The goal of this research was to devise a new analytical technique, using Accelerator Mass Spectrometry (AMS), to measure Platinum Group Element (PGE) concentrations to the sup-ppb levels in natural, insulating, samples. The challenges were threefold. First, a method of sputtering an insulating sample to successfully produce a stable beam of anions needed to be devised. Second, a suitable standard of known PGE concentrations had to be found and third, spectral analysis of the beam had to verify any claims of PGE abundance. The first challenge was met by employing a modified high intensity negative ion source flooded with neutral caesium that successfully sputtered insulators to produce a beam of negative ions. The second challenge, that of finding a suitable standard, was fraught with difficulties, as no synthesized standards available were found to be appropriate for this work. As a result, direction is provided for future production of standards by ion implantation. The third challenge, successful spectral analysis, was accomplished using a newly designed gas ionization detector which allowed for resolution of the interfering molecular fragment from the PGE ions. Coupled with the use of the SRIM computer programme, positive identification of all peaks in the spectra of the analyzed samples was accomplished. The success of the first and third challenges lead to the qualitative analyses of geological samples for sub-ppb levels of PGE by AMS. Quantitative analyses await only for the appropriate standards and with those will come a whole new range of research possibilities for measuring sub-ppb levels of PGE in insulating samples by AMS.

The development of an accurate and precise geochronology is imperative to understanding archives containing information about Earth’s past. Unable to date all intervals of an archive, researchers use methods of interpolation to approximate age between dates. Sections of the radiocarbon calibration curve can induce larger chronological uncertainty independent of instrumental precision, meaning even a precise date may carry inflated error in its calibration to a calendar age. Methods of interpolation range from step-wise linear regression to, most recently, Bayesian statistical models. These employ prior knowledge of accumulation rate to provide a more informed interpolation between neighboring dates. This study uses a Bayesian statistical accumulation model to inform non-sequential dating of a sediment core using a high-throughput gas-accepting accelerator mass spectrometer. Chronological uncertainty was iteratively improved but approached an asymptote due to a blend of calibration uncertainty, instrument error and sampling frequency. This novel method resulted in a superior chronology when compared to a traditional sediment core chronology with fewer, but more precise, dates from the same location. The high-resolution chronology was constructed for a gravity core from the Pigmy Basin with an overall 95% confidence age range of 360 years, unmatched by the previously established chronology of 460 years. This research reveals that a larger number of low-precision dates requires less interpolation, resulting in a more robust chronology than one based on fewer high-precision measurements necessitating a higher degree of age interpolation.

Iodine-129 is a naturally and anthropogenically produced radioisotope (half-life: 15.7 million years) the majority of which is produced by nuclear fuel reprocessing. These releases have dispersed 129I throughout the environment making it possible to use 129I as a tracer. It is also of concern for the disposal of radioactive waste. This research develops a new laboratory method for 129I extraction and analysis, and explores the geochemical cycling and environmental fate of 129I in remote catchments following the Fukushima-Daiichi Nuclear Accident (FDNA). A new technique was developed to investigate 129I partitioning and quantitatively extract it from solid samples. Samples are combusted and volatilized iodine is trapped in solution. The efficiency is traced using the iodine isotope, 125I. This technique was proven using standard reference materials and is used in other chapters of this thesis. A baseline study of 129I in Yukon watersheds was undertaken to determine the impact of anthropogenic 129I emissions and identify possible sources. Using atmospheric back-trajectory modeling, sources of 129I from Fukushima, nuclear fuel reprocessing and marine volatilization were identified in remote watersheds. Peat moss samples showed significant retention of 129I in modern samples. Following the reconnaissance study, a catchment scale investigation of anthropogenic 129I cycling was undertaken through precipitation and runoff monitoring. 129I was found to be an excellent indicator of initial snowmelt contributions to discharge due to enrichment by dry deposition. Furthermore, water source transitions in discharge were recorded by 129I, 127I and the 129I/127I ratio showing iodine can be used as a tracer of hydrologic processes. A mass balance found that 77% of the 129I mass input accumulates annually, primarily in organic soils. Sampling of Vancouver, B.C. precipitation and groundwater was done following the FDNA to determine the fate of 129I and evaluate it as a tracer of groundwater recharge. Immediately following the FDNA the 129I concentration in precipitation increased 6 times above background. Groundwater samples also showed 129I increases consistent with expected recharge times indicating FDNA derived 129I was transported into groundwater with minimal retardation, likely via preferential flowpaths.

Accelerator Mass Spectrometry (AMS) studies of rare isotopes with abundant isobars that form negative ions often require the use of large accelerators to achieve high sensitivity measurements. The Isobar Separator for Anions (ISA) is a radiofrequency quadrupole (RFQ) reaction cell system that provides selective isobar suppression for many of these isotopes in the low energy system, prior to injection into an accelerator. The ISA can then facilitate the measurement of these ions using smaller accelerators. A commercial version from Isobarex Corp. was installed in a separate low energy injection line of the 3 MV accelerator system at the A. E. Lalonde AMS Laboratory in the University of Ottawa and was tested using the measurement of 36Cl, suppressing its stable isobar 36S. The ISA includes a DC deceleration region, a combined cooling and reaction cell, and a DC acceleration region. The deceleration region reduces the beam energy from the ion source (20-35 keV) to a level that chemical reactions can occur, scattering is minimized, and that the reaction cell can accept and contain. RFQ segments along the length of the cell create a potential well, which limits the divergence of the traversing ions. DC offset voltages on these RFQ segments maintain a controlled ion velocity through the cell. Helium was used as a cooling gas to further decelerate the ions, facilitating charge exchange between 36S and a reaction gas. Helium provided the highest transmission of 30-80% for chlorine anions. The reaction gas NO2 was chosen to preferentially react with sulfur. Over seven orders of magnitude reduction of sulfur to chlorine was observed. After exiting the cell, the beam is reaccelerated prior to injection into the tandem accelerator for AMS analysis. Using 36Cl reference materials, it was determined that linear transmission results could be obtained for a 36Cl/Cl ratio ranging from 10−11 to 10−15. The measurements were stable over more than 24 hours of continuous measurement. A blank level on the order of 10−15 was observed. The ISA was used to measure unknown 36Cl /Cl ratio groundwater samples and the results are compared to external AMS measurements.

Since the beginning of the nuclear era, starting during the 1940s, large amount of radioactivity has been released into the environment. This thesis deals with the temporal and spatial distribution of the anthropogenic radioisotope 129I (T1/2= 15.7 Myr) in northern Europe. A routine sample preparation procedure for extraction of iodine from milligram amounts of solid materials has been developed and aimed for measuring the 129I concentration by the ultra-sensitive accelerator mass spectrometry method. The technique was further used for the analysis of 129I in sediments collected from two lakes in Sweden and one lake in Finland as well as sediments from two sites in the Baltic Sea. In addition, 129I concentrations in aerosol samples from northern and southern Sweden covering the period 1983 to 2000 have been measured. The results reveal a gradual increase in the anthropogenic 129I fluxes since the 1950s that are linked to emissions from the nuclear fuel reprocessing facilities in Sellafield (UK) and La Hague (France). A sharp increase coinciding with the Chernobyl accident is identified from the Swedish lakes located in areas characterised by relatively high Chernobyl fallout. Numerical modeling of the 129I deposition predicts that >50% of the flux to the lake sediments is related to the liquid emissions from the reprocessing facilities. The modeling also reasonably simulates the contribution of the Chernobyl event to the total 129I flux. The novel time series from northern Europe on 129I in aerosols show about one order of magnitude higher concentration in northern compared to southern Sweden. Estimate of 129I dry fallout based on the aerosol data suggests <25% contribution to the total fallout. The distribution of 129I in the sediment archives demonstrates the potential of the isotope as a new time marker for chronological and environmental investigations.

Submitted by Biblioteca do Instituto de Física (bif@ndc.uff.br) on 2017-06-09T19:40:00Z No. of bitstreams: 1 DissertacaoMestrado_FabianaMonteiro.pdf: 63170351 bytes, checksum: c19ab17f1c6a5a21e7a5a6ed4744c86e (MD5) / Made available in DSpace on 2017-06-09T19:40:00Z (GMT). No. of bitstreams: 1 DissertacaoMestrado_FabianaMonteiro.pdf: 63170351 bytes, checksum: c19ab17f1c6a5a21e7a5a6ed4744c86e (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Durante os últimos 1000 anos ocorreram significativas mudanças climáticas em nosso planeta, que tem sido caracterizada como uma Pequena Idade do Gelo (LIA). Este foi um período de esfriamento global, que ocorreu após o Período Quente Medieval, estendendo-se entre os séculos XIV e XIX, aproximadamente de 1350 a 1850. A compreensão deste fenômeno, relacionado a mudanças globais, possui grande interesse científico. No Hemisfério Norte há vários trabalhos científicos que relacionam os resultados encontrados com a Pequena Idade do Gelo e o Período Quente Medieval, já no Hemisfério Sul esses eventos são incertos devido a escassez de material datado dessa época. Isto tem provocado uma grande controvérsia, uma vez que embora alguns dos poucos trabalhos existentes tenham identificado que o mesmo período de resfriamento também tenha ocorrido na América do Sul, outros autores discordam que esse período frio possa ser aplicado globalmente. Desta forma, ainda há uma questão em aberto, onde trabalhos que exploram a reconstrução de encostas (superfície do mar), vazão de rios e a produtividade biológica sul americanas, podem contribuir na elucidação deste problema. Dentro deste contexto, esta dissertação propôs uma contribuição no estudo da formação de encostas brasileiras, mais especificamente, na enseada do Pântano Sul, Ilha de Santa Catarina, SC, onde testemunhos sedimentares demonstraram uma variação significativa na composição de seus sedimentos, que podem estar associados a eventos de mudanças climáticas significativas. Para tanto, foi utilizada a técnica de AMS (Accelerator Mass Spectrometry), através da datação de radiocarbono de amostras de conchas e sedimentos, oriundas destes testemunhos sedimentares, numa colaboração entre pesquisadores do Instituto de Física e Departamento de Biologia Marinha, ambos da Universidade Federal Fluminense (UFF). Em adição, esta dissertação apresenta um grande destaque como marco tecnológico, pois é o primeiro trabalho aplicando a técnica AMS, desenvolvida integralmente em um país Latino-Americano. Assim, são apresentados os primeiros resultados para a utilização de um acelerador do tipo SSAMS (Single Stage Accelerator Mass Spectrometry System) de 250kV, recém instalado no Instituto de Física da UFF. Desta forma, a técnica de datação 14C-AMS já pode ser totalmente realizada aqui no Brasil e na América Latina. / During the last 1000 years significant climatic changes have occured in our planet, which have been characterized as a Little Ice Age (LIA). This was a period of global coldness, after the Warm Medieval Period, between the XIV and XIX centuries, aproximately from 1350 to 1850. The understandind of such fenomenum, related to global changes, is of great scientifc interest. In the northern hemisphere there are many works relating its results to the Little Ice Age and the Warm Medieval Period. In the southern hemisphere however, these events are not clear due the lack of events. This has lead to controversy since a few works have identifyed the same cold period in South America, others authors disagree that it was a global phenomenum. This way, there is still an open question, where studies that explores coastal reconsctruction (ocean surface), river flow and the biological productivity in South America can contribute to solving the problem. in this sence, this work proposes a contribution to the study of Brazilian coastal formation, more specifically in the Pantano Sul Inlet, Santa Catarina Island, SC, where sediment cores have shown a significant climatic changes. In this study, we used the Accelerator Mass Spectrometry (AMS) thecniche, for the radiocarbon dating of shells and sediment from the collected cores in a collaborative work between researches from the Physics Institute and the department of Marine Biology, both from the Fluminense Federal University. In addition, this work is a technological mark since it is the first results of Single Stage Mass Spectrometry Accelerator System, recently installed in the Physics Institute of UFF. Therefore, the 14C-AMS dating technique can now be throroughly permormed in Brazil and Latin America.

¹⁴C wiggle-matching was applied to two wood samples closely related to geological and archaeological events with associated dendrochronological dates, to demonstrate the accuracy of ¹⁴C dating with accelerator mass spectrometry (AMS). Wiggle-matching on charred wood with bark, excavated from a pyroclastic mud-flow deposited by the huge 10th Century eruption of the Baitoushan Volcano, revealed the eruption age as cal A.D. 935 +8/-5 with 95% confidence. This date is consistent with the eruption age of A.D. 912 to A.D. 972 estimated by dendrochronology on two wooden boards that had clear stratigraphical connections to the B-Tm tephra deposit in Japan, an ash fall layer formed by the eruption of the Baitoushan Volcano. The date is also consistent with an A.D. 937–938 date estimated by the analysis of varved sediments from Lake Ogawarako in Aomori prefecture. The other wooden board collected from the Mawaki archaeological site in Ishikawa prefecture was wiggle-matched as 783 +13/-11 cal B.C. with 95% confidence, which is consistent with the dates of 830 cal B.C. to 759 cal B.C. obtained for seven wooden poles from the same wooden structures as the wooden board. These results are highly encouraging for obtaining accurate dates on wood when dendrochronology cannot be used.

La détermination de la concentration des RadioNucléides à Vie Longue (RNVL) dans les déchets de l'industrie nucléaire est essentielle pour la gestion sur le long terme des sites de stockages. Cette étude se focalise sur la détermination de la concentration de trois RNVL : 129I, 41Ca et 10Be dans les résines échangeuses d'ions utilisées pour la purification du fluide primaire des Réacteurs à Eau Pressurisée (REP). Afin d'exploiter les potentialités de la Spectrométrie de Masse par Accélérateur (SMA) pour mesurer ces radionucléides présents en de très faibles concentrations, des procédures analytiques spécifiques ont été développées incluant : 1) la minéralisation des échantillons, 2) l'extraction sélective des analytes, 3) le conditionnement pour la mesure par SMA. Appliquées à des échantillons de résines usées provenant d'une centrale EDF (REP 900 MWe), les procédures développées ont permis l'extraction quantitative et sélective des RNVL d'intérêt vis-à-vis des émetteurs β-γ et des isobares avant leur mesure par SMA sur l'instrument national ASTER (CEREGE, Aix-en-Provence). L'iode 129, le calcium 41 et le béryllium 10 ont été mesurés dans les résines usées à des concentrations de l'ordre de 10 ng/g, 20 pg/g et 4 ng/g de résine sèche, respectivement. Pour ce qui concerne l'iode 129 et le calcium 41, ces concentrations sont en accord avec celles estimées à partir de facteurs de corrélation établis relativement à des émetteurs gamma facilement mesurables (137Cs et 60Co). Dans le cas du béryllium 10, les résultats obtenus différent significativement des valeurs attendues mais sont cohérents avec de précédentes mesures réalisées par ICP-MS. / Determining the concentration of Long-Lived RadioNuclides (LLRN) in nuclear waste is fundamental for the long term management of storage sites. This study focuses on the determination of three LLRN concentrations, i.e. 129I, 41Ca and 10Be, in ion exchange resins used for primary fluid purification in Pressurized Water Reactors (PWR). To benefit from the Accelerator Mass Spectrometry (AMS) technique allowing to measure extremely low levels of nuclide concentrations, analytical procedures including: 1) sample dissolution; 2) selective and quantitative extraction of the analyte; and, 3) analyte conditioning for AMS measurements, were developed. Applied on spent resin samples collected at a 900 MW PWR, the procedures developed for each studied LLRN allowed their quantitative recovery and their selective extraction from β-γ emitters and isobars. The concentration measurements of the LLRN of interest were then performed on the Accelerator Mass Spectrometry national facility ASTER housed by the Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement (CEREGE, Aix-en-Provence). 129I, 41Ca and 10Be concentrations in spent resins were measured to be about 10 ng/g, 20 pg/g and 4 ng/g of dry resin, respectively. Considering 129I and 41Ca, the measured concentrations agree with those assessed from scaling factors established relatively to easily measured gamma emitters (137Cs and 60Co). For 10Be, the presented results are significantly different from expected values but are in agreement with previous ICP-MS results.

Two long-lived halogen radionuclides (36Cl, T1/2 = 301 kyr, and 129I, T1/2 = 15.7 Myr) have been studied by means of Accelerator Mass Spectrometry (AMS) at the Uppsala Tandem Laboratory. The 36Cl measurements in natural samples using a medium-sized tandem accelerator (~1 MeV/amu) have been considered. A gas-filled magnetic spectrometer (GFM) was proposed for the separation of 36Cl from its isobar, 36S. Semi-empirical Monte-Carlo ion optical calculations were conducted to define optimal conditions for separating 36Cl and 36S. A 180° GFM was constructed and installed at the dedicated AMS beam line. 129I has been measured in waters from the Arctic and North Atlantic Oceans. Most of the 129I currently present in the Earth's surface environment can be traced back to liquid and gaseous releases from the nuclear reprocessing facilities at Sellafield (UK) and La Hague (France). The anthropogenic 129I inventory in the central Arctic Ocean was found to increase proportionally to the integrated 129I releases from these reprocessing facilities. The interaction and origin of water masses in the region have been clearly distinguished with the help of 129I labeling. Predictions based on a compartment model calculation showed that the Atlantic Ocean and deep Arctic Ocean are the major sinks for the reprocessed 129I. The variability in 129I concentration measured in seawater along a transect from the Baltic Sea to the North Atlantic suggests strong enrichment in the Skagerrak–Kattegat basin. The 129I inventory in the Baltic and Bothnian Seas is equal to ~0.3% of the total liquid releases from the reprocessing facilities. A lake sediment core sampled in northeastern Ireland was analyzed for 129I to study the history of the Sellafield releases, in particular the nuclear accident of 1957. High 129I concentration was observed corresponding to 1990 and later, while no indication of the accident was found. The results of this thesis research clearly demonstrate the uniqueness and future potential of 129I as a tracer of processes in both marine and continental archives.

207Pb*/206Pb* chronometry was used to obtain the ages of Ca,Al-rich inclusions (CAIs) and chondrules found in ancient meteorites. Assuming a 238U/235U=137.88, Pb/Pb ages of chondrules in NWA801 (a CR2 meteorite) are 4564.6±1.0 Ma, chondrules in Mokoia (a CV3 chondrite) are 4564.2±1.1Ma, and CAIs in Mokoia are 4567.9±5.4 Ma. The Pb/Pb age of NWA801 chondrules is concordant with 26Al/26Mg ages of CR chondrules. However if a 238U/235U < 137.88 is used, the age for NWA801 chondrules becomes younger by ~1Ma and discordant with 26Al/26Mg ages of CR chondrules. This suggests either a discrepancy with the U compositions or the initial Mg isotopic compositions of NWA801 chondrules. The shapes of NWA801 chondrules, and blebs of FeNi metal in the meteorite matrix, were further studied by 3D X-ray micro-computed tomography (CT). Most chondrules (92%) were ‘armoured’ with one discontinuous layer of FeNi metal. Two layers of FeNi metal (one on the exterior and one concentric through the interior separated by silicate) were rare <8%. Chondrules and matrix blebs occur as oblates, prolate, spheres and triaxial spheroids. It is proposed that the shapes were made free-floating in the nebula likely by flash-melting precursors into molten droplets that were vibrating as harmonic oscillators that ‘froze-in’ their shapes during cooling. Parent-body metamorphism and shock are not likely processes affecting the matrix-bleb and chondrule shapes. Chondrules with ≥2 FeNi metal layers were likely formed by mergers and not by successive deposition and annealing of metal in multiple flash-melting events. Attempts to obtain 207Pb*/206Pb* ages from chondrules and CAIs by thermal extraction (TE)- TIMS were unsuccessful. However LA-ICP-MS was shown to be useful for rapidly determining Pb isotopic trends in meteorites and unknown objects. In particular, it was shown that 137La (T1/2=60ky) should be detectable in recently fallen meteorites using LaF−4 to suppress the 137Ba isobar during tandem accelerator mass spectrometry combined with a novel instrumental technique for isobar separation.