Le but de l'expérience EDELWEISS est la détection directe de matière noire sousforme de WIMPs, par l'étude de leur diffusion élastique sur les noyaux de germanium des détecteurs bolomètriques. Le plus problématique des bruits de fond provient des neutrons pouvant mimer l'interaction d'un WIMP dans un détecteur. Ces neutrons sont notamment produits par les rares muons cosmiques de haute énergie qui atteignent le laboratoire souterrain malgré les 4800 m w.e. de roche. Les muons résiduels sont détectés par un système veto de 46 modules de scintillateur plastique entourant l'expérience, qui permet de rejeter la plupart du bruit de fond associé. La détermination précise du bruit de fond neutron résiduel induit par ces muons dans EDELWEISS-III, essentielle pour l'identification des WIMPs, est le but de cette thèse. Le taux de bruit de fond dépend de la géométrie de l'expérience ainsi que des matériaux utilisés, qui ont subi d'importantes modifications depuis EDELWEISS-II. Des simulations GEANT4 du passage des muons dans la nouvelle géométrie ont été réalisées afin d'extraire le taux d'événements induits par les muons dans les bolomètres. Ce taux est en bon accord avec le taux mesuré extrait des données du Run308. En parallèle, une limite inférieure sur l'efficacité du veto muon a été extraite à partir des données bolomètres. Une nouvelle méthode basée sur l'utilisation d'une source d'AmBe a été développée afin d'extraire l'efficacité de chaque module de la simulation. À partir de ces résultats, il a été montré que le bruit de fond attendu est négligeable pour la recherche de WIMPs avec les données du Run308 et ne limitera pas la sensibilité future d'EDELWEISS-III / The aim of the EDELWEISS-III experiment is to detect the elastic scattering of WIMPs from the galactic dark matter halo on germanium bolometers. The most problematic background arises from neutrons, which can mimic a WIMP interaction in a detector. Neutrons are notably induced by high energy cosmic ray muons reaching the underground laboratory despite the 4800 m w.e. of rock overburdened. Remaining muons are tagged using an active muon-veto system of 46 plastic scintillator modules surrounding the experiment, which allows to reject most of the associated background. The goal of this thesis was to give a precise estimation of the irreducible muon-induced neutron background, needed to identify a potential WIMP signal. The expected background depends on the geometry of the experiment as well as on the used materials, both strongly modified since EDELWEISS-II. Geant4-based simulations of muons through the modified geometry were performed to derive the rate of events induced by muons in the bolometer array. This rate has been shown to be in good agreement with the measured one extracted from the Run308 data. In parallel, a lower limit on the muon-veto efficiency was derived using bolometer data only. A new method based on an AmBe source was developed to extract precisely the detection efficiency of individual modules from the simulation. From these results, it was shown that the expected background is negligible for the WIMP search analyses performed with the Run308 data and won't limit the future sensitivity of the EDELWEISS-III experiment

The observed imbalance of matter and anti-matter in the universe is one of physics' most fundamental unresolved questions. The leading theories to explain this imbalance require CP violation, and the neutron electric dipole moment (nEDM) is a sensitive parameter in its determination. Many new theories of physics beyond the standard model can be constrained or ruled-out by setting limits on the nEDM. Many next generation nEDM experiments require Ultra Cold Neutrons (UCN), produced in superfluid helium. One such experiment is cryoEDM. This thesis explores various types of UCN detection technologies applicable to cryoEDM or any high-density high-efficiency cryogenic nEDM experiment. Cryogenic Phonon Scintillation detectors (CPSD) are modified for this application by operating at 500 mK, and by using a titanium transition edge sensor for phonon signal readout. A CPSD is stabilised in the transition using a novel infra-red light feedback system which reduced the response time to O</m>(100 &mu;s). The detector is characterised and calibrated using an ²⁴¹Am &alpha; source. It was found to operate reliably at this elevated temperature and measure an alpha spectrum with 11% resolution at 5.5 MeV. Scintillators are identified as a promising technology for UCN detection at low temperature. Suitable materials that are bright with fast decay times and low &gamma; sensitivity are studied in the temperature range 300 - 6 K. Their light yield to alpha excitation, their decay time characteristics and spectroscopic properties under VUV excitation are investigated. This study includes the first comprehensive investigation of the luminescence properties of plastic scintillators and of ⁶LiF/ZnS(Ag) down to 6 K. It is found that there is no degradation of the luminescence or kinetic properties of these materials across the whole temperature range, revealing them as suitable cryogenic detector materials. Using a plastic scintillator, a prototype UCN detector for operation in liquid helium is designed, manufactured and tested. It is read out using WLS optical fibres to a room temperature photomultiplier. The detector is successfully tested with cold neutrons at the ISIS neutron science facility and found to effectively measure neutrons, with a signal that is clear from background. Recommendations are made for its integration into a cryogenic neutron EDM experiment. This low-cost detector offers a promising method for the passive detection of UCN in a challenging cryogenic environment, with minimal electric interference and low background sensitivity. This technology offers the potential for improved UCN detection efficiency and thus improved sensitivity of the measurement of the neutron EDM.

Medidas da radiação gama ambiental foram feitas em algumas regiões da cidade de Ribeirão Preto-SP, de forma a contribuir para o conhecimento acerca dos níveis desse tipo de radiação no estado de São Paulo e no território brasileiro. Escolheu-se determinar as médias anuais de dose efetiva e dose efetiva coletiva, uma vez que estas grandezas levam em conta o risco de possíveis efeitos biológicos associados a exposição à radiação ionizante. Para determinar os valores dessas grandezas, os diversos setores censitários das regiões selecionadas foram mapeados e avaliados individualmente, de acordo com a taxa de dose média absorvida no ar e número de habitantes de cada setor. Utilizou-se um sistema de detecção da radiação gama baseado em cintilador plástico e GPS, que possibilitaram a medida da taxa de dose absorvida no ar a cada segundo, para as coordenadas geográficas selecionadas. Embora este sistema tenha sido desenvolvido para a detecção de fontes artificiais perdidas, ou seja, não tem o objetivo principal de fazer medidas dosimétricas da radiação gama natural, teve seus modos de leitura calibrados e comparados com resultados da literatura (com uma incerteza média de 8,7 %). Dos resultados obtidos, dos mapeamentos realizados nas regiões consideradas, as médias anuais da dose efetiva e dose efetiva coletiva para ambientes ao ar livre foram encontradas com os valores 0,034 ± 0,004 mSv/ano e 25,62 ± 9,25 homem.mSv/ano respectivamente, sendo a primeira cerca da metade da média mundial da dose efetiva recomendada pela UNSCEAR. As médias obtidas são baixas quando comparadas às encontradas em outros estudos sobre dose de radiação gama ao ar livre no estado de São Paulo e em outras regiões do território brasileiro (sendo, de 1,7 até 5,6 vezes menor). / Gamma environmental radiation measurements were done for some urban regions in the city of Ribeirão Preto-SP, in order to contribute with this knowledge on the annual ambiental values of this type of radiation in the São Paulo state and in the Brazilian territory. The quantities chosen were effective dose and effective collective dose, once they take into account the possible biologic damage related to the ionizing radiation energy absorbed. For the assessments of these quantities, selected census sectors were initially mapped out, regarding their average absorbed dose in air and the number of inhabitants living in each one of the sectors. The detector system used is based on an organic plastic scintillator and a GPS, that allows to obtain the absorbed dose rate for each second and their respective geographic coordinates. Even though this system was developed to detect missing artificial gamma sources, in other words, its main function is not for dosimetric measurements, both display modes were calibrated in exposure rate (R/h) and absorbed dose rate (Gy/h) and their readings were compared to results from the literature (with an average uncertainty of 8.7%). From the mapping results of the selected regions, the annual average effective dose and effective collective dose for outdoor environments were obtained, respectively as 0.034 ± 0.004 mSv/year and 25.62 ± 9.25 man.mSv/year. The value for the first average dose is lower (about half) than the worldwide average value published by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), also lower than the values from other regions in the national territory, regarding the gamma dose rate in outdoor environments (from 1.7 up to 5.6 times lower).

Le détecteur MINOS a été développé jusqu'à mi-2013 pour la spectroscopie γ prompte de noyaux très exotiques à partir de réactions d’arrachage de protons. Il est composé d'une cible épaisse d'hydrogène liquide pour augmenter la luminosité et d’une chambre à projection temporelle (TPC) pour reconstruire la position du vertex de réaction et de compenser l'effet de la cible épaisse sur la correction Doppler.La chambre à projection temporelle a été développée avec l'expertise du CEA-Irfu sur les détecteurs gazeux de type Micromegas. Dans un premier temps, différentes solutions pour la TPC ont été testées dans une chambre d'essai avec une source α et des mesures de rayons cosmiques. Des muons cosmiques ont été détectés pour la première fois en utilisant la chambre d'essai en début 2013 et ont validé l'utilisation d'un plan de détection Micromegas. Le premier prototype de TPC a été achevé en mai 2013 et nous avons utilisé un banc de rayons cosmiques pour estimer l’efficacité de la TPC.MINOS a ensuite été expédié au Japon et un test de performance sous faisceau a été réalisée à l'installation médicale HIMAC (Chiba, Japon) avec deux cibles minces au lieu de la cible épaisse d'hydrogène pour valider l'algorithme de reconstruction et la résolution de la position du vertex. Un algorithme de reconstruction de traces basé sur la transformée de Hough a été mis au point pour l'analyse des données, testé avec ces données, et comparé à des simulations.La première campagne de physique avec MINOS a eu lieu en mai 2014, avec SEASTAR. Elle s’est concentrée sur la première spectroscopie des ⁶ ⁶ Cr, ⁷⁰,⁷²Fe et ⁷⁸Ni. L'analyse de la spectroscopie du ⁶ ⁶Cr a révélé deux transitions, assignées aux deux premiers états excités. Une interprétation avec des calculs de modèle en couches montre que le maximum de collectivité quadripolaire se produit à N = 40 le long de la chaîne isotopique de chrome.Le ⁶ ⁶Cr est toujours placé dans la région de l’Îlot d’Inversion à N = 40 et les calculs de modèle en couches ainsi que la comparaison avec des calculs basés sur HFB suggèrent une extension de cet Îlot d’Inversion vers N = 50 en dessous du ⁷⁸Ni. L'analyse des ⁷⁰,⁷²Fe effectuée par C. Louchart (TU Darmstadt, Allemagne) révèle la même tendance que pour les isotopes de chrome. Les données et notre interprétation par le modèle en couches suggère une grande collectivité les Cr et Fe riches en neutrons, éventuellement jusqu'à N = 50, ce qui remettrait en cause la solidité de la fermeture de couche N = 50 en dessous du ⁷⁸Ni. / The MINOS device has been developed until mid-2013 for in-beam γ spectroscopy of very exotic nuclei from proton knockout reactions. It is composed of a thick liquid hydrogen target to achieve higher luminosities and a Time Projection Chamber (TPC) to reconstruct the vertex position and compensate for the thick target effect on the Doppler correction.The Time Projection Chamber has been developed with the expertise of CEA-IRFU in gas detectors and Micromegas detectors. At first, different solutions for the TPC were tested in a test chamber with an α source and cosmic-ray measurements. Cosmic rays were detected for the first time using the test chamber in early 2013 and validated the use of a Micromegas detection plane. The first TPC prototype was finished in May 2013, and we used a cosmic-ray bench to estimate the effiiciency of the TPC. The MINOS device was then shipped to Japan and an in-beam performance test was performed at the HIMAC medical facility (Chiba, Japan) with two thin targets instead of the thick hydrogen target to validate the tracking algorithm and the vertex position resolution. A tracking algorithm for the offline analysis based on the Hough transform has been developed, tested with the data, and compared with simulations.The first physics campaign using MINOS took place in May 2014 with SEASTAR. It focused on the first spectroscopy of ⁶ ⁶ Cr, ⁷⁰,⁷²Fe, and ⁷⁸Ni. The analysis of the ⁶⁶Cr spectroscopy revealed two transitions, assigned to the two first excited states. An interpretation with shell model calculations shows that the maximum of quadrupole collectivity occurs at N=40 along the Cr isotopic chain.⁶⁶Cr is still placed in the Island of Inversion region of N=40 and the shell model calculations as well as comparison with HFB-based calculations suggest an extension of this Island of Inversion towards N=50 below ⁷⁸Ni. The analysis of ⁷⁰,⁷²Fe performed by C. Louchart (TU Darmstadt, Germany) reveals the same trend as for Cr isotopes, with a maximum of deformation at N=42. The full data set and our shell-model interpretation suggests a large collectivity for neutron-rich Cr and Fe, possibly up to N=50, questioning the robustness of the N=50 shell closure below ⁷⁸Ni.

Medidas da radiação gama ambiental foram feitas em algumas regiões da cidade de Ribeirão Preto-SP, de forma a contribuir para o conhecimento acerca dos níveis desse tipo de radiação no estado de São Paulo e no território brasileiro. Escolheu-se determinar as médias anuais de dose efetiva e dose efetiva coletiva, uma vez que estas grandezas levam em conta o risco de possíveis efeitos biológicos associados a exposição à radiação ionizante. Para determinar os valores dessas grandezas, os diversos setores censitários das regiões selecionadas foram mapeados e avaliados individualmente, de acordo com a taxa de dose média absorvida no ar e número de habitantes de cada setor. Utilizou-se um sistema de detecção da radiação gama baseado em cintilador plástico e GPS, que possibilitaram a medida da taxa de dose absorvida no ar a cada segundo, para as coordenadas geográficas selecionadas. Embora este sistema tenha sido desenvolvido para a detecção de fontes artificiais perdidas, ou seja, não tem o objetivo principal de fazer medidas dosimétricas da radiação gama natural, teve seus modos de leitura calibrados e comparados com resultados da literatura (com uma incerteza média de 8,7 %). Dos resultados obtidos, dos mapeamentos realizados nas regiões consideradas, as médias anuais da dose efetiva e dose efetiva coletiva para ambientes ao ar livre foram encontradas com os valores 0,034 ± 0,004 mSv/ano e 25,62 ± 9,25 homem.mSv/ano respectivamente, sendo a primeira cerca da metade da média mundial da dose efetiva recomendada pela UNSCEAR. As médias obtidas são baixas quando comparadas às encontradas em outros estudos sobre dose de radiação gama ao ar livre no estado de São Paulo e em outras regiões do território brasileiro (sendo, de 1,7 até 5,6 vezes menor). / Gamma environmental radiation measurements were done for some urban regions in the city of Ribeirão Preto-SP, in order to contribute with this knowledge on the annual ambiental values of this type of radiation in the São Paulo state and in the Brazilian territory. The quantities chosen were effective dose and effective collective dose, once they take into account the possible biologic damage related to the ionizing radiation energy absorbed. For the assessments of these quantities, selected census sectors were initially mapped out, regarding their average absorbed dose in air and the number of inhabitants living in each one of the sectors. The detector system used is based on an organic plastic scintillator and a GPS, that allows to obtain the absorbed dose rate for each second and their respective geographic coordinates. Even though this system was developed to detect missing artificial gamma sources, in other words, its main function is not for dosimetric measurements, both display modes were calibrated in exposure rate (R/h) and absorbed dose rate (Gy/h) and their readings were compared to results from the literature (with an average uncertainty of 8.7%). From the mapping results of the selected regions, the annual average effective dose and effective collective dose for outdoor environments were obtained, respectively as 0.034 ± 0.004 mSv/year and 25.62 ± 9.25 man.mSv/year. The value for the first average dose is lower (about half) than the worldwide average value published by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), also lower than the values from other regions in the national territory, regarding the gamma dose rate in outdoor environments (from 1.7 up to 5.6 times lower).

科学研究費補助金 研究種目:基盤研究(C)(2) 課題番号:09680476 研究代表者:青山 隆彦 研究期間:1997-1999年度