<p>The application of pulse shape analysis (PSA) and γ-ray tracking techniques has attracted a great deal of interest in the recent years in fields ranging from nuclear structure studies to medical imaging. These new data analysis methods add position sensitivity as well as directional information for the detected γ-rays to the excellent energy resolution of germanium detectors. This thesis focuses on the application of PSA on planar segmented germanium detectors, divided into three separate studies. The pulse shape analysis technique known as the matrix method was chosen due to its ability to treat events with arbitrary number and combinations of interactions within a single detector. It has been applied in two experiments with the 25-fold segmented planar pixel detector -- imaging and polarization measurements -- as well as in a simulation of upcoming detectors for DESPEC at NuSTAR/FAIR.</p><p>In the first experiment, a point source of ¹³⁷Cs was imaged. Events where the 662 keV γ-rays scattered once and were then absorbed in a different segment were treated by the PSA algorithm in order to find the locations of these interactions. The Compton scattering formula was then used to determine the direction to the source. The experiment has provided a robust test of the performance of the PSA algorithm on multiple interaction events, in particular those with interactions in adjacent segments, as well as allowed to estimate the realistically attainable position resolution. In the second experiment, the response of the detector to polarized photons of 288 keV was studied. The polarization of photons can be measured through the observation of the angular distribution of Compton-scattered photons, Hence the ability to resolve the interaction locations had once again proven useful.</p><p>The third study is focused on the performance of the proposed planar germanium detectors for the DESPEC array. As these detectors have not yet been manufactured at the time of this writing, a set of data simulated in GEANT4 was used. The detector response was calculated for two of the possible segmentation patterns -- that with a single pixelated contact and one where both contacts are segmented into mutually orthogonal strips. In both cases, PSA was applied in order to reconstruct the interaction locations from this response. It was found that the double-sided strip detector can achieve an over-all better position resolution with a given number of readout channels. However, this comes at the expense of a small number of complex events where the reconstruction fails. These results have also been compared to the performance of the 25-fold pixelated detector.</p>

This report describes investigations of the NE213-detector and the possibility to utilize pulse shape analysis to separate neutrons and gammas in a mixed emission field. Neutron fluxes are often contaminated with gammas, to which the detectors are sensitive. Sorting out the unwanted gamma pulses from the interesting neutrons is therefore crucial in many situations, for instance in fusion reactor diagnostics, such as for neutron cameras. This can be done based on pulse shapes, which differ for gammas and neutrons interacting in the NE213-detector. By analyzing the pulse shapes from a digital transient recorder, neutrons can be distinguished from gammas. An experiment with a Cf-252 neutron source was set up and provided data. The separation algorithm was based on charge comparison and gave good results. Furthermore the results of the pulse shape analysis were verified by TOF-measurements. The lowest permissible energy for a reasonable separation was found to be around 0.5 MeV. Some conclusions on the limitations of the equipment were also made.

Nuclear physics experiments typically involve the collection and analysis of detector signals produced by the interaction of subatomic particles with matter to deduce various quantities. When heavy ions are involved, Si Detector signals are distorted by the formation of a plasma-like cloud from the interaction between the heavy ions and the detector material. The signal amplitude is reduced and delayed, two effects known as Pulse Height Defect (PHD) and Plasma Delay Time (PDT). A recent experiment was performed at the Institut Laue-Langevin(ILL) experimental nuclear reactor facility in Grenoble, using the LOHENGRIN mass spectrometer, to study these walk effects. The purpose of this project is to use a subset of the data to perform pulse shape analysis and develop a parametrization of the pulse waveform in order to better understand the PDT and PHD and how the pulses are affected. Initially, the PDT and PHD are estimated for masses 90, 100, 130 and 143 u using already established methods. The pulse waveforms are then investigated and a suitable parametrization of the pulse waveform is developed. The region around the pulse onset, which is important in extracting the timing characteristics of the pulse, is found to be described rather well by the Landau function. The Landau function parameters are further investigated and correlations with pulse shape characteristics are discussed. Finally, this novel parametrization is used as an alternative approach to estimate the PDT for the same masses as initially. Comparisons between the two methods indicate that the PDT is actually a combined effect of the physical plasma delay and the walk effects introduced by the underlying triggering routine that is used during offline analysis.

The application of pulse shape analysis (PSA) and γ-ray tracking techniques has attracted a great deal of interest in the recent years in fields ranging from nuclear structure studies to medical imaging. These new data analysis methods add position sensitivity as well as directional information for the detected γ-rays to the excellent energy resolution of germanium detectors. This thesis focuses on the application of PSA on planar segmented germanium detectors, divided into three separate studies. The pulse shape analysis technique known as the matrix method was chosen due to its ability to treat events with arbitrary number and combinations of interactions within a single detector. It has been applied in two experiments with the 25-fold segmented planar pixel detector -- imaging and polarization measurements -- as well as in a simulation of upcoming detectors for DESPEC at NuSTAR/FAIR. In the first experiment, a point source of 137Cs was imaged. Events where the 662 keV γ-rays scattered once and were then absorbed in a different segment were treated by the PSA algorithm in order to find the locations of these interactions. The Compton scattering formula was then used to determine the direction to the source. The experiment has provided a robust test of the performance of the PSA algorithm on multiple interaction events, in particular those with interactions in adjacent segments, as well as allowed to estimate the realistically attainable position resolution. In the second experiment, the response of the detector to polarized photons of 288 keV was studied. The polarization of photons can be measured through the observation of the angular distribution of Compton-scattered photons, Hence the ability to resolve the interaction locations had once again proven useful. The third study is focused on the performance of the proposed planar germanium detectors for the DESPEC array. As these detectors have not yet been manufactured at the time of this writing, a set of data simulated in GEANT4 was used. The detector response was calculated for two of the possible segmentation patterns -- that with a single pixelated contact and one where both contacts are segmented into mutually orthogonal strips. In both cases, PSA was applied in order to reconstruct the interaction locations from this response. It was found that the double-sided strip detector can achieve an over-all better position resolution with a given number of readout channels. However, this comes at the expense of a small number of complex events where the reconstruction fails. These results have also been compared to the performance of the 25-fold pixelated detector. / QC 20101110

In this work, Neutron Depth Profiling (NDP) analysis capability has been added to the Oregon State University TRIGA�� Reactor Prompt Gamma Neutron Activation Analysis Facility (PGNAA). This system has been implemented with an advanced digital spectroscopy system and is capable of rise time pulse shape analysis as well as coincidence measurements from multiple detectors. The digital spectroscopy system utilizes a high-speed multichannel digitizer with speeds up to 200 Megasamples/second (MS/s) with advanced hardware trigger and time stamping capabilities. These additions allow the facility to conduct simultaneous NDP and PGNAA combined measurements, which also enables cross calibration. The digital pulse processing is implemented with software programmed rise time pulse shape analysis capabilities for the analysis of the detector responses on a pulse-by-pulse basis to distinguish between different interactions in the detector. The advanced trigger capabilities of the digitizer were configured to accurately measure and correct for dead time effects from pulse pile up and preamplifier decay time. / Graduation date: 2013

Le noyau est généralement décrit comme un ensemble de protons et de neutrons liés dans un potentiel de champ moyen. Cependant afin d'obtenir une meilleure description, il convient de tenir compte des interactions locales dont principalement l'appariement. Les appariements neutron-neutron et proton-proton sont assez bien étudiés alors que ce n'est pas le cas de l'appariement neutron-proton. Celui-ci peut être soit isovectoriel similaire à l'appariement nn/pp, soit isoscalaire et donc dans ce cas vraiment méconnu. La surliaison des noyaux N=Z pourrait être une manifestation de l'appariement np.Nous avons effectué l'étude de l'appariement np par réactions de transfert de paires np. Dans ce cas il est attendu que la section efficace de transfert de paires np soit augmentée en présence d'un appariement np important. L'appariement np devrait être important dans les noyaux N=Z avec des orbitales de J élevé. Or, des faisceaux de ces noyaux ne sont accessibles que depuis le développement des installations de faisceaux radioactifs.Nous avons effectué notre expérience au GANIL (Caen) avec un montage permettant une détection des produits issus de la réaction de transfert (p, ³ He). Cette réaction met en jeu à la fois des paires np isovectorielles et isoscalaires. Nous avons utilisé des faisceaux de ⁵⁶ Ni et de ⁵²Fe permettant d'observer l'évolution de l'appariement np avec l'occupation de la couche 0f7/2.Tout d'abord, nous avons analysé les données issues de la réaction ⁵⁶Ni(p,d)⁵⁵Ni et extrait des résultats que nous avons comparé à ceux existants. Cette démarche a permis de valider la procédure d'analyse des données.Après analyse des données issues de la réaction ⁵⁶Ni(p,3He)⁵⁴Co, nous avons extrait les populations des états du ⁵⁴Co qui donnent des informations sur l'intensité relative des deux types d'appariement np pour le noyau ⁵⁶Ni et montrent que l'appariement np isovectoriel est dominant dans ce noyau.De plus, dans le cadre d'un développement d'un futur détecteur de particules chargées, un travail de R&D sur la discrimination des particules légères par la forme des signaux a été réalisé et est présenté. / A nucleus is described as a set of independent neutrons and protons linked by a mean-field potential. However, in order to have a better description one needs to take in account some residual interactions such as pairing. Neutron-neutron and proton-proton pairings are well-studied but neutron-proton pairing is not well-known. np pairing can be isovector pairing such as nn and pp pairing or isoscalar which is yet unknown. Overbinding of N=Z nuclei could be a manifestation of np pairing.We have studied np pairing through transfer reactions. In this case, the cross-section of np pair transfer is expected to be enhanced in the presence of important np pairing. np pairing is expected to be important in N=Z nuclei with high J orbitals. Since the development of radioactive beam facilities, such beams are only available.The experiment was performed at GANIL with an efficient set-up so as to detect products from the (p,³He) transfer reaction. This reaction is affected by isovector and isoscalar np pairing. We used ⁵⁶Ni and ⁵²Fe beams so as to see the effect of the occupancy of 0f7/2 shell on the np pairing.First, we analysed the data from the ⁵⁶Ni(p,d)⁵⁵Ni reaction and we compared the results with the literature to validate analysis procedure.After analysing data from the ⁵⁶Ni(p,3He)⁵⁴Co reaction and extracting the population of the various states of ⁵⁴Co, we obtained information about the relative intensity between isoscalar and isovector np pairing in ⁵⁶Ni showing the predominance of isovector np pairing in this nucleus .Moreover, in the framework of developing a new charged particle detector, R&D on the discrimination of light nuclei using pulse shape analysis was performed and is presented.

Failed fuel refers to the breach in the fuel-clad of an irradiated fuel assembly in a nuclear reactor. Neutron detection or gamma detection is commonly used in Failed Fuel Detection and Locating (FFDL) system to monitor the activity of the coolant. Though these methods offer specific advantages under different conditions of the coolant, providing both types of detectors in FFDL system is impractical. This limitation is the motivation for the detector system developed in the present work. In the present work, effort has been made for realising a detector system for simultaneous measurement of neutron and gamma activity of the coolant, thus offering a two-parameter basis for failed fuel detection. NE213 liquid scintillator was chosen for this work as it has good detection capability for both neutrons and gammas. Additionally, the neutrons and gammas interacting with NE213 detector can be separated based on pulse shape discrimination. The work reported in this thesis includes fabrication details and different steps followed in assembling the NE213 detector. Details of experimental set-up developed for pulse height analysis and pulse shape analysis are covered. Results of experiments carried out to study the response of the NE213 detector to gamma and neutron sources using pulse height analyser are presented. The absolute gamma efficiency and relative gamma efficiency of NE213 detector are calculated. Neutron–gamma separation capability of NE213 detector based pulse shape analysis system is reported. Application of the developed detector system to analyse the coolant activity in FFDL system in a reactor is described. Response of the detector is compared with the existing FFDL system at different power levels of the reactor. Since failed fuel is a rare event, it was simulated using neutron and gamma sources. Pulse shape analysis spectra obtained under simulated failed fuel condition are presented.

L’apparition de la segmentation électrique des détecteurs au GeHP et de l’électronique numérique a ouvert la voie à des applications prometteuses, telles que le tracking γ, l’imagerie γ ou la mesure bas bruit de fond, pour lesquelles une connaissance fine de la réponse du détecteur est un atout. L’IPHC a développé une table de scan utilisant un faisceau collimaté, qui sonde la réponse d’un détecteur dans tout son volume en fonction de la localisation de l’interaction. Elle est conçue pour utiliser une technique innovante de scan 3D, le Pulse Shape Comparison Scan, qui a été d’abord simulée afin de démontrer son efficacité. Un détecteur AGATA a été scanné de manière approfondie. Des scan 2D classiques ont permis, entre autres, de mettre en évidence des effets locaux de modification de la collection des charges, liés à la segmentation. Pour la première fois, une base de données 3D, complète, de formes d’impulsions fonction de la position d’interaction a été établie. Elle permettra notamment d’améliorer les performances du spectromètre AGATA. / Recent developments of electrical segmentation of HPGe detectors, coupled with digital electronics have led to promising applications such as γ-ray tracking, γ-ray imaging or low-background measurements which will benefit from a fine knowledge of the detector response. The IPHC has developed a new scanning table which uses a collimated γ-ray beam to investigate the detector response as a function of the location of the γ-ray interaction. It is designed to use the Pulse Shape Comparison Scan technique, which has been simulated in order to prove its efficiency. An AGATA detector has been thoroughly scanned. 2D classical scans brought out, for example, local charge collection modification effects such as charge sharing, due to the segmentation. For the first time, a 3D, complete pulse-shape database has been established. It will especially allow to improve the overall AGATA array performances.

CdZnTe-Detektoren, zur direkten Messung von Gammastrahlung, die bei der Behandlung mit beschleunigten Teilchen entsteht, besitzen das Potential eine Reichweitenkontrolle zu ermöglichen und die Strahlendosis zu erfassen. Jedoch stellt die Identifizierung einzelner, energetisch nahe beieinander liegenden Photonenenergien, bei einem solchen Volumendetektor eine besondere Herausforderung dar. Die vorliegende Arbeit beschäftigt sich mit der Entwicklung von Methoden zur Korrektur der Signalformen am Volumenhalbleiter CdZnTe und der damit verbundenen Verbesserung der Energie- und Zeitinformation des Detektors. Dies ist wichtig für den Einsatz in der therapeutischen Medizin mit beschleunigten Teilchen, da Ladungsträger durch Gammastrahlung in unterschiedlichen Tiefen des Detektors generiert werden und einen tiefenabhängigen Fehler in der Detektorgenauigkeit erzeugen. / CdZnTe detectors, used for the direct measurement of gamma radiation generated during the treatment with accelerated particles, have the potential to provide a range control and to detect the radiation dose. However, the identification of individual energetically close photon energies in such a volume detector is a particular challenge. The present work deals with the development of methods for correcting the signal forms of the CdZnTe and the associated improvement of the energy and time information of the detector This is important for use in accelerated particle medicine because charge carriers are generated by gamma radiation at different depths of the detector and produce a depth dependent error in detector accuracy.

EDELWEISS est une expérience de détection directe de matière noire froide non-baryonique sous forme de particules massives et faiblement interagissantes (connues sous l'acronyme de WIMPs), qui constituent actuellement les candidats les plus populaires pour rendre compte de la masse manquante de l'Univers. Dans ce but, EDELWEISS utilise des bolomètres de germanium opérés à température cryogénique (20 mK environ) dans le Laboratoire Souterrain de Modane (LSM) à la frontière franco-italienne. En particulier, depuis 2008, un nouveau type de détecteur est en fonctionnement, équipé d'électrodes concentriques pour optimiser le rejet des évènements de surface (détecteurs à grilles coplanaires). Cette thèse se décompose en plusieurs axes de recherche. Tout d'abord, nous avons réalisé des mesures concernant la collecte des charges dans les cristaux. Les lois de vitesse des porteurs (électrons et trous) ont été déterminées dans le germanium à 20 mK dans la direction <100>, et une étude complète de la répartition des charges a été menée, avec une évaluation de l'anisotropie du transport et de la diffusion transverse des porteurs. Ces résultats permettent d'avoir une meilleure compréhension du fonctionnement interne des détecteurs d'Edelweiss. Ensuite, des études portant sur l'amélioration des performances ont été effectuées. Nous avons en particulier permis d'optimiser la procédure de régénération des cristaux et améliorer le rejet passif des évènements de surface (β). Le volume utile de détection des détecteurs a été évalué en utilisant les raies de deux radio-isotopes activés cosmiquement, le 68Ge et le 65Zn. Enfin, une étude exhaustive portant sur l'étude des spectres à basse énergie a été menée, ce qui permet de mettre au point une méthode d'analyse systématique pour la recherche de WIMPs de basse masse dans EDELWEISS. / EDELWEISS is a direct non-baryonic cold dark matter detection experiment in the form of weakly interacting massive particles (also known as WIMPs), which currently constitute the most popular candidates to account for the missing mass in the Universe. To this purpose, EDELWEISS uses germanium bolometers at cryogenic temperature (20 mK approximately) in the Underground Laboratory of Modane (LSM) at the French-Italian border. Since 2008, a new type of detector is operated, equipped with concentric electrodes to optimize the rejection of surface events (coplanar-grid detectors). This thesis work is divided into several research orientations. First, we carried out measurements concerning charge collection in the crystals. The velocity laws of the carriers (electrons and holes) have been determined in germanium at 20 mK in the <100> orientation, and a complete study of charge sharing has been done, including an evaluation of the transport anisotropy and of the straggling of the carriers. These results lead to a better understanding of the inner properties of the EDELWEISS detectors. Then, studies relating to the improvement of the performances were carried out. In particular, we have optimized the space-charge cancellation procedure in the crystals and improved the passive rejection of surface events (β). The fiducial volume of the detectors has been evaluated using two X-ray lines from cosmically activated radionuclides: 68Ge and 65Zn. Lastly, an exhaustive study of the low energy spectra has been carried out, which makes it possible to develop a systematic analysis method for the search of low-mass WIMPs in EDELWEISS.