No description available.

No description available.

This work examines the isotopic composition and abundance of helium in a number of different crustal environments with a view to understanding its production and transport in the crust. The work was largely carried out using existing instrumentation, but a dedicated interface was also built to allow computer control of a quadrupole mass spectrometer for rare gas abundance pattern determination. Conventional calculations of the radiogenic <SUP>3</SUP>He/<SUP>4</SUP>He production ratio based on the assumption of a chemically homogeneous composition cannot adequately account for the <SUP>3</SUP>He/<SUP>4</SUP>He ratio in waters from the Carnmenellis Granite of SW England. Alpha tracking and back-scattered electron microscopy show that the majority of the U and Th are concentrated in volumetrically insignificant accessory minerals. A new model has been devised, taking this heterogeneity into account, to explain the Carnmenellis data. Helium isotopic analysis of the granite itself revealed isotopic disequilibrium with the circulating waters. This may be related to differential release of <SUP>3</SUP>He and <SUP>4</SUP>He associated with different formation sites. A survey was made of the helium abundance and isotopic composition of groundwaters from the Pannonian Basin of Hungary in order to study the behaviour of mantle-derived fluids in an area of major recent crustal extension and volcanism. More than 80 samples were analysed covering most of the basin, and almost all contained a component of mantle-derived helium. Although <SUP>3</SUP>He/<SUP>4</SUP>He ratio is not clearly correlated with the surface expression of volcanism, it may act as an indicator of intrusion at depth. The <SUP>3</SUP>He flux through the Hungarian crust is ≈4 atoms.cm<SUP>-2</SUP>.s<SUP>-2</SUP>. If the mechanism of extraction is partial melting, then by analogy with melt production at mid-ocean ridges, addition of a 20-40 metre layer of basalt (for 5-10% partial melting) must be added to the Hungarian crust in a million years to support the present day <SUP>3</SUP>He flux.

No description available.

No description available.

Clusters of atoms have remarkable optical properties that were exploited since the antiquity. It was only during the late 20th century though that their production was better controlled and opened the door to a better understanding of matter. Lasers are the tool of choice to study these nanoscopic objects so scientists have been blowing clusters with high intensities and short duration laser pulses to gain insights on the dynamics at the nanoscale. Clusters of atoms are an excellent first step in the study of bio-molecules imaging. New advancements in laser technology in the shape of Free Electron Lasers (FEL) made shorter and shorter wavelengths accessible from the infrared (IR) to the vacuum and extreme ultra-violet (VUV and XUV) to even X-rays. Experiments in these short wavelengths regimes revealed surprisingly high energy absorption that are yet to be fully explained. This thesis tries to increase the global knowledge of clusters of rare-gas atoms interacting with short duration and high intensity lasers in the VUV and XUV regime. Theoretical and numerical tools were developed and a novel model of energy transfer based on excited states will be presented. The first part describes the current knowledge of laser-cluster interaction in the short wavelength regime followed by the description of the new model. In the second part of the thesis the different tools and implementations used throughout this work are presented. Third, a series of journal articles (of which four are published and one to be submitted) are included where our models and tools were successfully used to explain experimental results.

The vibrational energy levels of various rare gas trimers, Ar(_3), Ne(_3), He(_3), Ar(_2)Ne and Ne(_2)Ar, have been calculated using a coupled channel approach. We have compared results obtained with previous calculations. The existence of Efi-mov states in He(_3) has been investigated, and no evidence of their existence has been found. The affect of the Eckart conditions on embedding axis into a rotating-vibrating system has been investigated for several rare gas systems. A wide range of rare gas trimers have been studied, Ar(_3), He(_2)Ar, Ar(_2)He, Ar(_2)Ne and Ne(_2)Ar. For each trimer the full range of molecular motion is investigated. The low energy minima for the Ar(_n)N(_2) and Ne(_n)N(_2) systems have been found using simulated annealing search, and a gradient based minimisation technique, of a pairwise potential energy surface. Clusters with n ≥ 12 have been studied, and first solvation shells for both systems have been proposed. For each value of n, for n = 1 - 12, the first few low energy minima of the potential energy surface have been found. From these studies, we have gained a detailed understanding of the interplay of forces that determine the low energy structures for these systems. The affect of three-body interactions on the low energy minima both rare gas-N(_2) systems has been studied. In both system, rare gas-rare gas and rare gas- threebody interactions have been taken into account. This study has shown that the three-body forces have a small affect on the low energy structures of each system.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: G. J. Schrobilgen. Includes bibliographical references (leaves 305-318).

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: G. J. Schrobilgen. Includes bibliographical references (leaves 305-318).

Clusters of atoms have remarkable optical properties that were exploited since the antiquity. It was only during the late 20th century though that their production was better controlled and opened the door to a better understanding of matter. Lasers are the tool of choice to study these nanoscopic objects so scientists have been blowing clusters with high intensities and short duration laser pulses to gain insights on the dynamics at the nanoscale. Clusters of atoms are an excellent first step in the study of bio-molecules imaging. New advancements in laser technology in the shape of Free Electron Lasers (FEL) made shorter and shorter wavelengths accessible from the infrared (IR) to the vacuum and extreme ultra-violet (VUV and XUV) to even X-rays. Experiments in these short wavelengths regimes revealed surprisingly high energy absorption that are yet to be fully explained. This thesis tries to increase the global knowledge of clusters of rare-gas atoms interacting with short duration and high intensity lasers in the VUV and XUV regime. Theoretical and numerical tools were developed and a novel model of energy transfer based on excited states will be presented. The first part describes the current knowledge of laser-cluster interaction in the short wavelength regime followed by the description of the new model. In the second part of the thesis the different tools and implementations used throughout this work are presented. Third, a series of journal articles (of which four are published and one to be submitted) are included where our models and tools were successfully used to explain experimental results.