This thesis consists of two parts; the first part pertains to fractoluminescence as a potential background in crystal scintillator detectors, and the second part bears on the simulation of a 24Na source to be used during the liquid scintillator phase of the SNO+ experiment. I participated in early work to develop a test-bed to study fractoluminescence in scintillators, and report here on preliminary results I obtained before I shifted my focus to SNO+. Full results obtained by the group have since been reported in PRL 111 154301 [1]. This project follows the discovery that mechanical stress on a dark matter detector’s crystals was causing a background signal. The response of inorganic crystal scintillators (Bi4Ge3O12, ZnWO4 , CdWO4 ) compressed to the point of rupture was studied. The double cleavage drilled compression geometry was used to create controlled cracks in 20×5×3 mm3 samples. A correlation between a sudden drop of the force, a burst of photonic and of acoustic emissions was discovered and a lower bound was set on the conversion efficiency from strain energy to light energy. SNO+ is a large underground experiment that aims primarily to search for neutrinoless double beta decay. The SNO+ detector consists of an acrylic vessel of liquid scintillator surrounded by light detectors. A tagged 24Na source was proposed as one of several radioactive sources to be deployed within the vessel to calibrate the detector. To achieve this an activated NaI(Tl) crystal would be coupled to a photomultiplier tube and lowered into the center of the vessel. The second half of this thesis explores options for implementing this plan and presents the detector response to a 24Na source as simulated by the Monte Carlo software developed by SNO+. The size of the crystal influences the type of information that can be gleaned from using this source so four different crystal sizes are presented for comparison. The simulations show that the source can be used to test the linearity of the energy scale and the simulation’s quenching model. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2014-06-18 17:46:15.685

La glace, le quartz, l'oxyde de magnésium ou encore les bonbons Wint-o-green (produits par Life Savers) sont quelques-uns des matériaux connus pour émettre de la lumière lors de leur fracture. Ce phénomène, appelé fractoluminescence, révèle que la fracture met en jeu des processus plus complexes que la seule création de surfaces. Ces émissions lumineuses permettent-elles d'analyser l'endommagement des matériaux, au même titre que les émissions acoustiques ? Né de l'union imprévue entre mécanique de la fracture et physique des particules, un montage expérimental a été développé pour étudier les émissions lumineuses et acoustiques lors de la fracture de scintillateurs inorganiques — matériaux couramment utilisés comme détecteurs de particules. Trois types de scintillateurs inorganiques ont été étudiés : le CdWO4, le ZnWO4, et le BGO. Il a été démontré que le CdWO4 et le ZnWO4 émettent de la lumière lors de leur fracture à pression ambiante. Des tests plus poussés ont été menés sur le BGO. Le phénomène de fractoluminescence dans le BGO a été étudié dans le cas de la fracture lente et de la fracture rapide, dans différentes conditions de pression : pression ambiante et basse pression (10−5 mbar). Dans chaque cas, des émissions lumineuses ont été observées mais elles dépendent fortement de l'environnement et des conditions de chargement de l'échantillon. Lors de la fracture lente sous vide, les émissions de lumière semblent globalement corrélées en temps à l'avancée de la fissure et aux émissions acoustiques, souvent employées en mécanique de la fracture comme indicateurs de l'endommagement. La résolution temporelle de la voie lumineuse à la nanoseconde a montré l'existence de groupes de photons pendant la fracture, à des échelles de temps inaccessibles par les méthodes acoustiques classiques. Le montage expérimental permet aussi de mesurer la quantité de lumière émise. L'énergie lumineuse lors de la fracture lente sous vide semble être proportionnelle à la surface créée. Lors de la fracture rapide sous vide, nous avons établi que 1.7 × 10−3 % de l'énergie de fracture est convertie en lumière contre au minimum 3 × 10−3 % a` pression ambiante. Cette différence montre une nouvelle fois l'importance de l'environnement et offre des pistes pour l'identification du mécanisme d'émission lumineuse / Materials such as ice, quartz, MgO or the Wint-o-green candy from Lifesavers are known to emit light during their fracture. This phenomenon, called fractoluminescence, shows that fracture is a much more complex process than the simple creation of surfaces. Do the light emissions allow to analyze material failure as the acoustic emissions ? An experimental setup is born out of the union between fracture mechanics and particle physics. It enables to study the light and acoustic emissions during fracture of inorganic scintillators — materials generally used as particle detectors. CdWO4, ZnWO4 and BGO have been tested. We demonstrated that CdWO4 and ZnWO4 emit light during their fracture at ambient pressure. More intensive tests were performed on BGO. Light emissions were studied for slow and fast crack propagation, at ambient pressure and under vacuum (10−5 mbar). In all cases, light emissions have been observed but they strongly depend on the environment and on the loading conditions. During slow crack propagation in vacuum, the light emission seems to be globally correlated in time to the crack propagation and to the acoustic emissions, which are often used in fracture mechanics as indicators of mechanical failure. The extreme time resolution of the light channel, down to the nanoseconds, shows clusters of photons during fracture, at time scales unreachable by usual acoustic methods. The experimental setup also allows to quantify the amount of light energy emitted. Light energy during slow fracture in vacuum seems to be proportional to the surface created by the crack propagation. During fast fracture in vacuum, 1.7 × 10−3 % of fracture energy is converted into light while at least 3 × 10−3 % at ambient pressure. This difference demonstrates, once again, how important the environment is, and offers leads for identifying mechanisms of light emission