/2 = 1,57×105 a), 239Pu (T1/2 = 24360 a) and other Pu’s isotopes. The high cost of High Energy AMS technique (3-14 MV) stopped its setting up in laboratories around the world. Over the years, the evolution of the AMS has been focused on the viability of radionuclides measurements in low energy systems, whose terminal voltage is lower than 1 MV. In 1999, the Particle Physics group of ETH Zürich designed and built up the first Low Energy AMS (TANDY), with a terminal voltage of 600 kV and an area of 4,5×6,5 m2 , being the beginning of this kind of systems. In 2005, the Accelerators National Center (CNA) in Seville purchased a Low Energy AMS system built by High Voltage Engineering Europe, with 1 MV terminal voltage and a 3.8×6.3 m2 area named SARA (Spanish Accelerator for Radionuclides Analysis). SARA installation has allowed the implantation of the AMS technique in Spain through the development of several Doctoral Thesis centered on the use of the system for the measurements 5 of distinct radionuclides in environmental samples. With this thesis, the studies which has been performed so far are completed, introducing the measurements of 26Al and 10Be radionuclides. Both 10Be and 26Al find application fields in several Sciences. 10Be is a powerful tool very used in Geology and Geochronology, because it’s a very important tracer on the Earth. It’s used to investigate the shaping and the transformations of landscapes, weather variations, changes in the cosmic rays flux, rocks dating (together with 26Al), the erosion and denudation rates in surfaces and sediments, its productions in the atmosphere and subsequent distribution, recycled sediments by volcanos and wastes of nuclear powers facilities. On the other hand, because of its production on the Earth, the 26Al is used on rocks, sediment and surfaces dating as well as 10Be and on meteorite and lunar rocks. During the last decades, the 26Al started being adopted in Biomedicine as a tracer in living organisms’ metabolism. Studies about its absorption in kidneys and brain led to use it in researches concerning sicknesses as the Alzheimer. Due to the importance of both radionuclides, specific studies had to be carried on at the National Accelerator Centre. First of all, the capacity of Low Energy AMS to detect 26Al was tried on the acceptation tests, which were carried out after the setting up. With this thesis, the work related to the optimization of 26Al measurements and to the development of the associated radiochemistry needed to isolate and take the two radionuclides off from different samples has been made. Those points are the main aims of this thesis. Thanks to the acquired abilities and having the possibility to make routine measurements to both radionuclides, new research lines will be opened for the Applied Nuclear Physics group, for the National Accelerators Centre and for other research groups at the National Accelerators Centre. In this thesis, the optimization of the system for 26Al measurements has been realized studying the transmission of the beam along the stripper, measuring the correlation curve for several standards and evaluating the background level against the stripper pressure in blanks for both charge states +1 and +3. A study about the variation of the current over the metal matrix and its concentration have been performed and compared with the same test at the TANDY. The radiochemical procedures have been adapted in our laboratory to meteoric and in situ 26Al and 10Be radionuclides in quartz and sediments. In addition, a new radiochemical procedure is described for measurement of both 26Al and 10Be in aerosol filters. To complete the radiochemical procedure, studies about the variation of the current against the calcination temperature of Al2O3 and the use of Fe, to coprecipitate the Al(OH)3 have been done. The ratios 26Al/27Al, 10Be/9 Be and the concentrations of 26Al and 10Be have been measured in quartz samples of rocks and sediments of terraces. Those samples were early measured at SUERC and the results were compared with our ones, being consistent between them for ratios and concentrations for 26Al and 10Be. 26Al in the atmosphere doesn’t have been so studied; thus, 26Al and 10Be were extracted from aerosols filters in Seville city, with the aim to provide new data about the concentrations of both radionuclides and the ratio 26Al/10Be. The results were one order of magnitude higher than what can be found in the literature, showing the presence of an extra contribution for 26Al from other places near Seville. 26Al and 10Be are currently measured in aerosol filters in Antarctic, high latitudes, high altitudes, in lower stratosphere or upper troposphere. The measured aerosol filters were collected at sea level, midlatitudes and down town. 10Be meteoric was measured on sediments samples from Guadiana River, with the aim to get the denudation rate of the basin of the river. The datum was compared with the one obtained by the sediment budget method which is a twofold higher than our result. Concerning the waste 6 of nuclear powers, it’s important to know the radionuclides which are in the wastes to provide a right store of them. At the CNA, 10Be has been measured in resins exchange ions, to know the amount of 10Be in the reactor and the store pool water. Dawsonites and Hidrotalcites are selective absorbers of cations and anions. They have been measured to try their capability of absorbing 10Be from waters of nuclear powers. Finally, it will be done a description of the study of recycled 10Be from sediments under the sea which are eruptioned from volcanos in the Andes, measuring 10Be in volcanos ashes samples in SARA system at National Accelerators Centre.

La Memoria que desarrollamos a continuación consta de seis capítulo, cuyo contenido se discute a continuación. En el Capítulo 2 se hace una descripción general de la técnica de AMS y una caracterización del sistema compacto de AMS del CNA (SARA, Spanish Accelerator for Radionuclides Analysis), instalación en la que se han obtenido los resultados que se presentan en esta Tesis. En el Capítulo 3 se muestra el diseño de la óptica de iones del sistema SARA, o forma en la que el haz de partículas es transportado desde la fuente de iones hasta el detector, y la puesta a punto del mismo para la detección de 129I. En este Capítulo encontramos las simulaciones realizadas para reproducir el comportamiento óptico del sistema y todos los experimentos llevados a cabo para optimizar los parámetros que hacen posible la medida de 129I en el sistema de AMS del CNA. El Capítulo 4 comienza con una reseña acerca de la presencia del yodo en la naturaleza, su distribución en los distintos compartimentos naturales y las distintas fuentes de producción de 129I, y sigue con una descripción del método radioquímico desarrollado para su extracción de muestras sólidas. Las aplicaciones medioambientales se muestran en el Capítulo 5, en el que abordaremos el problema de la medida de 129I en varios tipos de muestras ambientales, como son líquenes, algas y turbas. Concluiremos el trabajo con el Capítulo 6, en el que presentaremos un resumen de la labor realizada y de los resultados más relevantes obtenidos en este trabajo.Posteriormente al Capítulo 6 existe un Anexo en el que se pormenoriza el experimento realizado con la técnica de XRF (Fluorescencia de Rayos X) y que concluyó con la obtención de los resultados preliminares referentes al rendimiento del método radioquímico que se muestran en el Capítulo 4.De modo general, podemos decir que con la realización de este trabajo se ha conseguido un importante avance en la detección de 129I mediante AMS. Estas mejoras se han producido en tres aspectos diferentes. En primer lugar físico, con la puesta a punto del nuevo sistema compacto de AMS del CNA, el primero multielemental fabricado por HVEE y la única instalación de AMS en España para la medida de 129I. En segundo lugar se han producido avances desde el punto de vista radioquímico, poniendo a punto un método de preparación de muestras que introduce mejoras respecto al que se venía utilizando en este grupo de investigación. Por último, se han aportado nuevos datos acerca de la presencia de 129I en el medioambiente. A partir del análisis de la presencia de 129I en líquenes, algas y turbas se han podido extraer algunas conclusiones acerca del origen y comportamiento ambiental de este radionúclido.