Two aspects of applied nuclear physics have been studied in this thesis; Monte Carlo simulations for high-sensitivity monitoring of radioactive xenon and high-accuracy neutron-proton scattering measurements for neutron physics applications and fundamental physics. The Monte Carlo simulations have been performed for two systems for detection of radioactive xenon, using the MCNP code. These systems, designed for monitoring of violations of the Comprehensive Nuclear-Test-Ban Treaty, are based on coincident detection of electrons and gamma rays, emitted in beta decay of xenon nuclides produced in nuclear weapons explosions. In general, the simulations describe test data well, and the deviations from experimental data are understood. The neutron-proton scattering measurements have been performed by measuring the differential np scattering cross section at 96 MeV in the angular range θc.m.= 20° – 76°. Together with an earlier data set at the same energy, covering the angles θc.m.= 74° – 180°, a new data set has been formed in the angular range θc.m.= 20° – 180°. This extended data set has been normalised to the experimental total np cross section, resulting in a renormalisation of the earlier data of 0.7 %, which is well within the stated normalisation uncertainty for that experiment. The results on forward np scattering are in reasonable agreement with theory models and partial wave analyses and have been compared with data from the literature.

A beam of 250A MeV 17O ions was scattered from argon and xenon targets. The large excess of fast neutrons compared with statistical model calculations that was observed earlier for xenon, was confirmed and found for argon as well. Analysis and calculations show that a considerable fraction of these neutrons can be interpreted as coming from direct knock-out reactions. The angular distributions do not support the suggestion of using fast heavy ion scattering as a probe for the study of the neutron skin in nuclei. While the basic idea that a heavy projectile tends to sample the neutron wave function near the surface of the nucleus is sound, the measured neutron distribution is not as distinct as suggested by the previous experiment. This makes it difficult to distinguish direct reactions from other channels, such as semi-direct decay of giant resonances. The improvements in the experimental methods have made the concept of using the CELSIUS storage and cooler ring as an internal magnetic spectrometer attractive for other of experiments presently being prepared.

Data on elastic scattering of 96 MeV neutrons from 56Fe, 89Y and 208Pb in the angular interval 10-70° are presented. The previously published data on 208Pb have been extended, as a new method has been developed to obtain additional information at the most forward angles. The results are compared with phenomenological and microscopic optical potentials. The theory predictions are in general in good agreement with the experimental data. A study of the deviation of the zero-degree cross section from Wick's limit has been performed. The data on 208Pb are in agreement with Wick's limit, while those on lighter nuclei overshoot the limit significantly. A novel analysis method has been developed to obtain the inelastic neutron emission cross sections from the existing 56Fe data. The method is based on folding a trial spectrum with the response of the detector setup. The data cover the angular interval 26-65° and an excitation energy range of 0-45 MeV, ranges hitherto not studied. The results are compared with nuclear model predictions and found to be in good agreement with the experimental data.

No description available.

Les méthodes perturbatives, telle que l’approximation de Born, sont nécessaires pour résoudre les problèmes inhérents à l’ionisation d’atomes et de molécules par impact d’électrons ou de positrons. Afin d’optimiser les calculs nécessaires pour le second terme de l’approximation de Born, nous avons commencé par étudier l’ionisation de l’atome le plus simple : celui d’hydrogène. Nous avons utilisé une base contenant un grand nombre d’états (294) nous permettant d’éviter la relation de fermeture qui nécessite l’introduction d’un paramètre qui représente la valeur moyenne d’excitation. Nos résultats ont montré un bon accord avec l’expérience surtout pour les faibles énergies des électrons éjectés. Nous avons ainsi pu montrer l’importance de la contribution des états du continuum (représentés par des pseudo-états), en particulier pour les transitions de type dipolaire. Pour la double ionisation de l’atome d’hélium, nous avons appliqué la même méthodologie de calcul numérique complet tout en incluant 20 états et pseudo-états intermédiaires et en utilisant une fonction d’onde corrélée d’interaction de configuration, on a trouvé pour les grandes énergies d’incidence (5 keV) que l’effet du terme Born 2 est presque nul. Par contre l’application de « SBA » avec la relation de fermeture pour l’état fondamental et les premiers états excités montre une petite différence avec « FBA » en particulier en dehors de la région du transfert. Dans le cas des faibles énergies d’incidence (601 eV) il était attendu d’obtenir un effet important de « SBA » surtout que des études sur les (e,3-1e) de l’hélium montrent un déplacement du pic principal par rapport à « FBA ». Donc on peut dire que les 20 états intermédiaires contribuent de façon insuffisante et qu’il faudra considérer beaucoup plus d’états / The perturbative methods, such as Born approximation, are necessary to solve the problems concerning the ionization of atoms and molecules by electrons or positrons impacts. In order to use Born approximation in an optimized way, we tested it on the simplest atom « Hydrogen » by using a basis of large amount of intermediate states (294) and complete numerical calculation without using the closure approximation whose application needs the introduction of a parameter which is the excitation mean value. Our results proved a significant agreement with the experiment particularly for small energies of the ejected electrons. We also proved an important contribution of the continuum (represented by the pseudo-states), and particularly the dipolar transition. For the double ionization of Helium atom, we applied the same methodology of complete calculation by including 20 intermediate states and pseudo-states and by using a configuration interaction wave function, we found that for high incident energy (5 keV) the effect of the second term of Born is almost zero. However, the application of the « SBA » with the closure approximation by using the fundamental state and the first excited states show a slight difference relative to the « FBA » particularly outside the transfer region. In case of low incident energy (601 eV), it was expected a crucial effect of the « SBA » especially that previous studies of (e, 3-1e) of Helium show a significant shift of the main peak relative to the « FBA ». So we can say that 20 intermediate states are not enough and the application of the « SBA » needs more states

Electromagnetic processes induced by electron scattering off few-nucleon systems are theoretically investigated in the non-relativistic formalism. Non-relativistic one-body nuclear current operators are used with a parametrization of nucleon electromagnetic form factors based on recent experimental nucleon scattering data. Electromagnetic form factors of three-nucleon and four-nucleon systems are calculated from elastic electron-nucleus scattering information. Nuclear response functions used in the determination of differential cross sections for inclusive and exclusive quasi-elastic electron-nucleon scattering from the 4He nucleus are also calculated. Final-state interactions in the quasi-elastic nucleon knockout process are explicitly taken into account using the Glauber approximation. The sensitivity of the response functions to the final-state interactions is investigated. The Antisymmetrized Molecular Dynamics approach with angular momentum and parity projection is employed to construct ground state wave functions for the nuclei. A reduced form of the realistic Argonne V18 nucleon-nucleon potential is used to describe nuclear Hamiltonian. A convenient numerical technique of approximating expectation values of nuclear Hamiltonian operators is employed. The constructed wave functions are used to calculate ground-state energies, root-mean-square radii and magnetic dipole moments of selected light nuclei. The theoretical predictions of the nuclear properties for the selected nuclei give a satisfactory description of experimental values. The Glauber approximation is combined with the Antisymmetrized Molecular Dynamics to generate wave functions for scattering states in quasi-elastic scattering processes. The wave functions are then used to study proton knockout reactions in the 4He nucleus. The theoretical predictions of the model reproduce experimental observation quite well. / Physics / Ph D. (Physics)

In this work, different double ionization (DI) mechanisms of various atomic and molecular targets by electron impact at different intermediate incident energies have been studied by so-called (e, 3-1e) and (e, 3e) experiments. Four and five fold differential cross sections in angle and in energy have been measured and analyzed in a coplanar geometry. The experimental measurements are compared with both first order and second order theoretical model calculations. The results shows that the theories including second order mechanism (such as Two Step 2, TS2) are generally in better agreement with the experimental data than these only including first order mechanisms (such as Shake Off and Two Step 1). This demonstrates that under present kinematics, second order mechanism plays an important role or even dominates over first order mechanisms. Besides, all DI results are compared with the predictions of TS2 kinematical analysis developed by Lahmam-Bennani et al (2010). Most of the structures shown in the measured angular distribution can be correctly explained by the TS2 kinematical analysis predictions. Besides, we extend this model by including the recoil contribution in each step. Some structures which cannot be explained by the previous model are well explained by the extended TS2 kinematical model. The isoelectronic target structure influence in DI is investigated preliminarily. The (e, 3-1e) results on Ne and CH₄ indicate the differences under same kinematics. The data analysis is underway.

Electromagnetic processes induced by electron scattering off few-nucleon systems are theoretically investigated in the non-relativistic formalism. Non-relativistic one-body nuclear current operators are used with a parametrization of nucleon electromagnetic form factors based on recent experimental nucleon scattering data. Electromagnetic form factors of three-nucleon and four-nucleon systems are calculated from elastic electron-nucleus scattering information. Nuclear response functions used in the determination of differential cross sections for inclusive and exclusive quasi-elastic electron-nucleon scattering from the 4He nucleus are also calculated. Final-state interactions in the quasi-elastic nucleon knockout process are explicitly taken into account using the Glauber approximation. The sensitivity of the response functions to the final-state interactions is investigated. The Antisymmetrized Molecular Dynamics approach with angular momentum and parity projection is employed to construct ground state wave functions for the nuclei. A reduced form of the realistic Argonne V18 nucleon-nucleon potential is used to describe nuclear Hamiltonian. A convenient numerical technique of approximating expectation values of nuclear Hamiltonian operators is employed. The constructed wave functions are used to calculate ground-state energies, root-mean-square radii and magnetic dipole moments of selected light nuclei. The theoretical predictions of the nuclear properties for the selected nuclei give a satisfactory description of experimental values. The Glauber approximation is combined with the Antisymmetrized Molecular Dynamics to generate wave functions for scattering states in quasi-elastic scattering processes. The wave functions are then used to study proton knockout reactions in the 4He nucleus. The theoretical predictions of the model reproduce experimental observation quite well. / Physics / Ph D. (Physics)

No description available.

Dans ce travail, différents mécanismes conduisant à la double ionisation de plusieurs cibles atomiques ou moléculaires par impact d’électrons d’énergie incidente moyenne (600-700 eV) sont étudiés par des expériences de coïncidence dites (e, 3-1e) et (e, 3e). Dans ces expériences, les sections efficaces quadruplement et quintuplement différentielles en angles et en énergies ont été mesurées et analysées dans une géométrie coplanaire. Les résultats expérimentaux sont comparés à ceux obtenus par des calculs théoriques utilisant des modèles aussi bien du premier ordre que du second ordre. La comparaison montre que les théories incluant les mécanismes de second ordre (tel que Two Step 2, TS2) sont en meilleur accord avec l’expérience que ceux incluant uniquement les mécanismes de premier ordre (tels que Shake Off et Two Step 1). Ceci démontre que, dans nos conditions cinématiques, les mécanismes de second ordre jouent un rôle important, voire même dominant par rapport aux mécanismes de premier ordre. Par ailleurs, l’ensemble de nos résultats de double ionisation sont compares aux prédictions d’un modèle ‘TS2-cinématique’ développé par Lahmam-Bennani et al (2010), et qui consiste à considérer le processus de double ionisation comme deux événements successifs de simple ionisation (e,2e). La plupart des structures observées dans les distributions angulaires des électrons éjectés ont pu être interprétées et expliquées par ce modèle ‘TS2-cinématique’. Nous avons également étendu ce modèle en tenant compte de la contribution de la diffusion de recul dans chacune des étapes (e,2e). Certaines structures qui étaient restées inexpliquées par « l’ancien » modèle le sont maintenant par le modèle ‘TS2-cinématique’ étendu. L’influence de la structure atomique versus moléculaire de la cible dans le processus de double ionisation a fait l’objet d’une étude préliminaire. Les résultats (e, 3-1e) des cibles iso électroniques Ne et CH₄ montrent certaines différences pour les mêmes conditions cinématiques. L’analyse plus approfondie de ces données est en cours. / In this work, different double ionization (DI) mechanisms of various atomic and molecular targets by electron impact at different intermediate incident energies have been studied by so-called (e, 3-1e) and (e, 3e) experiments. Four and five fold differential cross sections in angle and in energy have been measured and analyzed in a coplanar geometry. The experimental measurements are compared with both first order and second order theoretical model calculations. The results shows that the theories including second order mechanism (such as Two Step 2, TS2) are generally in better agreement with the experimental data than these only including first order mechanisms (such as Shake Off and Two Step 1). This demonstrates that under present kinematics, second order mechanism plays an important role or even dominates over first order mechanisms. Besides, all DI results are compared with the predictions of TS2 kinematical analysis developed by Lahmam-Bennani et al (2010). Most of the structures shown in the measured angular distribution can be correctly explained by the TS2 kinematical analysis predictions. Besides, we extend this model by including the recoil contribution in each step. Some structures which cannot be explained by the previous model are well explained by the extended TS2 kinematical model. The isoelectronic target structure influence in DI is investigated preliminarily. The (e, 3-1e) results on Ne and CH₄ indicate the differences under same kinematics. The data analysis is underway.