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Le temps de vie du neutron libre joue un rôle important dans la physique des particules comme dans des modèles cosmologiques. Notre connaissance de la valeur précise du temps de vie du neutron est limitée par les incertitudes systématiques des deux méthodes expérimentales couramment utilisées, les méthodes dites de "faisceau" et de "bouteille matérielle". En outre une déviation systématique des valeurs de temps de vie obtenues par les deux méthodes s'est manifestée au cours des dernières décennies.Le projet HOPE fait parti d'une nouvelle génération d'expériences qui cherchent à mesurer le temps de vie du neutron en stockant des neutrons ultra-froids (UCN) dans un potentiel magnéto-gravitationnel. HOPE génère les champs magnétiques nécessaires par une combinaison d'aimants permanents puissants de terre rare, qui produisent des champs magnétiques maximaux d'environ 1.3 T, et un système de bobines supraconductrices. Dans cette thèse je donnerai une description détaillée de l'appareil, des effets systématiques possibles et comment nous envisageons d'étudier et de maîtriser ces effets. Ensuite les résultats d'un premier temps de faisceau, effectué à la source PF2, vont être présentés et discutés. Les résultats sont encourageants puisque nous avons atteint des constants de temps de stockages maximaux de 881(46) s, ce qui indique des pertes d'UCN très faibles pendant la phase du stockage. / The lifetime of the free neutron plays an important role in fundamental particle physics as well as cosmological models. Our knowledge of the precise value of the neutron lifetime is limited by the systematical inaccuracies of the two commonly used experimental approaches, the so called “beam” and “material bottle” methods. Moreover a systematic deviation of the lifetime-values extracted from both methods has become manifest over the past decades.The HOPE project is part of a new generation of experiments that aims to determine the neutron lifetime by storing ultra cold neutrons (UCN) in a combined magneto-gravitational potential. HOPE generates the necessary gradient magnet fields by a combination of highly potent rare-earth permanent magnets with a maximum B-field strength of about 1.3 T and a set of superconducting coils. In this thesis I give a detailed description of the apparatus, possible systematical effects and how we are planning to investigate and cope with those effects. Subsequently the results from a first beamtime at the PF2 source will be presented and discussed. The results are encouraging as we reached a maximum storage-time constants of 881(46) s, indicating a very small UCN loss rate during storage.

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Made available in DSpace on 2014-10-09T12:48:41Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:45Z (GMT). No. of bitstreams: 1 09250.pdf: 2620343 bytes, checksum: 7c7a04350dced4d288c23f2472f9b667 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Digitized by Kansas State University Libraries

Call number: LD2668 .T4 1961 N37

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / Two types of high efficiency neutron detector arrays (HENDAs), a 32-channel planar device and two trenched devices, were constructed at Kansas State University (KSU) and characterized. These HENDAs are prototypes for a detector that will be developed for the Spallation Neutron Source (SNS), which is located at Oak Ridge National Laboratory (ORNL). The general design objectives of a proposal from the KSU Semiconductor Materials and Radiological Technologies (SMART) Lab to the National Science Foundation, which led to a grant that funded this research, were reached. A spatial resolution for the HENDA prototypes of approximately 120 μm was achieved. The prototypes had relatively fast response times of approximately 1.2 μs, with rise times of 300 ns for the planar device and 200 ns for the 100-μm deep trenched device. The thermal neutron counting efficiency of one of the trenched devices was measured to be about 12%. It is expected that the goal of a 50% efficient HENDA is attainable by making trenches contained within the trenched device deeper and by stacking modules in a sandwich design. The pulse heights produced by the HENDA prototypes were approximately 0.5 volt with noise levels of 13 mvolt, resulting in a signal to noise ratio of almost 40:1. The response of HENDA, when placed in the neutron beam from the tangential beam port of the KSU TRIGA Mark II was proportional to the reactor power from 2 kW to 512 kW. At 512 kW, the neutron flux is φ = 1.08x10[superscript]7 cm[superscript]-2 s[superscript]-1, and therefore HENDA can operate with negligible dead time at neutron fluxes beyond 107 cm-2 s-1. From the experimental results, HENDA is a valuable linear array detector and can be applied to experiments that are designed to study material properties and structures through methods such as neutron diffraction and imaging.

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / Improvised explosives devices (IEDs) are the cause of many casualties worldwide. Current methods for detecting IEDs are insufficient. A signature-based scanning technique based upon the fact that explosives consist primarily of hydrogen, oxygen, nitrogen, and carbon is examined as a possible rapid, standoff method for detecting IEDs. Devices employing this method rely on a template-matching technique in which the detector responses acquired through neutron and photon interrogation are compared to responses from a known explosive. A figure-of-merit is calculated to determine how well the template and the unknown match. This thesis explores the feasibility of employing the neutron interrogation aspect of this method.

A new method for generating initial data for simulations of neutron stars in binary systems. The construction of physically relevant initial data is crucial to accurate assessment of gravitational wave signals relative to theoretical predictions. This method builds upon the Bowen-York curvature for puncture black holes. This data is evolved and compared against simulations in the literature with respect to orbital eccentricity, merger and collapse times, and emitted energy and angular momentum. The data exhibits some defects, including large central density oscillations in stars and center of mass drift in unequal-mass systems. Some approaches for improvements in potential future work are discussed.