Low-Energy Accelerator Mass Spectrometry of actinides (236U, 237Np, 239, 240Pu) at the Centro Nacional de Aceleradores and its applications in oceanography
Notice bibliographique
Résumé
The development of high sensitivity Accelerator Mass Spectrometry (AMS) systems has allowed the study of a series of long-lived actinides at ultra-trace levels, opening new research topics. 236U (T1/2 = 2.34•107 y), 237Np (T1/2 = 2.14•106 y), 239Pu (T1/2 = 2.41•104 y) and 240Pu (T1/2 = 6.35•103 y) are present in the general environment mainly as a consequence of different uses of nuclear energy. Because of their specific inputs to the oceans and their long half-lives, they are very useful tools in oceanography to study different processes according to their characteristic behaviour in the marine environment. However, because of their extremely small concentrations in seawater, their analysis entails important challenges and the level of development and establishment of their corresponding techniques have been different. Although Pu isotopes have been commonly study in seawater, these studies have mainly focussed on the combined analysis of 239+240Pu by radiometric techniques. More recently, the study of 240Pu/239Pu isotopic ratios has been possible thanks to high sensitivity mass spectrometry techniques. During the last years, many efforts have been developed to study 236U in seawater because of its great potential as tracer of ocean currents but much work is still necessary to complete the currently scarce data set worldwide. In contrast, 237Np studies in seawater are almost non-existent mainly due to the challenges associated to its chemical isolation and the lack of a long-live Np isotope to be used as yield tracer and as normalization isotope for AMS analysis. In this context, this PhD thesis is targeted at the implementation of the 236U, 237Np and 239,240Pu AMS techniques for seawater studies at the CNA. In collaboration with the IAEA Environment Laboratories (IAEA-NAEL), in Monaco, a new method for the sequential extraction of 236U, 237Np and 239,240Pu has been successfully stablished based on the use of 242Pu to control not only the 239,240Pu radiochemical recovery but also the 237Np one. For the optimization of the AMS analysis of these radionuclides at the CNA, we have developed a comprehensive study of the use of He as stripper. The new figures of merit of the technique for 236U, 239Pu and 240Pu has been established and, furthermore, we have developed and implemented the 237Np AMS measurement technique at this facility by using 242Pu as normalization isotope (non-isotopic normalization). Finally, the new techniques developed in this thesis have been applied for the study of 236U, 237Np and 239,240Pu in different ocean environments (Namibian coast, in the south-eastern Atlantic Ocean, Canada Basin, in the Arctic Ocean and the north-western Mediterranean Sea), validating the corresponding procedures and contributing to increase the current database of these radionuclides in seawater.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».