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Tiziano Tirabassi - One of the best experts on this subject based on the ideXlab platform.

  • analytical formulation for the Radioactive Contaminant released from nuclear power plants
    Artificial Intelligence Review, 2012
    Co-Authors: B E J Bodmann, Umberto Rizza, Daniela Buske, M T Vilhena, Tiziano Tirabassi
    Abstract:

    In this contribution we discuss analytical modelling of Radioactive substance dispersionthatresultsfromeithercontrolledoraccidentalreleaseby nuclearpower plants. Our model is based on the three-dimensional advection–diffusion equation with mean wind velocity field from observation. All meteorological parameters are determined using the meso-scale Weather Research and Forecasting (WRF) platform. The obtained solution permits us to simulate Radioactive substances dispersion in a turbulent regime in the environment around a power plant, which is of interest for nuclear reactor accident scenarios and their related emergency actions. We discuss the closed form method for solving the equation which is then applied to Radioactive substance dispersion. Finally, the results of the model are presented.

Mancuso Michele - One of the best experts on this subject based on the ideXlab platform.

  • Developpement et optimisation de détecteurs de lumière innovants et bolométres scintillants pour une expérience pilote sur la double désintégration bêta sans émission de neutrinos
    Italy, 2016
    Co-Authors: Mancuso Michele
    Abstract:

    The PhD work described in this manuscript was performed in the framework of the LUMINEU project, a pilot search for the neutrinoless double beta decay (0νββ) of the isotope in 100Mo with ZnMoO4 scintillating bolometers. The main PhD activity has consisted the development of a particle detection technology able to fulfill the requirement of a next generation experiment on 0νββ capable of exploring the inverted hierarchy region of the neutrino mass pattern. We report about an experimental physics work involving progress in detector prototype design and tests, and development of tools in view of a large experiment preparation. The neutrinoless double beta decay is a hypothetical rare nuclear transition with a half life T1/2>1025 years, which is possible for some nuclei with an even number both of protons and neutrons. In the 0νββ transition two neutrons decay simultaneously in two protons with the emission of only two electrons. In a first approximation it can be seen as two simultaneous β-decays where the two neutrinos act as a single virtual particle joining the two decay vertices. It is demonstrated that any process which leads to 0νββ is possible only if ν≡ ν̄ˉ, i.e. the neutrino is a Majorana particle, which is in contrast with the Standard Model assumptions. Therefore, the observation of this phenomenon can determine the Majorana nature of massive neutrinos. This is of fundamental importance to make progress in our understanding of the origin of neutrino masses and mixing and of the symmetries governing the lepton sector of particle interactions. The measurement of the T1/2 of the process would give unvaluable information on the absolute scale of neutrino masses, the type of neutrino mass spectrum and the Majorana phases. The detection approach adopted in this thesis is the homogeneous bolometric technique, which fits well the detector characteristics needed to investigate rare events. The detector provides high efficiency and a very good energy resolution and, thanks to a scintillating absorber, it allows particle discrimination for background suppression. As can be easily understood, the control of the background is crucial to measure such rare decays. The first part of this thesis focuses on the neutrino physics and on the 0νββ decay; moreover the experimental detection approaches are briey discussed and the sensitivity to the half life of a 0νββ experiment is discussed. To understand the progress achieved in the technology development, the following chapter is dedicated to the detector physics: the components of a bolometer, a simple thermal model, and the detector response are introduced. The second part of this work is dedicated to the setup. The detectors used work at very low temperatures (~10 mK), thus sophisticated thermal machines are needed; the working principles of these cryogenic systems are presented focusing on the details of the ones used in this work. Since the experimental work discussed in this thesis concerns the detector assembly and measurement, the data acquisition and analysis are discussed in details too. The final part of the thesis is devoted to the results, starting with the progress made on bolometric light detectors: a description and optimization of the light detector design, the effect of anti-reflective coating and the thermal response enhancement obtained with the Neganov-Luke effect are presented. The results on the development of the LUMINEU prototype detectors and the measurements are summarized, from the working tests to the Radioactive Contaminant measurements. The growth and purification process of the ZnMoO4 crystals are also presented. Based on these results, a final sensitivity of a future experiment based on this detector is computed. Finally we present a spin-off of the LUMINEU project consisting in a scintillating bolometer prototype made with an alternative compound absorber, Li2MoO4. We examine the advantages and disadvantages with respect to the ZnMoO4. This manuscript aims at being a guide to an experimental approach for the search for neutrinoless double beta decay, a manual for scintillating bolometer operations and a report about the successful LUMINEU project. Le travail de doctorat exposé dans ce manuscrit a été développé dans le cadre du projet LUMINEU, une expérience pilote pour la double désintégration bêta sans émission de neutrinos (0νββ) de l'isotope 100Mo avec des bolométres scintillants de ZnMoO4. L'activité principale du doctorat consistait en le développement d'une technologie de détection de particules capable de satisfaire les conditions nécessaire d'une experience de 0νββ de nouvelle génération qui soit capable d'examiner la région de la hiérarchie inversée du modèle de la masse du neutrino. Nous exposons un travail de physique expérimentale qui implique l'avancement du design et des tests des prototypes de détecteurs, et le développement des outils en vue de la préparation d'une expérience importante. La double désintégration bêta sans émission de neutrinos est une hypothétique transition nucléaire rare avec une demi-vie de T1/2>1025 ans, qui est possible pour certains noyaux avec un nombre pair de protons et de neutrons. Dans la transition 0νββ deux neutrons se désintégrent simultanément en deux protons avec l'émission de deux électrons seulement. Dans une première approximation, ce peut être vu comme deux β désintégrations où les deux neutrinos agissent comme une seule particule virtuelle en joignant les deux sommets de désintégration. Il est prouvé que n'importe quel processus qui conduit au 0νββ est possible seulement si if ν≡ ν̄ˉ, v.g. le neutrino est une particule de Majorana, qui contraste avec les hypothéses du Modèle Standard. Par conséquence, l'observation de ce phénomène peut déterminer la nature Majorana des neutrinos massifs. C'est très important de faire progresser notre compréhension de l'origine de la masse et de la composition des neutrinos et de la symétrie qui régit le secteur des leptons des interactions de particules. La mesure du T1/2 du processus peut fournir des informations inestimables sur l'échelle absolue de la masse des neutrinos, sur le type de spectre de masse des neutrinos et sur les phases de Majorana. La méthode de détection adoptée dans cette thèse est la technique bolométrique, qui s'intègre bien avec les caractéristiques requises des détecteurs pour étudier les événements rares. Le détecteur fournit une grande efficacité et une très bonne résolution en énergie et, grâce à un absorbeur scintillant, il permet la discrimination des particules pour la suppression du fond. Comme on peut bien comprendre, le contrôle du background est crucial pour mesurer ces désintégrations rares. La première partie de cette thèse se concentre sur la physique du neutrino et sur la désintégration 0νββ; en outre, les méthodes de détection expérimentales et la sensibilité de la demi-vie d'une expérience 0νββ sont traitées. Pour comprendre les progrès réalisés dans le développement de la technologie, le chapitre suivant est dédié à la physique des détecteurs: les composants d'un bolomètre, un modèle thermique simple, et la réponse d'un détecteur sont présentés. La deuxième partie de ce travail est dédiée au setup. Les détecteurs utilisés fonctionnent aux très basses températures (~10 mK), par conséquent, des machines thermique sophistiquées sont nécessaires; les principes de fonctionnement de ces systèmes cryogéniques sont présentés en se concentrant sur les détails de ceux qui ont été utilisés dans ce travail. Puisque l'activité expérimentale présentée dans cette thèse porte sur l'assemblage et sur les mesures du détecteur, aussi l'acquisition et l'analyse des données sont traités en détails. La dernière partie de la thèse est consacrée aux résultats, à commencer par les progress réalisés dans le détecteurs bolométriques de lumière: une description et optimisation du design des détecteurs de lumiére, l'effet du traitement antireet et l'amélioration de la réponse thermique obtenue avec l'effet Neganov-Luke sont présentés. Les résultats sur le développement des prototypes des détecteurs LUMINEU et les mesures sont résumés. Les processus de croissance et purification des cristaux ZnMoO4 sont aussi présentés. Sur la base de ces résultats nous avons calculé une sensibilité finale sur une expérience à venir basée sur ces détecteurs. Enfin, nous présentons un spin-off du projet LUMINEU qui consiste dans un prototype d'un bolomètre scintillant réalisé avec un absorbeur composé alternatif, Li2MoO4. Nous examinons les avantages et les désavantages par rapport au ZnMoO4. Ce manuscrit a comme but d'être un guide à une approche expérimentale pour la recherche de la double désintégration bêta sans émission de neutrinos, un manuel pour les opérations de bolomètres scintillants et un rapport sur l'expérience réussie du projet LUMINEU

  • Developpement et optimisation de d\ue9tecteurs de lumi\ue8re innovants et bolom\ue9tres scintillants pour une exp\ue9rience pilote sur la double d\ue9sint\ue9gration b\ueata sans \ue9mission de neutrinos
    country:Italy, 2016
    Co-Authors: Mancuso Michele
    Abstract:

    The PhD work described in this manuscript was performed in the framework of the LUMINEU project, a pilot search for the neutrinoless double beta decay (0\u3bd\u3b2\u3b2) of the isotope in 100Mo with ZnMoO4 scintillating bolometers. The main PhD activity has consisted the development of a particle detection technology able to fulfill the requirement of a next generation experiment on 0\u3bd\u3b2\u3b2 capable of exploring the inverted hierarchy region of the neutrino mass pattern. We report about an experimental physics work involving progress in detector prototype design and tests, and development of tools in view of a large experiment preparation. The neutrinoless double beta decay is a hypothetical rare nuclear transition with a half life T1/2>1025 years, which is possible for some nuclei with an even number both of protons and neutrons. In the 0\u3bd\u3b2\u3b2 transition two neutrons decay simultaneously in two protons with the emission of only two electrons. In a first approximation it can be seen as two simultaneous \u3b2-decays where the two neutrinos act as a single virtual particle joining the two decay vertices. It is demonstrated that any process which leads to 0\u3bd\u3b2\u3b2 is possible only if \u3bd 61 \u3bd\u304\u2c9, i.e. the neutrino is a Majorana particle, which is in contrast with the Standard Model assumptions. Therefore, the observation of this phenomenon can determine the Majorana nature of massive neutrinos. This is of fundamental importance to make progress in our understanding of the origin of neutrino masses and mixing and of the symmetries governing the lepton sector of particle interactions. The measurement of the T1/2 of the process would give unvaluable information on the absolute scale of neutrino masses, the type of neutrino mass spectrum and the Majorana phases. The detection approach adopted in this thesis is the homogeneous bolometric technique, which fits well the detector characteristics needed to investigate rare events. The detector provides high efficiency and a very good energy resolution and, thanks to a scintillating absorber, it allows particle discrimination for background suppression. As can be easily understood, the control of the background is crucial to measure such rare decays. The first part of this thesis focuses on the neutrino physics and on the 0\u3bd\u3b2\u3b2 decay; moreover the experimental detection approaches are briey discussed and the sensitivity to the half life of a 0\u3bd\u3b2\u3b2 experiment is discussed. To understand the progress achieved in the technology development, the following chapter is dedicated to the detector physics: the components of a bolometer, a simple thermal model, and the detector response are introduced. The second part of this work is dedicated to the setup. The detectors used work at very low temperatures (~10 mK), thus sophisticated thermal machines are needed; the working principles of these cryogenic systems are presented focusing on the details of the ones used in this work. Since the experimental work discussed in this thesis concerns the detector assembly and measurement, the data acquisition and analysis are discussed in details too. The final part of the thesis is devoted to the results, starting with the progress made on bolometric light detectors: a description and optimization of the light detector design, the effect of anti-reflective coating and the thermal response enhancement obtained with the Neganov-Luke effect are presented. The results on the development of the LUMINEU prototype detectors and the measurements are summarized, from the working tests to the Radioactive Contaminant measurements. The growth and purification process of the ZnMoO4 crystals are also presented. Based on these results, a final sensitivity of a future experiment based on this detector is computed. Finally we present a spin-off of the LUMINEU project consisting in a scintillating bolometer prototype made with an alternative compound absorber, Li2MoO4. We examine the advantages and disadvantages with respect to the ZnMoO4. This manuscript aims at being a guide to an experimental approach for the search for neutrinoless double beta decay, a manual for scintillating bolometer operations and a report about the successful LUMINEU project. Le travail de doctorat expos\ue9 dans ce manuscrit a \ue9t\ue9 d\ue9velopp\ue9 dans le cadre du projet LUMINEU, une exp\ue9rience pilote pour la double d\ue9sint\ue9gration b\ueata sans \ue9mission de neutrinos (0\u3bd\u3b2\u3b2) de l'isotope 100Mo avec des bolom\ue9tres scintillants de ZnMoO4. L'activit\ue9 principale du doctorat consistait en le d\ue9veloppement d'une technologie de d\ue9tection de particules capable de satisfaire les conditions n\ue9cessaire d'une experience de 0\u3bd\u3b2\u3b2 de nouvelle g\ue9n\ue9ration qui soit capable d'examiner la r\ue9gion de la hi\ue9rarchie invers\ue9e du mod\ue8le de la masse du neutrino. Nous exposons un travail de physique exp\ue9rimentale qui implique l'avancement du design et des tests des prototypes de d\ue9tecteurs, et le d\ue9veloppement des outils en vue de la pr\ue9paration d'une exp\ue9rience importante. La double d\ue9sint\ue9gration b\ueata sans \ue9mission de neutrinos est une hypoth\ue9tique transition nucl\ue9aire rare avec une demi-vie de T1/2>1025 ans, qui est possible pour certains noyaux avec un nombre pair de protons et de neutrons. Dans la transition 0\u3bd\u3b2\u3b2 deux neutrons se d\ue9sint\ue9grent simultan\ue9ment en deux protons avec l'\ue9mission de deux \ue9lectrons seulement. Dans une premi\ue8re approximation, ce peut \ueatre vu comme deux \u3b2 d\ue9sint\ue9grations o\uf9 les deux neutrinos agissent comme une seule particule virtuelle en joignant les deux sommets de d\ue9sint\ue9gration. Il est prouv\ue9 que n'importe quel processus qui conduit au 0\u3bd\u3b2\u3b2 est possible seulement si if \u3bd 61 \u3bd\u304\u2c9, v.g. le neutrino est une particule de Majorana, qui contraste avec les hypoth\ue9ses du Mod\ue8le Standard. Par cons\ue9quence, l'observation de ce ph\ue9nom\ue8ne peut d\ue9terminer la nature Majorana des neutrinos massifs. C'est tr\ue8s important de faire progresser notre compr\ue9hension de l'origine de la masse et de la composition des neutrinos et de la sym\ue9trie qui r\ue9git le secteur des leptons des interactions de particules. La mesure du T1/2 du processus peut fournir des informations inestimables sur l'\ue9chelle absolue de la masse des neutrinos, sur le type de spectre de masse des neutrinos et sur les phases de Majorana. La m\ue9thode de d\ue9tection adopt\ue9e dans cette th\ue8se est la technique bolom\ue9trique, qui s'int\ue8gre bien avec les caract\ue9ristiques requises des d\ue9tecteurs pour \ue9tudier les \ue9v\ue9nements rares. Le d\ue9tecteur fournit une grande efficacit\ue9 et une tr\ue8s bonne r\ue9solution en \ue9nergie et, gr\ue2ce \ue0 un absorbeur scintillant, il permet la discrimination des particules pour la suppression du fond. Comme on peut bien comprendre, le contr\uf4le du background est crucial pour mesurer ces d\ue9sint\ue9grations rares. La premi\ue8re partie de cette th\ue8se se concentre sur la physique du neutrino et sur la d\ue9sint\ue9gration 0\u3bd\u3b2\u3b2; en outre, les m\ue9thodes de d\ue9tection exp\ue9rimentales et la sensibilit\ue9 de la demi-vie d'une exp\ue9rience 0\u3bd\u3b2\u3b2 sont trait\ue9es. Pour comprendre les progr\ue8s r\ue9alis\ue9s dans le d\ue9veloppement de la technologie, le chapitre suivant est d\ue9di\ue9 \ue0 la physique des d\ue9tecteurs: les composants d'un bolom\ue8tre, un mod\ue8le thermique simple, et la r\ue9ponse d'un d\ue9tecteur sont pr\ue9sent\ue9s. La deuxi\ue8me partie de ce travail est d\ue9di\ue9e au setup. Les d\ue9tecteurs utilis\ue9s fonctionnent aux tr\ue8s basses temp\ue9ratures (~10 mK), par cons\ue9quent, des machines thermique sophistiqu\ue9es sont n\ue9cessaires; les principes de fonctionnement de ces syst\ue8mes cryog\ue9niques sont pr\ue9sent\ue9s en se concentrant sur les d\ue9tails de ceux qui ont \ue9t\ue9 utilis\ue9s dans ce travail. Puisque l'activit\ue9 exp\ue9rimentale pr\ue9sent\ue9e dans cette th\ue8se porte sur l'assemblage et sur les mesures du d\ue9tecteur, aussi l'acquisition et l'analyse des donn\ue9es sont trait\ue9s en d\ue9tails. La derni\ue8re partie de la th\ue8se est consacr\ue9e aux r\ue9sultats, \ue0 commencer par les progress r\ue9alis\ue9s dans le d\ue9tecteurs bolom\ue9triques de lumi\ue8re: une description et optimisation du design des d\ue9tecteurs de lumi\ue9re, l'effet du traitement antireet et l'am\ue9lioration de la r\ue9ponse thermique obtenue avec l'effet Neganov-Luke sont pr\ue9sent\ue9s. Les r\ue9sultats sur le d\ue9veloppement des prototypes des d\ue9tecteurs LUMINEU et les mesures sont r\ue9sum\ue9s. Les processus de croissance et purification des cristaux ZnMoO4 sont aussi pr\ue9sent\ue9s. Sur la base de ces r\ue9sultats nous avons calcul\ue9 une sensibilit\ue9 finale sur une exp\ue9rience \ue0 venir bas\ue9e sur ces d\ue9tecteurs. Enfin, nous pr\ue9sentons un spin-off du projet LUMINEU qui consiste dans un prototype d'un bolom\ue8tre scintillant r\ue9alis\ue9 avec un absorbeur compos\ue9 alternatif, Li2MoO4. Nous examinons les avantages et les d\ue9savantages par rapport au ZnMoO4. Ce manuscrit a comme but d'\ueatre un guide \ue0 une approche exp\ue9rimentale pour la recherche de la double d\ue9sint\ue9gration b\ueata sans \ue9mission de neutrinos, un manuel pour les op\ue9rations de bolom\ue8tres scintillants et un rapport sur l'exp\ue9rience r\ue9ussie du projet LUMINEU

Sophie Ayrault - One of the best experts on this subject based on the ideXlab platform.

  • depth distribution of cesium 137 in paddy fields across the fukushima pollution plume in 2013
    Journal of Environmental Radioactivity, 2015
    Co-Authors: Hugo Lepage, Olivier Evrard, Yuichi Onda, Irene Lefevre, Patrick J Laceby, Sophie Ayrault
    Abstract:

    Abstract Large quantities of radiocesium were deposited across a 3000 km2 area northwest of the Fukushima Dai-ichi nuclear power plant after the March 2011 accident. Although many studies have investigated the fate of 137Cs in soil in the months following the accident, the depth distribution of this Radioactive Contaminant in rice paddy fields requires further examination after the typhoons that occurred in this region. Such investigations will help minimize potential human exposure in rice paddy fields. Radionuclide activity concentrations, organic content and particle size were analysed in 10 soil cores sampled from paddy fields in November 2013, 20 km north of the Fukushima power plant. Our results demonstrate limited depth migration of 137Cs with the majority concentrated in the uppermost layers of soils (

  • Tracking the origin and dispersion of contaminated sediments transported by rivers draining the Fukushima Radioactive Contaminant plume
    Proceedings of the International Association of Hydrological Sciences, 2015
    Co-Authors: Hugo Lepage, Yuichi Onda, Irene Lefevre, Sophie Ayrault, O. Evrard, Caroline Chartin, Philippe Bonté
    Abstract:

    This study was conducted in several catchments draining the main Fukushima Dai-ichi Power Plant Contaminant plume in Fukushima prefecture, Japan. We collected soils and sediment drape deposits (n = 128) and investigated the variation in $^{137}$Cs enrichment during five sampling campaigns, conducted every six months, which typically occurred after intense erosive events such as typhoons and snowmelt. We show that upstream contaminated soils are eroded during summer typhoons (June-October) before being exported during the spring snowmelt (March-April). However, this seasonal cycle of sediment dispersion is further complicated by the occurrence of dam releases that may discharge large amounts of Contaminants to the coastal plains during the coming years.

B E J Bodmann - One of the best experts on this subject based on the ideXlab platform.

  • on an analytical model for the Radioactive Contaminant release in the atmosphere from nuclear power plants
    2012
    Co-Authors: M T Vilhena, B E J Bodmann, Umberto Rizza, Daniela Buske
    Abstract:

    While the renaissance of nuclear power was motivated by the increasing energy demand and the related climate problem, the recent history of nuclear power, more specifically two disastrous accidents have forced focus on nuclear safety. Although, experience gathered along nuclear reactor developments has sharpened the rules and regulations that lead to the commissioning of latest generation nuclear technology, an issue of crucial concern is the environmental monitoring around nuclear power plants. These measures consider principally the dispersion of Radioactive material that either may be released in control actions or in accidents, where in the latter knowledge from simulations guide the planning of emergency actions. In this line the following contribution focuses on the question of Radioactive material dispersion after discharge from a nuclear power plant.

  • analytical formulation for the Radioactive Contaminant released from nuclear power plants
    Artificial Intelligence Review, 2012
    Co-Authors: B E J Bodmann, Umberto Rizza, Daniela Buske, M T Vilhena, Tiziano Tirabassi
    Abstract:

    In this contribution we discuss analytical modelling of Radioactive substance dispersionthatresultsfromeithercontrolledoraccidentalreleaseby nuclearpower plants. Our model is based on the three-dimensional advection–diffusion equation with mean wind velocity field from observation. All meteorological parameters are determined using the meso-scale Weather Research and Forecasting (WRF) platform. The obtained solution permits us to simulate Radioactive substances dispersion in a turbulent regime in the environment around a power plant, which is of interest for nuclear reactor accident scenarios and their related emergency actions. We discuss the closed form method for solving the equation which is then applied to Radioactive substance dispersion. Finally, the results of the model are presented.

Uchida Shigeo - One of the best experts on this subject based on the ideXlab platform.

  • Insolubilization of technetium by bacteria living in ponding water in paddy fields
    2019
    Co-Authors: Ishii Nobuyoshi, Tagami Keiko, Uchida Shigeo
    Abstract:

    Technetium-99 is a Radioactive Contaminant in the environment, which results from fallout from nuclear weapons testing, nuclear fuel reprocessing, and the disposal of low- and intermediate-level wastes. The half-life of Tc-99 is 210,000 years, implying that this radionuclide will persist in the environment for many years. For these reasons, prediction of the behavior of Tc-99 is desirable. Because the behavior of elements depends on their chemical forms, the authors investigated the physicochemical forms of Tc in ponding water in Japanese paddy fields. When a Radioactive tracer 95mTcO4- was added to the ponding water, more than 70% of the tracer transformed from soluble TcO4- to insoluble form, which is > 0.2-um in size. The amount of insoluble Tc was decreased by the addition of antibiotics on bacteria to the ponding water sample. The decrease of insoluble Tc amount, however, was not observed by the addition of an antibiotic on fungi. Therefore, the insoluble Tc was caused by bacteria living in ponding water. In addition to these results, the authors will also discuss the behavior of Tc in paddy fields.SETAC Europe 14th Annual Meetin

  • Environmental conditions for insoluble Tc formation in ponding water above a paddy field
    2019
    Co-Authors: Ishii Nobuyoshi, Koiso Hiroyuki, Takeda Hiroshi, Uchida Shigeo
    Abstract:

    Technetium-99 is a Radioactive Contaminant in marine and terrestrial environments. Under oxic conditions, it is present as the pertechnetate anion [Tc(VII)O4-], which is soluble and mobile in the environment. In paddy fields in Japan, the accumulation of Tc in the 20-cm plow layer was observed (Tagami and Uchida 2002). Since paddy fields are flooded during the planting season, reductive conditions develop in the plowed layer. Under reductive conditions, Tc is transformed from Tc(VII) O4- to Tc(IV) species. Tc(IV) species generally are insoluble and immobile in the environment, and thus Tc(IV) could accumulate in the plowed layer.Recently, it was found that gram-negative-bacteria were responsible for the formation of insoluble Tc in the ponding water of flooded paddy fields (Ishii and Uchida 2005). This insolubilization would be one of the factors of the Tc accumulation in the plowed layer because bacteria sink into the plowed layers due to their own weight over time. However, little information is available for environmental conditions of Tc insolubilizing by the bacteria. In this study, optimum oxic conditions for the insolubilization were determined.18th World Congress of Soil Scienc

  • Transformation of insoluble technetium to soluble forms by bacterivorous ciliate
    2019
    Co-Authors: Ishii Nobuyoshi, Uchida Shigeo
    Abstract:

    Technetium-99 (99Tc) is a long-lived (half-life, 2.1 x 105 y) Radioactive Contaminant in the environment. Under aerobic conditions, Tc is present in the heptavalent form as pertechnetate ion (TcO4-). This chemical species is soluble and mobile in the environment and is readily taken up by plants. Therefore, we would like to be able to predict the behavior of 99Tc in the environment. Recently, we found transformation of Tc from soluble to insoluble forms in ponding water of paddy fields [1] and bacterial involvement in this transformation [2]. One of the Tc insolubilizing mechanisms would be an accumulation of Tc by bacteria as demonstrated by Lloyd et al. [3]. In aquatic environments, bacteria are ingested by heterotrophic nanoflagellates and ciliates as their food, and thus the bacterial ingestion by these protozoa would govern the fate of Tc. Our aim, therefore, was to determine the fate of the insoluble Tc accumulating by bacterial cells after the bacterial ingestion by protozoa: Whether the insoluble Tc is concentrated and kept inside of the protozoan cells or it is excreted outside of the protozoan.\nA ciliate Tetrahymena thermophila and a bacterium Escherichia coli AB1157 were used as a prey-predator model. E. coli was incubated with 99TcO4- for 45 days to accumulate Tc within the cell. After the incubation, cells were washed 5 times and then cultured with and without T. thermophila. To estimate soluble Tc excretion by T. thermophila, the cultures were filtered through a 0.2 ?m pore-size filter, and radioactivity of 99Tc in the filtrate was measured with a liquid scintillation counter. The values of measurements were converted to concentrations (Bq mL-1).\nThe concentration of the soluble Tc in the filtrate of the E. coli-alone culture gradually increased from 28.7 Bq mL-1 at the beginning of incubation (day 0) to the maximum concentration 168.3 Bq mL-1 at the end of incubation (day 7). An increase in the soluble Tc concentration was also observed in the filtrate of the E. coli and T. thermophila mixed culture, with the maximum concentration, 352.1 Bq mL-1 at day 3. The maximum concentration of the soluble Tc was 2.1-times higher in the mixed culture than in the E. coli alone culture.The abundance of T. thermophila cells in the mixed culture increased from 1.3 x 103 to 4.7 x 103 cells mL-1 for the first 3 days of incubation. The growth period of T. thermophila cells corresponded to the period of the significant increase in the concentration of the soluble Tc in the mixed culture. If T. thermoplila concentrated and kept Tc inside of cells, the concentration of soluble Tc would have decrease during the growth period. Therefore, the increase in soluble Tc suggested that the insoluble Tc was transformed to soluble forms in the food vacuoles of the T. thermophila cells and then was excreted out from the cells.\nReferences[1] N. Ishii, K. Tagami, and S. Uchida, Chemosphere. 57. 953 (2004).[2] N. Ishii, and K. Tagami, Radioisotopes. 52. 475 (2003).[3] J. R. Lloyd, J. A. Cole, and L. E. Macaskie, J Bacteriol. 179, 2014 (1997).The 2nd International Conference on Radioactivity in the Environmen

  • Influence of microbial community on the behaviors of technetium and other trace elements in water covering rice paddy soils
    2019
    Co-Authors: Ishii Nobuyoshi, Tagami Keiko, Enomoto Shuichi, Uchida Shigeo
    Abstract:

    The release of radionuclides into the environment is a subject of public concern. Technetium-99 (99Tc) is a Radioactive Contaminant in the environment and has been accumulating because of its long half-life of 2.1 x 10E+5 y. This radionuclide is highly soluble and available for plants under aerobic conditions as TcO4-, but the reduced form of Tc, Tc(IV), is insoluble and biological inactive. Some anaerobic microorganisms have been shown to reduce TcO4- to insoluble Tc(IV) through their anaerobic energy metabolism. Generally, such bacteria are found in soils under waterlogged conditions, i.e. paddy fields. Chemical behavior of Tc in water covering paddy field soils, however, is not well known. In this study, we pay attention on the insolubilization of Tc by the activity of microbial community in the water body of waterlogged soils. Furthermore insolubilizations of other trace elements were also studied because the microbial community insolubilized Tc could affect on the fate of other trace elements as well.First, microbial communities in soils were checked their abilities of Tc insolubilization from TcO4-. Nine paddy field soil samples were flooded with 0.3% glucose water and incubated for 7 days. After the incubation, the water covering the soil sample was transferred into a new test tube, and 95mTcO4- was added to the tube as a radiotracer. At 4 days after the addition of 95mTc, the solution was separated into four fractions, that is, insoluble-Tc, pertechnetate, cationic-Tc, and Tc in other forms, by passing the solution through a 0.2 micro m-pore-size membrane filter, a TEVA resin column, and a cation exchange resin column.The results showed that the dominant Tc chemical form in most of the samples was TcO4-. However, on average, 16.9% of the added 95mTcO4- changed to insoluble forms and the maximum Tc insolubilization, 76.2 +/- 9.2%, was found in a soil (P38). When the P38 sample was subjected to further studies, it was observed that the insolubilization percentage was decreased to 3.6 +/- 0.5% by removing microorganisms from the water body, and the percentage was also decreased to 23.4 +/- 0.8% by adding antibiotics to depress metabolism of bacteria. These results suggested that TcO4- could be insolubilized in the water covering soils by living bacteria.Then, the behaviors of trace elements in water covering P38 were also studied using the same method. To trace elements, a multitracer solution produced in RIKEN Ring Cyclotron was added to the tubes. The multitracer solution included the following short-lived radionuclides: 7Be, 46Sc, 75Se, 83Rb, 85Sr, 88Y, 95Nb. 95mTc, 139Ce, 143Pm, 153Gd, 169Yb, 175Hf, and 183Re. After 4 days of the incubation with the multitracers, the culture was sequentially separated into 4 fractions as described in above. The radioactivities in the fractions were analyzed using a Ge detecting systems (Seiko EG &G).For the elements except Rb, Sr, and Re, more than 80% of the elements were trapped by the membrane filter, while >70% of Rb and Sr were retained in the cation resin column. Rhenium is a congener of Tc in the group VIIa, but 28.2 +/- 1.9% of Re was trapped by the membrane filter. Most of Re was trapped on the TEVA resin. The high retention ratios of trace elements by the membrane filtration indicated that the Tc insolubilizing microbial community would be applied for biological treatment of 99Tc and other trace elements/radionuclides by fixing them in the environment.第16回 International Symposium on Environmental Biogeochemistr