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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Avaliação da biodisponibilidade dos radionuclídeos Ra-226, Ra-228 e Pb-210 presentes nos fertilizantes fosfatados e no fosfogesso de procedência nacional / Bioavailability of radionuclides 226Ra, 228Ra and 210Pb present in the brazilian phosphate fertilizers and phosphogypsum

Ana Carolina Russo 25 February 2013 (has links)
O fosfogesso, também denominado gesso agrícola, sub produto das industrias de fertilizantes fosfatados, pode ser utilizado como condicionador do solo devido a sua capacidade de proporcionar melhorias ao sistema solo-planta. No entanto, este resíduo concentra os radionuclídeos das séries do U e Th, presentes na rocha fosfatada usada como matéria prima, que podem impactar o meio ambiente. Com a finalidade de se verificar a concentração dos radionuclídeos biodisponíveis , foram analisadas amostras de fosfogesso e de fertilizantes fosfatados monoamônio fosfato e fertilizante superfosfato triplo, de duas procedências nacionais. A determinação da concentração de 226Ra, 228Ra e 210Pb se iniciou com a análise por espectrometria gama. Em seguida as amostras foram submetidas a um processo de extração branda com solução de EDTA-NH4 (0,05M) para que então o material lixiviado fosse analisado por meio de contagem alfa e beta total em detector proporcional de fluxo gasoso. Foram obtidos valores médios de extração de 1,6% - 1,7% para 210Pb, 0,5% - 1,4% para o 226Ra e 0,1% - 1,0% para o 228Ra nas amostras de fosfogesso. A baixa porcentagem de extração obtida para os radionuclídeos pode ser explicada tendo-se em vista que a solubilidade do fosfogesso variou de 7,7% a 16%. Para os fertilizantes fosfatados do tipo monoamônio fosfato os valores médios de extração foram inferiores a 26% para o 226Ra, inferiores a 10% para o 228Ra e inferiores a 10% para o 210Pb. Apesar da solubilidade da ordem de 77% dos fertilizantes fosfatados do tipo monoamônio fosfato, muito pouco dos radionuclídeos, presentes inicialmente, se concentraram na solução extraida. Para os fertilizantes fosfatados do tipo superfosfato triplo os valores médios de extração foram de 2,3% para o 226Ra, 1,2% para o 228Ra e 11,3% para o 210Pb. Mesmo com a solubilidade de 66% os fertilizantes fosfatados do tipo superfosfato triplo, muito pouco dos radionuclídeos, presentes inicialmente, se concentraram na solução extraida. / Phosphogypsum, also called gypsum, by-product of the phosphate fertilizer industry, can be used as soil conditioner since it provides improvements in the soil-plant system. However, this by-product concentrates radionuclides of the U and Th series, present in the phosphate rock used as raw material, which can impact the environment. In order to study the bioavailability of radionuclides, samples of phosphogypsum and phosphate fertilizers (monoammonium phosphate and triple superphosphate) were analyzed. The concentration of 226Ra, 228Ra and 210Pb were determined by gamma spectrometry. The samples were leached with a mild EDTA-NH4 (0,05M) solution and the radionuclides present in the final solution were determined by total alpha and beta counting on a gas flow proportional counter. The percentage of extraction varied from 1.6% to 1.7% for 210Pb, from 0.5% to 1.4% for 226Ra and from 0.1% to 1.0% for the 228Ra in phosphogypsum samples. The low percentage of extraction obtained for the radionuclides can be partly explained by the low solubility of phosphogypsum, which ranged from 7.7% to 16%. For the monoammonium phosphate samples the percentage of extraction were less than 26% for 226Ra, less than 10% for 228Ra and less than 10% for 210Pb. In spite of the high solubility of 77% of monoammonium phosphate in the EDTA-NH4 (0,05M) solution, low concentrations of radionuclides were observed in the extracted solution. For the triple superphosphate samples, the percentage of extraction was 2.3% for 226Ra, 1.2% for 228Ra and 11.3% for 210Pb. In spite of the high solubility of 66% of triple superphosphate in the EDTA-NH4 solution, low concentrations of radionuclides were observed in the extracted solution.
22

Characterization of Radioactivity in the Environment

Borrelli, Robert Angelo 10 November 1999 (has links)
"Ionizing radiation is produced as the result of the decay of an unstable nucleus. The standard measure of radioactivity is quantified according to the rate of disintegration of the unstable nucleus. This method of quantification does not incorporate the total amount of ionizing radiation that is associated with each disintegration of the radionuclide. The ionizing radiation that is produced as a result of decay is specific to a given radionuclide. A radionuclide can be conceptualized as a source of ionizing radiation. Disintegration of the unstable nucleus will therefore result in the continual release of ionizing radiation throughout the fixed existence of the radionuclide. This thesis will present a reasonable and practical adjustment to the current mechanism regarding the quantification of radionuclides. This adjustment will provide a basis to which the specific decay attributes of radionuclides can be normalized. Such a normalization will allow for direct comparisons among important inventories of radionuclides. This adjustment will be used to formulate a characterization of common radionuclides that exist in the environment. Such a characterization can provide a control inventory of ionizing radiation to which more specific systems of radionuclides can be compared."
23

Characterisation of stainless steel contamination in acidic media

Kerry, Timothy January 2018 (has links)
There is great interest in understanding the contamination of stainless steel by radionuclides across the nuclear fuel cycle. Through study of uptake mechanisms, contaminant localisation and process conditions that affect uptake, decontamination strategies can be tailored to remove built-up radioactive species. This study focusses on understanding stainless steel contamination by inactive lanthanides and radioactive actinide species (U, Np, Pu and Am) in acidic media. Through depth profiling, contamination has been seen to localise on the interface of the oxide layer and the bulk metal (at depths of up to 100 nm) indicating a potentially tenacious contamination mechanism. Furthermore, contaminant was observed at greater depths within the material (up to ~300 nm), suggesting penetration beyond the passive layer in to the bulk of the material. Long term immersion studies (up to 9 months) in 12 M HNO3 have also been undertaken to investigate the effect of surface corrosion on contaminant uptake. After 3 months the surface had undergone intergranular corrosion and grain droppage was observed. Further surface analysis revealed localisation of contaminants within the steel grain boundaries and vacancies. Once again, this may necessitate a more aggressive decontamination strategy. Conditions have been identified that enhance uptake of transuranic contaminants. Highest levels of uptake were seen in polished steel samples immersed in 4 M HNO3. The Np-237, Pu-239 and Am-241 contaminated samples showed surface concentrations of up to 1.2x107, 9.4x105 and 1x109 Bq/m2, respectively. In the case of Np contamination of stainless steel, microfocus X-ray absorption spectroscopy has shown the surface-mediated reduction of Np(V) leading to Np(IV) adsorption.
24

Utilização de líquens como bioindicadores de contaminação atmosférica por radionuclídeos naturais e metais em região impactada por TENORM / The use of lichens as bioindicators of atmospheric contamination by natural radionuclides and metals in a region impacted by TENORM

Lucio Leonardo 29 June 2010 (has links)
Este trabalho objetivou estudar a possibilidade de se utilizar líquen como bioindicador de poluição atmosférica para regiões impactadas por radionuclídeos, metais e elementos terras raras. Foram escolhidas como áreas de estudo a região de Pirapora do Bom Jesus, onde se localiza uma indústria de produção de estanho e chumbo metálicos e a região de Cubatão, onde se localiza o complexo industrial de produção de fertilizantes fosfatados. As duas instalações escolhidas são consideradas como indústrias TENORM - Technologically Enhanced Naturally Occurring Radioactive Material, pois podem ocasionar um aumento significativo na concentração dos radionuclídeos naturais nas várias etapas do processo industrial, ocasionando um aumento potencial de exposição à radiação natural em produtos, subprodutos e resíduos gerados. Para tanto foram analisados os radionuclídeos 238U, 226Ra, 210Pb, 232Th e 228Ra, os elementos terras raras e metais em amostras de matéria prima e resíduo das instalações, liquens e solos na área de influência. As amostras de líquen e solo foram analisadas para a determinação de urânio, tório, elementos terras raras e metais por análise por ativação com nêutrons. Os radionuclídeos 226Ra, 228Ra e 210Pb em amostras de solo foram determinados por espectrometria gama, e em amostras de liquens por separação radioquímica e contagem alfa e beta total em contador proporcional de fluxo de gás constante. As concentrações de 238U (de 19 a 473 Bq kg-1), 226Ra (de 21 a 265 Bq kg-1), 210Pb (de 401 a 1461 Bq kg-1), 232Th (de 15 a 574 Bq kg-1), 228Ra (de 176 a 535 Bq kg-1), elementos terras raras, Hf e Ta determinadas nas amostras de liquens ao redor da indústria de produção de estanho e chumbo metálicos mostram que todos estes elementos se concentram significativamente e, portanto, os liquens fornecem uma assinatura da contaminação atmosférica. Os resultados obtidos nas amostras de liquens da região de Cubatão mostram uma assinatura mais evidente do radionuclídeo 210Pb, proveniente de todo parque industrial da região. Os resultados obtidos no presente estudo mostraram que os liquens podem ser usados como bioindicadores de poluição atmosférica por radionuclídeos e elementos traço. / The main aim of this thesis is to study the possibility of using lichen as bioincicator of atmospheric pollution in regions contaminated by radionuclides, metals and rare earth elements. Two regions were chosen, one in Pirapora do Bom Jesus, where a tin and lead industry is located, and a second one in Cubatão, where a phosphate fertilizer industrial complex is located. The two industries chosen are considered as TENORM - Technologically Enhanced Naturally Occurring Radioactive Material, since they can cause a significant increase in the natural radionuclides concentration in the industrial process, and consequently a potential increase in the radiation exposure in products, byproducts and residue. To achieve this aim, the radionuclides 238U, 226Ra, 210Pb, 232Th and 228Ra, rare earth elements and metals were analyzed in samples of raw material an residue from the installations, lichens and soils. Lichens and soil samples were analyzed by instrumental neutron activation analysis for the determination of uranium, thorium, rare earth elements and metals. The radionuclides 226Ra, 228Ra and 210Pb in soil samples were determined by gamma spectrometry and in lichen sample by radiochemical separation and gross alpha and beta counting on a gas flow proportional counter. The concentrations of 238U (from 19 to 473 Bq kg-1), 226Ra (from 21 to 265 Bq kg-1), 210Pb (from 401 to 1461 Bq kg-1), 232Th (from 15 to 574 Bq kg-1), 228Ra (from 176 to 535 Bq kg-1), rare earth elements, Hf and Ta determined in lichen samples around the tin and lead industry show an enrichment in these elements. Therefore, the lichens can be used as a fingerprint of the atmospheric contamination. The results obtained for the lichen samples, in the Cubatão region, present a fingerprint mainly of 210Pb, from industries of the region. The results obtained in this study showed that the lichens can be used as bioindicators of atmospheric pollution by radionuclides and trace elements.
25

Avaliação da biodisponibilidade dos radionuclídeos Ra-226, Ra-228 e Pb-210 presentes nos fertilizantes fosfatados e no fosfogesso de procedência nacional / Bioavailability of radionuclides 226Ra, 228Ra and 210Pb present in the brazilian phosphate fertilizers and phosphogypsum

Russo, Ana Carolina 25 February 2013 (has links)
O fosfogesso, também denominado gesso agrícola, sub produto das industrias de fertilizantes fosfatados, pode ser utilizado como condicionador do solo devido a sua capacidade de proporcionar melhorias ao sistema solo-planta. No entanto, este resíduo concentra os radionuclídeos das séries do U e Th, presentes na rocha fosfatada usada como matéria prima, que podem impactar o meio ambiente. Com a finalidade de se verificar a concentração dos radionuclídeos biodisponíveis , foram analisadas amostras de fosfogesso e de fertilizantes fosfatados monoamônio fosfato e fertilizante superfosfato triplo, de duas procedências nacionais. A determinação da concentração de 226Ra, 228Ra e 210Pb se iniciou com a análise por espectrometria gama. Em seguida as amostras foram submetidas a um processo de extração branda com solução de EDTA-NH4 (0,05M) para que então o material lixiviado fosse analisado por meio de contagem alfa e beta total em detector proporcional de fluxo gasoso. Foram obtidos valores médios de extração de 1,6% - 1,7% para 210Pb, 0,5% - 1,4% para o 226Ra e 0,1% - 1,0% para o 228Ra nas amostras de fosfogesso. A baixa porcentagem de extração obtida para os radionuclídeos pode ser explicada tendo-se em vista que a solubilidade do fosfogesso variou de 7,7% a 16%. Para os fertilizantes fosfatados do tipo monoamônio fosfato os valores médios de extração foram inferiores a 26% para o 226Ra, inferiores a 10% para o 228Ra e inferiores a 10% para o 210Pb. Apesar da solubilidade da ordem de 77% dos fertilizantes fosfatados do tipo monoamônio fosfato, muito pouco dos radionuclídeos, presentes inicialmente, se concentraram na solução extraida. Para os fertilizantes fosfatados do tipo superfosfato triplo os valores médios de extração foram de 2,3% para o 226Ra, 1,2% para o 228Ra e 11,3% para o 210Pb. Mesmo com a solubilidade de 66% os fertilizantes fosfatados do tipo superfosfato triplo, muito pouco dos radionuclídeos, presentes inicialmente, se concentraram na solução extraida. / Phosphogypsum, also called gypsum, by-product of the phosphate fertilizer industry, can be used as soil conditioner since it provides improvements in the soil-plant system. However, this by-product concentrates radionuclides of the U and Th series, present in the phosphate rock used as raw material, which can impact the environment. In order to study the bioavailability of radionuclides, samples of phosphogypsum and phosphate fertilizers (monoammonium phosphate and triple superphosphate) were analyzed. The concentration of 226Ra, 228Ra and 210Pb were determined by gamma spectrometry. The samples were leached with a mild EDTA-NH4 (0,05M) solution and the radionuclides present in the final solution were determined by total alpha and beta counting on a gas flow proportional counter. The percentage of extraction varied from 1.6% to 1.7% for 210Pb, from 0.5% to 1.4% for 226Ra and from 0.1% to 1.0% for the 228Ra in phosphogypsum samples. The low percentage of extraction obtained for the radionuclides can be partly explained by the low solubility of phosphogypsum, which ranged from 7.7% to 16%. For the monoammonium phosphate samples the percentage of extraction were less than 26% for 226Ra, less than 10% for 228Ra and less than 10% for 210Pb. In spite of the high solubility of 77% of monoammonium phosphate in the EDTA-NH4 (0,05M) solution, low concentrations of radionuclides were observed in the extracted solution. For the triple superphosphate samples, the percentage of extraction was 2.3% for 226Ra, 1.2% for 228Ra and 11.3% for 210Pb. In spite of the high solubility of 66% of triple superphosphate in the EDTA-NH4 solution, low concentrations of radionuclides were observed in the extracted solution.
26

Entwicklung neuer radioaktiver Kupferkomplexe hoher Stabilität auf der Basis sechszähniger 3,7-Diazabicyclo[3.3.1]nonan-Derivate

Juran, Stefanie 07 January 2009 (has links) (PDF)
Die Entwicklung von Komplexbildnern für Kupferradionuklide im Hinblick auf eine nuklearmedizinische Anwendung ist ein intensiv bearbeitetes und in rascher Entwicklung begriffenes Forschungsgebiet. Dabei spielen verschiedene Faktoren – wie die günstigen kernphysikalischen Eigenschaften der verfügbaren Kupferradionuklide (Halbwertszeit, Umwandlungsart und -energien), die synthetische Zugänglichkeit und Modifizierbarkeit der Liganden sowie Markierungsausbeute und In-vivo-Stabilität der radioaktiven Kupferkomplexe – eine entscheidende Rolle. Liganden auf der Basis des 3,7-Diazabicyclo[3.3.1]nonans (Bispidine) besitzen für derartige radiopharmazeutische Anwendungen ein hohes Potential. Sie bilden mit Cu2+ sehr stabile Koordinationsverbindungen, wobei die Komplexstabilität im Bereich makrocyclischer Chelatoren liegt (logK ~ 20). Ferner weisen Bispidin-Derivate eine schnelle Komplexbildungskinetik mit Cu2+ auf. Damit sind radioaktiv markierte Bispidin-Liganden prinzipiell für einen Einsatz in der Nuklearmedizin (64Cu: Diagnostik, 67Cu: Therapie) geeignet und zwar insbesondere dann, wenn das Ligand-Grundgerüst mit zielsuchenden Biomolekülen, wie spezifischen Peptiden, Antikörpern oder Nukleinsäurebausteinen, funktionalisiert werden kann. Im Rahmen der vorliegenden Arbeit wurden neuartige sechszähnige Bispidin-Derivate mit Pyridyl-, Imidazolyl- und/oder Benzimidazolyl-Donoreinheiten mit Hilfe einer doppelten Mannich-Kondensation synthetisiert sowie koordinationschemisch und spektroskopisch charakterisiert. • Die Darstellung dieser Liganden erfolgte durch eine systematische Variation der Donoreinheiten an den C2/C4-Kohlenstoffatomen sowie den tertiären Aminostickstoffatomen N3/N7. Hierbei wurde insbesondere untersucht, wie sich der Einbau der unterschiedlichen Donorgruppen an den verschiedenen Positionen des Grundgerüsts auf das Löslichkeits- und Komplexbildungsverhalten auswirkt. Auf der Basis NMR-spektroskopischer Untersuchungen konnte gezeigt werden, dass die Einführung von Imidazolyl-Substituenten in N3- und N7 Position ausschließlich zu Isomeren führt, die eine trans-Stellung der Donoreinheiten an den C2/C4-Positionen aufweisen. Demgegenüber ist es möglich, durch den Einbau von Methylimidazolyl-Einheiten an C2 und C4, das im Hinblick auf die Komplexbildung mit Cu2+ gewünschte cis-Isomer zu isolieren. Diese Ergebnisse konnten anhand von Röntgenkristallstrukturanalysen der entsprechenden CuII-Komplexverbindungen bestätigt werden. • Mit Hilfe der Cyclovoltammetrie wurden CuII/CuI-Redoxpotentiale für ausgewählte CuII Bispidinkomplexe bestimmt. Da eine starke Korrelation dieser Redoxpotentiale mit den jeweiligen Stabilitätskonstanten besteht, können auf diese Weise Vorhersagen zur Komplexstabilität getroffen werden. Dabei konnte gezeigt werden, dass Bispidin-Liganden mit Pyridyl-Gruppen an N3/N7 sowie Methylimidazolyl- bzw. Pyridyl-Einheiten an C2/C4 sehr stabile Komplexe mit Cu2+ bilden. Hinsichtlich der synthetischen Zugänglichkeit ergeben sich jedoch für den Pyridyl-substituierten Liganden A Vorteile. Deshalb wurden Untersuchungen zur Biofunktionalisierung an diesem Derivat erprobt. Durch eine selektive Reduktion der Carbonylgruppe in 9-Stellung wurde der entsprechende Monoalkohol (B) als anti-Epimer dargestellt. Dieser Reaktionsschritt implizierte sowohl eine erhöhte chemische Stabilität des Liganden als auch eine gesteigerte Komplexstabilität des korrespondierenden CuII Komplexes. Die Hydrolyse der Methylestergruppen in Anwesenheit von Cäsiumhydroxid führte in hoher Ausbeute zur Verbindung C, welche an C1 und C5 über kupplungsfähige Carboxylgruppen verfügt. • Die Röntgenkristallstrukturen der CuII-Komplexe der Derivate B und C zeigen eine verzerrt oktaedrische Geometrie, wobei eine sechsfache Koordination mit dem Zentralatom vorzufinden ist. Dieser Aspekt führt zu einer nahezu vollständigen Abschirmung des Zentralatoms. Stabilitätsuntersuchungen auf der Basis der UV-Vis-Spektroskopie in Gegenwart des Konkurrenzliganden Glutathion ergaben, dass diese CuII-Komplexe selbst bei einem 100fachen Überschuss an Glutathion über mindestens 24 Stunden stabil sind. • Es wurde eine Reihe von Untersuchungen zur Kupplung von Linkereinheiten und Biomolekülen am Beispiel des Bispidin-Derivates C vollzogen. Im Rahmen der Arbeiten gelang es, Spacereinheiten wie γ-Aminobuttersäure, Ethylendiamin oder auch Maleinimid-Derivate an das Bispidin-Grundgerüst zu kuppeln. Die Funktionalisierung des Rückgrats mit Target-spezifischen Strukturen erfolgte anhand der Peptidsequenzen Neurotensin(8-13) und Bombesin(7-14). Dabei konnte demonstriert werden, dass eine Erhöhung der Ausbeuten an Peptidkonjugat ausgehend von Spacer-funktionalisierten Liganden erzielt werden kann. • Die radioaktive Markierung der Bispidin-Liganden mit den Radionukliden 64/67Cu verläuft unter physiologischen Bedingungen innerhalb weniger Minuten in hohen radiochemischen Ausbeuten (≥ 99%). In-vitro-Stabilitätsuntersuchungen (Rattenplasma, Challenge-Experimente mit Superoxid-Dismutase) an 64Cu-markierten Bispidin-Liganden und entsprechenden Peptidkonjugaten belegen, dass das Radionuklid über einen Zeitraum von 24 Stunden stabil gebunden bleibt. • Im Rahmen von In-vivo-Studien erfolgten Bioverteilungsuntersuchungen sowie Kleintier-PET-Aufnahmen an verschiedenen Bispidin-Derivaten. Das Bioverteilungsmuster der radiomarkierten Ligand- und Peptidkonjugat-Komplexe in männlichen Wistar-Ratten zeigte eine schnelle renale Ausscheidung der Verbindungen. Metabolitenanalysen bestätigten eine hohe In-vivo-Stabilität der 64Cu Bispidin-Komplexe. PET-Studien an PC3-Tumor-Mäusen unter Einsatz des 64Cu markierten Bispidin-Bombesin-Derivates belegen eine gute Tumoranreicherung dieser Verbindung sowie eine klare Visualisierung des Tumors.
27

Maisto radioaktyviosios taršos įtakos žmogaus vidinei apšvitai tyrimai, vertinimas ir prognozavimas / Investigation, assessment and prediction of internal exposure to public from the radioactive contamination of food

Ladygienė, Rima 08 December 2006 (has links)
Maisto radiologinio monitoringo, nustatant 90Sr ir 137Cs savituosius ir tūrinius aktyvumus, optimizavimo būdai nėra nagrinėti. Nenustatyta, kaip maisto mėginių radiologinių tyrimų rezultatai atspindi radionuklidų kiekį visame suvartotame maiste. Šiuo metu negalima atsakyti į klausimą, ar šalies gyventojų apšvita dėl 90Sr ir 137Cs maiste jonizuojančiosios spinduliuotės įvertinta pagal atliktų maisto radiologinių tyrimų rezultatus, buvo ir yra tikrai tokia, kokia buvo nustatyta ar nustatoma, t. y. trūksta duomenų apie tyrimų rezultatų reprezentatyvumą. Aplinkosauginiu ir ekonominiu poži��riu įvertinti maisto radiologinio monitoringo optimalumą bei parengti jo keitimo rekomendacijas dėl taršos aplinkoje lygių ir maisto produktų importo kaitos tendencijų yra aktualu, vengiant nepagrįstai didelių radiologinių tyrimų apimčių.Optimalus mėginių kiekis ir tinkamos mėginių rūšys įgalintų išvengti nepagrįstai didelės apšvitos gyventojams, tinkamai įvertinus vidutines dozes dėl 90Sr ir 137Cs maiste jonizuojančiosios spinduliuotės. Maisto radiologinio monitoringo optimizavimas svarbus ir dėl pastarųjų metų tendencijų atskirose valstybėse, taip pat ir Lietuvoje, planuojant plėtoti branduolinę energetiką. Įvertinus naujų technologijų su jonizuojančiosios spinduliuotės šaltiniais plėtrą atskirose socialinėse ekonominėse srityse, yra būtina optimali radiologinio monitoringo programa, garantuojanti gyventojų apsaugą nuo jonizuojančiosios spinduliuotės. / Aim of the disertation is optimization methods of food radiological monitoring. Evaluation using statistical programs was made for the results of radiological measurements of raw foodstuffs in Lithuania during 1965-2003. Calculations of annual effective dose caused by Sr-90 and Cs-137 in food for the public was made.
28

Development of Cyclotron Radionuclides for Medical Applications

Qaim, S. M. 19 May 2015 (has links) (PDF)
Soon after the discovery of radioactivity it was shown that radionuclides can be used both for diagnostic and therapeutic studies, depending on the characteristic radiations emitted by them. By 1960’s the radionuclide production technology using nuclear reactors was well established. In early 1970’s a renaissance of the cyclotrons occurred because many of the neutron deficient radionuclides could only be produced using irradiations with charged particles, like protons, deuterons, α-particles, etc. Initially, interest was directed towards radioactive gases for inhalation studies and other radionuclides for scintigraphy. Later, with the advent of emission tomography, i.e. Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET), the emphasis shifted to 123I and positron emitters [cf. 1–3], and tremendous progress ensued. In order to keep abreast of the fast developments, a Symposium was organized at the Brookhaven National Laboratory (BNL), USA, in 1976, with the title “Radiopharmaceutical Chemistry”. This became a biennial event, with alternate meetings in North America and Europe. It included all aspects of radionuclide and radiopharmaceutical research. About a decade later, however, it was realized that for discussion of technical aspects, a separate forum would be more appropriate. A group of experts therefore convened the first Targetry Workshop in Heidelberg in 1985. Thereafter it was established as a recurring Workshop, with its scope enlargened to include also nuclear and radiochemical problems. Today, the major conference on Radiopharmaceutical Sciences and the specialist International Workshop on Target-ry and Target Chemistry are held in alternate years. The present Workshop is No. 15 in the series and it is being jointly held by the research groups in Dresden and Prague, both of which have a long tradition of cyclotron production of radionuclides. In this talk, some personal reminiscences and impressions of the historical de-velopments in the field over the last 40 years will be briefly described.
29

Holocene Sedimentary Responses to Growth Faulting in a Back-Barrier Setting: East Matagorda Peninsula, Texas

Wolfe, Phillip 01 January 2014 (has links)
The structural framework of the northern Gulf of Mexico coastal zone is characterized by numerous growth fault systems. Neotectonic processes in coastal marshes in this region have been shown to be important drivers of relative sea-level rise as well as having significant influence on marsh accretion processes. One active growth fault has been identified at East Matagorda Peninsula, Texas. To characterize the Holocene behavior of this fault and the consequent sedimentary responses, a suite of fallout radionuclides (7Be, 137Cs, 210Pb) and radiocarbon, supplemented by sediment physical property data have been used to determine sediment mixing depths, rates of accumulation, and geochronology. Correlation of time-equivalent stratigraphic boundaries reveals a maximum total Holocene offset of ~1 meter. Determination of slip rates from these values reveals a linear trend of displacement as a function of distance along the fault trace with maximum slip occurring to the southwest and minimum slip to the northeast. Sediment accumulation rates from the downthrown station nearest to the fault trace display a dramatic increase over the last 30 years. Sediment bulk density and grain size data suggest an interaction between fault-driven geomorphic change and sedimentation where a migrating land-water interface has influenced the type of sediment accumulation here.
30

Assessing the anthropogenic impact on soil redistribution processes using radionuclides (10Be, 210Pb, 137Cs and 7Be) : a case study from the Christina River Basin, USA

Marquard, Julia January 2015 (has links)
Anthropogenic driven soil erosion has increased drastically within the last few centuries. Accelerated removal of topsoil degrades soil characteristics, decreasing the agricultural capacity to sustain food production for future human generations. In order to reduce sediment erosion to a minimum, soil movement dynamics have to be understood over relevant timescales. Emphasis is required on human land use, which has changed over time, altering erosion and deposition processes in the landscape. This thesis aims to understand the development of erosion with time and studies the effects of the anthropogenic impact on the Earth’s surface. A case study was conducted in the Christina River Basin in south-eastern Pennsylvania (USA) to evaluate the anthropogenic impact on sediment redistribution before and during European colonisation of the US East Coast. The Christina River Basin is focus of the Christina River Basin Critical Zone Observatory, where researchers of many disciplines (e.g. hydrology, geochemistry, geology, biology, geomorphology, soil science) study the interactions of the water, mineral and carbon cycle in relation to different land uses. This site is particularly suitable for this study due to the sudden change in land use with the arrival of European Settlers and the well-recorded history of land use in the area since. Besides sediment processes related to the European colonisation, special emphasis was placed on the last century and the particular impact of land management practices on the landscape. For the approach of this study, upland and depositional sediment profiles, as well as suspended sediment collected from rivers at different times were analysed for radionuclide activity. In particular, a combination of the short-lived radionuclides 7Be, 210Pb, and 137Cs with the long-lived meteoric nuclide 10Be was used to allow detection of sediment erosion as well as tracing of sediment source to streams over different time frames. Natural sediment processes were studied by investigating meteoric 10Be in different upland and valley hollow soil profiles in the Christina River Basin. Natu-ral sediment erosion rates of 17 to 18 mm per 1000 years and soil residence time of 26,000 to 57,000 years in upland sites classify the region to be characterised by slowly eroding soils. Valley hollow study sites indicate an alteration in sediment supply due to climate change within the last 80,000 years. Analysis of meteoric 10Be on suspended sediment in rivers with time (from pre-colonial to present times) and a comparison to the historical background of land use management indicated drastic changes in the sediment sources to the streams during the colonisation of the US East Coast. Such profound changes in the soil movement dynamics can be tied to a complete deforestation of the watershed during that time. However, a slow recovery of sediment sources to pre-colonial conditions within the last 100 years was observed, which may be related to the afforestation in parts of the watershed and change in farming practises. Examination of floodplains in recent history (last 100 years) using 210Pb and 137Cs identified a correlation between changes in land use and floodplain development. In particular, deforestation led to channel migration within the watershed, whereas afforestation reduced the flood magnitude. A discrimination of different sediment sources (agricultural and forest surface, channel migration) was detected on present suspended sediment by using a combination of tracers: 7Be, 137Cs, 210Pb and 10Be. About 50 % of sediment in the stream was attributed to channel migration classifying the stream as relatively unstable, whereas the second major sediment contribution was agricultural soil (32 %). As both sources are closely related to human activity in the study area, appropriate land management practices and stream channel stabilisation are of great importance for a hydro- and morphodynamic balance in future times. Results presented in this study provide evidence of the powerful impact anthropogenic land use has had on sediment movement in the Christina River Basin. More importantly, this study has shown the usefulness of combining long- and short-lived radionuclides to identify soil redistribution at different time periods and scales. Radionuclide data does not only reflect the drastic impact during European colonisation but also detects gradual changes that occur due to human action to limit soil erosion within the last century. This study indicates that some of the best management practices may minimise anthropogenic induced soil erosion, whilst simultaneously signifying the need to further improve land use management and reduce sediment erosion.

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