Spectrométrie de neutrons rapides par bolomètres à cible lithium pour la réduction du fond des expériences de détection directe de matière noire

Fast neutron spectrometry is a common interest for both direct dark matter detection and for nuclear research centres. Fast neutrons are usually detected indirectly. Neutrons are first slowed down by moderating materials for being detected in low energy range. Nevertheless, these detection techniques are and are limited in energy resolution. A new kind of fast neutron spectroscopy has been developed at the Institut d'Astrophysique Spaciale (IAS) in the aim of having a better knowledge of neutron backgrounds by the association of the bolometric technique with neutron sensitive crystals containing Li. Lithium-6 is indeed an element which has one the highest cross section for neutron capture with the 6Li(n,)3H reaction. This reaction releases 4,78 MeV tagging energetically each neutron capture. In particular for fast neutrons, the total energy measured by the bolometer would be the sum of this energy reaction and of the incoming fast neutron energy. To validate this principle, a spectrometer for fast neutrons, compact and semi-transportable, was built in IAS. This cryogenic detector, operated at 300 - 400 mK, consists of a 0.5 g LiF 95% 6Li enriched crystal read out by a NTD-Ge sensor. This PhD thesis was on the study of the spectrometer characteristics, from the first measurements at IAS, to the measurements in the nuclear research centre of the Paul Scherrer Institute (PSI) until the final calibration with the Amande instrument of the Institut de Radioprotection et de Sûreté Nucléaire (IRSN).La spectrométrie des neutrons rapides est une technique essentielle dans plusieurs domaines notamment pour les expériences de détection d'évènements rares, telles que celles de détection directe de la matière noire, et pour les centres de recherches nucléaires. La détection des neutrons rapides se fait habituellement de manière indirecte. Les neutrons sont d'abord ralentis par des matériaux modérateurs pour être détectés ensuite dans une gamme d'énergie plus basse. Ces techniques de détection sont cependant complexes à mettre en place et sont limitées en résolution en énergie. Un nouveau type de spectrométrie de neutrons rapides a été développée à l'Institut d'Astrophysique Spatiale (IAS) dans le but d'avoir une meilleure connaissance des fonds de neutrons : il associe la technique bolométrique à des cristaux à base de lithium sensibles aux neutrons. Le lithium-6 est en effet un élément ayant une des plus grandes sections efficaces de capture neutronique avec la réaction 6Li(n,)3H. La réaction libère 4.78 MeV signant ainsi énergétiquement chaque capture de neutron et lors de l'interaction avec un neutron rapide, l'énergie totale mesurée par le bolomètre devrait être la somme de cette énergie de réaction et de l'énergie cinétique du neutron rapide incident. Afin de valider ce principe, un prototype de spectromètre à neutrons rapides, compact et semi portable, a été construit à l'IAS. Ce détecteur cryogénique, fonctionnant entre 300 et 400 mK, consiste en un cristal de 0.5 g de 6LiF enrichi à 95%, associé un thermomètre en Ge-NTD. Cette thèse a porté sur l'étude des caractéristiques de ce spectromètre, des premières mesures à l'IAS, aux mesures dans le centre de recherche de l'Institut Paul Scherrer (PSI), jusqu'au calibrage final sur l'installation Amande de l'Institut de Radioprotection et de Sûreté Nucléaire (IRSN)

Spectrométrie de neutrons rapides par bolomètres à cible lithium pour la réduction du fond des expériences de détection directe de matière noire

La spectrométrie des neutrons rapides est une technique essentielle dans plusieurs domaines notamment pour les expériences de détection d'évènements rares et pour les centres de recherches nucléaires. La détection des neutrons rapides se fait habituellement de manière indirecte. Ces techniques de détections sont souvent complexes à mettre en place et sont limitées en résolution en énergie. Un nouveau type de spectrométrie de neutrons rapides a été développée à l'Institut d'Astrophysique Spatiale associant la technique bolométrique à des cristaux à base de lithium sensibles aux neutrons. Le lithium-6 est un élément ayant une des plus grandes sections efficaces de capture neutronique avec la réaction 6Li(n,a)3H. La réaction libère 4.78 MeV signant ainsi énergétiquement la capture d'un neutron. L'énergie totale mesurée par le bolomètre devrait être la somme de cette énergie de réaction et de l'énergie d'un neutron rapide incident. Afin de valider ce principe, un prototype de spectromètre à neutrons rapides, compact et semi portable, a été construit. Ce détecteur cryogénique, fonctionnant entre 300 et 400 mK, consiste en un cristal de 0.5 g de 6LiF enrichi à 95%, associé un thermomètre en Ge-NTD. L'objectif de mon travail a été de valider le principe de spectrométrie de ce bolomètre en 6LiF dans différents champs neutroniques, de définir ses spécificités et d'établir les développements futurs en vue d'utilisations dans différents champs neutroniques.Fast neutron spectroscopy is a common interest for both direct dark matter detection and for nuclear research centres. Fast neutrons are usually detected indirectly. Neutrons are first slow down by moderating materials for being detected in low energy range. Nevertheless, these detection techniques are and are limited in energy resolution. A new kind of fast neutron spectroscopy has been developed at the Institut d'Astrophysique Spaciale (lAS) by the association of the bolometric technique with neutron sensitive crystals containing Li. Lithium-6 is indeed an element which has one the highest cross section for neutron capture with the 6Li(n,a)3H reaction. This reaction releases 4.78 MeV tagging energetically each neutron capture. The total energy measured by the bolometer would be the sum of this energy reaction and of the incoming fast neutron energy. To validate this principle, a spectrometer for fast neutrons, compact and semi-transportable, was built in lAS. This cryogenic detector, operated at 300 - 400 mK, consists of a 0.5 g LiF 95% 6Li enriched crystal read out by a NTD-Ge sens or. This PhD thesis was on the study of the spectrometer characteristics, from the fust measurements at lAS, to the measurements in the nuclear research centre of the Paul Scherrer Institute (PSI) until the final calibration with the Amande instrument of the Institut de Radioprotection et de Sûreté Nucléaire (lRSN). The goal of my work was to validate the spectroscopy principle of this 6LiF bolometer, to determine its specifications and to define the further developments for different neutron field measurements.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

EDELWEISS dark matter search: Latest results and future plans

EDELWEISS is a direct search for WIMP dark matter using cryogenic heat-and-ionization germanium detectors. We report the final results of the second stage of the experiment, EDELWEISS-II, obtained with an array of ten 400 g detectors. A total effective exposure of 384 kg.day has been achieved, obtained following fourteen months of continuous operation at the Laboratoire Souterrain de Modane. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is less than 3 events. We also present the prospects of EDELWEISS-III, which plans to accumulate more than 3000 kg.day of data with fourty new 800 g detectors

Aspherical mirrors for the Gamma-ray Cherenkov Telescope, a Schwarschild-Couder prototype proposed for the future Cherenkov Telescope Array

International audienceThe Cherenkov Telescope Array (CTA) project, led by an international collaboration of institutes, aims to create the world's largest next generation Very High-Energy (VHE) gamma-ray telescope array, devoted to observations in a wide band of energy, from a few tens of GeV to more than 100 TeV. The Small-Sized Telescopes (SSTs) are dedicated to the highest energy range. Seventy SSTs are planned in the baseline array design with a required lifetime of about 30 years. The GCT (Gamma-ray Cherenkov Telescope) is one of the prototypes proposed for CTA's SST sub-array. It is based on a Schwarzschild-Couder dual-mirror optical design. This configuration has the benefit of increasing the field-of-view and decreasing the masses of the telescope and of the camera. But, in spite of these many advantages, it was never implemented before in ground-based Cherenkov astronomy because of the aspherical and highly curved shape required for the mirrors. The optical design of the GCT consists of a primary 4 meter diameter mirror, segmented in six aspherical petals, a secondary monolithic 2-meter mirror and a light camera. The reduced number of segments simplifies the alignment of the telescope but complicates the shape of the petals. This, combined with the strong curvature of the secondary mirror, strongly constrains the manufacturing process. The Observatoire de Paris implemented metallic lightweight mirrors for the primary and the secondary mirrors of GCT. This choice was made possible because of the relaxed requirements of optical Cherenkov telescopes compared to optical ones. Measurements on produced mirrors show that these ones can fulfill requirements in shape, PSF and reflectivity, with a clear competition between manufacturing cost and final performance. This paper describes the design of these mirrors in the context of their characteristics and how design optimization was used to produce a lightweight design. The manufacturing process used for the prototype and planned for the large scale production is presented as well as the performance, in terms of geometric and optical properties, of the produced mirrors. The alignment procedure of the mirrors is also detailed. This technique is finally compared to other manufacturing techniques based on composite glass mirrors within the framework of GCT mirrors specificities

Towards final characterisation and performance of the GCT prototype telescope structure for the Cherenkov Telescope Array

International audienceThe Gamma-ray Cherenkov Telescope (GCT) is an innovative dual-mirror solution proposed for the Small-Size Telescopes of the future Cherenkov Telescope Array (CTA), capable of imaging the showers induced by cosmic gamma-rays with energies from a few TeV up to 300 TeV. The Schwarzschild-Couder design on which the telescope optical design is based makes possible the construction of a fast telescope (primary mirror diameter 4 m, focal length 2.3 m) with a plate scale well matched to compact photosensors, such as multi-anode or silicon photomultipliers (MAPMs and SiPMs, respectively) for the camera. The prototype GCT on Meudon’s site of the Observatoire de Paris saw first Cherenkov light from air showers in November 2015, using an MAPM-based camera. In this contribution, we firstly report on the prototype GCT telescope’s performance during its assessment phase. Secondly, we present the telescope configuration during a campaign of observations held in spring 2017. Finally, we describe studies of the telescope structure, such as the pointing and tracking performance

Performance of the Gamma-ray Cherenkov Telescope structure: a dual-mirror telescope prototype proposed for the future Cherenkov Telescope Array

International audienceThe Cherenkov Telescope Array (CTA) project aims to create the next generation Very High-Energy (VHE) gamma-ray telescope array. It will be devoted to the observation of gamma rays from 20 GeV to above 100 TeV. Because of this wide energy band, three classes of telescopes, associated with different energy ranges and different mirror sizes, are defined. The Small Size Telescopes (SSTs) are associated with the highest energy range. Seventy of these telescopes are foreseen on the Southern site of the CTA. The large number of telescopes constrains their mechanical structure because easy maintenance and reduced cost per telescope are needed. Moreover, of course, the design shall fulfill the required performance and lifetime in the environment conditions of the site. The Observatoire de Paris started design studies in 2011 of the mechanical structure of the GCT (Gamma-ray Cherenkov Telescope), a four-meter prototype telescope for the SSTs of CTA, from optical and preliminary mechanical designs made by the University of Durham. At the end of 2014 these studies finally resulted in a lightweight ( 8 tons) and stiff design. This structure was based on the dual-mirror Schwarzschild-Couder (SC) optical design, which is an interesting and innovative alternative to the one-mirror Davies-Cotton design commonly used in ground-based Cherenkov astronomy. The benefits of such a design are many since it enables a compact structure, lightweight camera and a good angular resolution across the entire field-of-view. The mechanical structure was assembled on the Meudon site of the Observatoire de Paris in spring 2015. The secondary mirror, panels of the primary mirror and the Telescope Control System were successfully implemented afterwards leading now to a fully operational telescope. This paper focuses on the mechanics of the telescope prototype. It describes the mechanical structure and presents its performance identified from computations or direct measurements. Upgrades of the design in the context of the preproduction and the large scale CTA production are also discussed

Final characterisation and design of the Gamma-ray Cherenkov Telescope (GCT) for the Cherenkov telescope array

The Gamma-ray Cherenkov Telescope (GCT) is one of the telescopes proposed for the Small Sized Telescope (SST) section of CTA. Based on a dual-mirror Schwarzschild-Couder design, which allows for more compact telescopes and cameras than the usual single-mirror designs, it will be equipped with a Compact High-Energy Camera (CHEC) based on silicon photomultipliers (SiPM). In 2015, the GCT prototype was the first dual-mirror telescope constructed in the prospect of CTA to record Cherenkov light on the night sky. Further tests and observations have been performed since then. This report describes the current status of the GCT, the results of tests performed to demonstrate its compliance with CTA requirements, and the optimisation of the design for mass production. The GCT collaboration, including teams from Australia, France, Germany, Japan, the Netherlands and the United Kingdom, plans to install the first telescopes on site in Chile for 2019-2020 as part of the CTA pre-production phase