Ce manuscrit concerne l'analyse tectonique et géomorphologique du système de failles de Longriba (LFS), localisé à l'Est du plateau tibétain à environ 200 km au Nord-ouest de la chaîne des Longmen Shan. Le LFS est constitué de deux zones de failles décrochantes dextres, parallèles et d'orientation N55°E : la faille de Longriqu, au Nord, et la faille de Maoergai, au Sud. Le rôle géodynamique de ce système est primordial puisqu'il accommode 5 ± 1 mm/an de la composante décrochante induite par la convergence oblique du bloc Aba, elle-même liée à la collision Inde-Asie. De plus, le LFS partitionne la déformation de la marge Est tibétaine; les structures des Longmen Shan étant essentiellement chevauchantes. Cependant l'histoire long-terme du LFS est mal contrainte. L'objectif de cette thèse est donc d'apporter des informations spatio-temporelles sur l'activité du système à l'échelle du Cénozoïque. Pour cela trois études ont été réalisées. La première a permis de mieux contraindre le comportement sismogénique des deux zones de failles à l'aide d'images satellites de basse (90m) et très haute résolution (50cm). L'analyse des déplacements cumulés le long de la faille de Maoergai a permis de proposer que celle-ci était active vers ~15Ma. La seconde étude a mis en évidence un contrôle du système sur la répartition des taux de dénudation au travers de la marge Est tibétaine à l'échelle de l'Holocène. Enfin, les données de thermochronologie basse température suggèrent que la faille de Maoergai a accommodé un mouvement vertical vers ~10Ma. Ce mouvement est probablement lié au rebond isostatique de la marge, découplé du mouvement décrochant qu'elle accommode à la même période. / This manuscript concerns the tectonic and geomorphic analysis of the Longriba fault system (LFS), located in the eastern Tibetan plateau at about 200 km north-west of the Longmen Shan. The LFS consists of two dextral strike-slip fault zones, parallel and N55 °-trending: the Longriqu fault to the north and the Maoergai fault the south. The geodynamic role of the system is essential as accommodates 5 ± 1 mm / year of the slip component induced by the oblique convergence of the Aba block, itself linked to the India-Asia collision. In addition, the LFS partitions the deformation of the east Tibetan margin; the structures of the Longmen Shan are mainly thrust faults. However the long-term history of LFS is poorly constrained. The objective of this thesis is to bring spatial and temporal information on system activity throughout the Cenozoic. To do so, three studies were performed. The first led to better constrain the seismogenic behavior of the two fault zones with low resolution (90m) and very high resolution satellite images (50cm). The analysis of cumulative displacements along the Maoergai fault allowed to propose that it was active at ~ 15 Ma. The second study showed that the system controls the distribution of the denudation rates over the EastTibetan margin throughout the Holocene. Finally, the low-temperature thermochronology data suggest that, in particular, the Maoergai fault has accommodated a vertical movement at ~ 10 Ma. This movement is probably related to the isostatic rebound of the margin, decoupled from the strike-slip movement it accommodates at the same period.

<p> Part A Abstract </p> <p> Temperature coefficients of reactivity for an 37-element reference design of a thorium oxide fuelled, heavy water moderated and cooled reactor, are calculated. The physical processes which determine magnitude and sign of the coefficients are identified and discussed. Results are given for fresh fuel containing equilibrium concentrations of the fission product Xe-135 and with boron control in the moderator. Results are. also -given for fresh fuel with the equilibrium concentration of Xe-135 but without boron contorl for fuel with an exposue of 1.513 n/k barn and for fuel with an exposure of 3.13 n/k barn; each containing appropriate concentrations of 50 separate nuclides and one-pseudo fission product. The fuel temperature coefficient of reactivity is negative for all the cases studied, while the coolant temperature coefficient of reactivity is positive for all the cases studied. The void effect is an increase in reactivity for all cases studied. </p> ////////////////////// <p> Part B Abstract </p> <p> This work has been done with the purpose of studying the validity of Bragg Kleeman rule which states that for combinations of elements, the atomic stopping cross-sections are additive. The validity of Bragg Kleeman rule for low energy He ions has not been conclusively tested for solids. In this work, the comparison with the experimental stopping power of SiC with the additive stopping powers of Si and C has been made experimentally. </p> <p> A thick target technique in the experimental evaluation of the stopping powers is used. This method has some simplicity over the thin target techniques. </p> <p> A calibration of the McMaster University Van-de Graff accelerator was done. Experiments were conducted later using the calibration curves produced. </p> <p> The report contains a brief account on different sources of errors due to the Van-de-Graff accelerator calibration and due to stopping power experiments. </p> / Thesis / Doctor of Philosophy (PhD)