Transmutation of plutonium and minor actinides in accelerator-driven systems (ADS) is being envisaged for the purpose of reducing the long-term radiotoxic inventory of spent nuclear reactor fuel. For this reason, the physics of sub-critical systems are being studied in several different experimental programs across the world. Three of these experiments have been studied within the scope of the present thesis; the MUSE experiments in France, the Yalina experiments in Belarus and the SAD experiments in Russia. The investigations of the MUSE experiments have focused on three different neutronic parameters; the neutron energy spectrum, the external neutron source efficiency and the dynamic neutron source response. It has been shown that the choice of external neutron source has negligible effect on the neutron energy spectrum in the core. Therefore, from this point of view, the MUSE experiments can be considered representative of an ADS. From the analyses of different reactivity determination methods in the Yalina experiments, it can be concluded that the slope fit method gives results in good agreement with the results obtained by the Monte Carlo method MCNP. Moreover, it was found that the Sjöstrand method underestimates keff slightly, in comparison with MCNP and the other investigated methods. In the radiation shielding studies of the SAD experiments, it was shown that the entire part of the effective dose detected at the top of the biological shielding originates from the proton-induced spallation reactions in the target. Thus, it can be concluded that the effective dose is directly proportional to the proton beam power, but independent of the reactivity of the sub-critical core. In order to study the energy gain of an ADS, i.e., the core power divided by the proton beam power, the proton source efficiency, ψ*, has been studied for various ADS models. ψ* is defined in analogy with the neutron source efficiency, φ*, but relates the core power directly to the source protons instead of to the source neutrons. φ* is commonly used in the physics of sub-critical systems, driven by any external neutron source (spallation source, (D,D), (D,T), 252Cf spontaneous fission etc.). On the contrary, ψ* has been defined only for ADS studies, where the system is driven by a proton-induced spallation source. The main advantages of using ψ* instead of φ* are that the way of defining the external source is unique and that ψ* is proportional to the energy gain. An important part of this thesis has been devoted to studies of ψ* as a function of different system parameters, thereby providing a basis for an ADS design with optimal properties for obtaining a high core power over beam power ratio. For instance, ψ* was found to decrease considerably with increasing spallation target radius. / QC 20101005

This thesis presents measurements of fundamental properties of singly charged ionic systems including spectral wavelengths, lifetimes of excited states and branching fractions with the main focus on time resolved laser spectroscopy of stored ions providing lifetime measurements of metastable states. The results of these measurements have been used to determine energy levels and transition probabilities of the studied systems. The included experimental data are compared with results from calculations which provides evaluations of different theoretical models. The presented results have been applied by others to the field of atomic astrophysics in order to deduce electron densities and elemental abundances in ejecta of the supermassive star eta Carinae and have also been followed by additional work of theoreticians interested in comparisons with laboratory data. The thesis is a result of several collaborations in which Stockholm University has been providing lifetime measurements of metastable states, Lund Observatory and the National Institute of Standards and Technology have been providing wavelength and branching fraction measurements, Lund Laser Centre has been providing lifetime measurements of short-lived states and calculations have been performed by theoretical physicists from Université de Mons-Hainaut, Université de Liège, Queen's University of Belfast and Laboratoire Aimé Cotton.

The experimental success in ultra-cold atomic gases, both bosonic and fermionic have boosted the theoretical studies, and especially the a lot of numerical techniques have been developed and used to describe them. In this thesis, we introduce two numerical experiments in our group on ultra-cold atomic gases. The first concerns the scalar dipolar condensate. We have developed and implemented a Split-Step Fourier scheme in imaginary time, which enable us to seek the ground state of the dipolar condensate. The second part is focused on our ongoing efforts to investigate the trapped spin polarized Fermi gas using self-consistent Bogoliubov-de Gennes (BdG) calculation.

The formation of K+···Cl- heavy-Rydberg ion-pair states through dissociative electron attachment in K(np)/CCl4 collisions is investigated. The product ion-pair states are detected directly by electric field-induced dissociation. A Monte Carlo collision code is used to analyze the results that models both the initial Rydberg electron attachment and the subsequent evolution of the ion pairs. The data and the calculations demonstrate the production of long-lived bound K+···Cl- heavy-Rydberg ion pairs. They also suggest that collinear collisions can generate heavy-Rydberg states of low angular momentum.

The formation of heavy Rydberg ion-pair states through electron transfer in collisions between K(np) Rydberg atoms and molecules that attach low-energy electrons is investigated. At low n, collisions with a wide variety of target species can lead to the formation of hound ion-pair states, a small fraction of which (under apropriate conditions) can subsequently dissociate as free ions through internal-to-translational energy transfer. The lifetimes of the ion-pair states can also be influenced by autodetachment of the electron or by neutralization through charge transfer. Two primary methods are employed to investigate the lifetimes of ion-pair states. Measurements of the onsets in the arrival time distribution of the ions provide lifetime information on short time scales (a few microseconds or less) for those ion pairs which undergo dissociation through conversion of internal energy. Additionally, ion pair behavior on longer time scales (> 1 --- 2 micros) can be studied as a function of binding energy through direct field dissociation.

Tropolone (TRN), a pseudo-aromatic molecule which undergoes intramolecular proton transfer in both its ground and excited states, has been chosen as a model for the study of excited state proton transfer processes in polyatomic molecules. TRN is an excellent model for studying the mechanism and dynamics of intramolecular excited state proton transfer because of its simple chemical structure, photochemical stability, and readily observable tunneling doublet splittings whose magnitudes are dependent on isotopic substitution, vibrational excitation, and solvation. The spectroscopy and photophysics of TRN in the vapour phase, in a variety of solvents, and in microscopic van der Waals solvent clusters have been investigated. Energy and time resolved spectroscopic techniques have been used to study the first excited singlet state of TRN in a supersonic jet expansion. The lifetime of TRN excited to the origin of the S1 1([pi],[pi]*) state is 1.17 ns and decreases rapidly with excess vibrational energy in the excited state. The data are interpreted in terms of an increased non-radiative decay rate which is a result of perturbations in the S1 potential energy surface resulting from enhanced vibronic coupling to a nearby 1(n,[pi]*) state. The absorption, emission, and excitation spectra of TRN have been recorded in a variety of polar, non-polar, and hydrogen bonding solvents and the fluorescence quantum yields have been determined. In perfluoro-n-hexane and in aqueous solution the lowest energy singlet state is of ([pi],[pi]*) character. In n-hexane, carbon tetrachloride, acetonitrile and methanol solutions it is postulated that an inversion of the two lowest excited singlet states of TRN occurs and that the lowest energy singlet state is of (n,[pi]*) character. The structures and excited state proton transfer properties of the vdW complexes of TRN with CO, n-alkanes, perfluoro-n-alkanes, CFH3, CF2H2, CF3H, and CO2 have been investigated using LIFE spectroscopy and empirical Lennard-Jones and ab initio theoretical methods. The solvent molecules are found to bind to TRN either by primarily dispersive intermolecular forces above the plane of the seven-membered ring, or by hydrogen bonding to the hydroxyl and keto moieties of the chromophore.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 115-131). Available also in a digital version from Dissertation Abstracts.

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M. Tech. Chemistry / Recently, traditional electro-thermal atomic absorption spectrometry has lost its popularity to other multi-element spectrometric techniques. Limited linear determination range, which is usually two orders of magnitude, is one of the reasons for the loss. As a result, tens of calibration standards and diluted samples have become an indispensable part of the electro-thermal atomic absorption spectrometric analysis, particularly if numerous samples containing a broad concentration range of analytes are to be analysed. The objective of this work was to establish the mechanism of absorption signals for high concentrations of analyte atoms in the absorption volume. Secondly, to employ the findings for HR-CS ET-AAS data quantification, within a broad range of analyte concentrations. It was expected that the sought algorithm would permit the use of the most sensitive analytical lines or those less prone to interferences, independent of the concentration of the respective analyte in the sample.

UV spectrometry (187–380 nm) with charge coupled device (CCD) detection was used to study the evolution of absorption spectra during the vaporization of various species in the pyrocoated graphite furnace, with electrodeposited Ir and Rh as modifiers. In order to mimic a typical matrix composition, various salts of aluminum, manganese, copper, magnesium, sodium, and lead were used in microgram amounts. Changes in spectra and vapor release rate, along with aging of the tubes in the repetitive temperature cycles, were observed. Compared to the unmodified pyrocoated tubes, the presence of Ir or Rh causes a significant reduction in the vaporization efficiency, especially for microgram amounts of copper and aluminum introduced as nitrates, and manganese introduced as a sulfate. The vaporization efficiency, for magnesium and sodium as chlorides, and for lead as a sulfate, remained unchanged. Interestingly, the aging of the tubes was accompanied by partial restoration of the spectral characteristics for unmodified tubes. For example, with unmodified pyrocoated tubes, the vaporization spectrum, appearing as a consequence of the decomposition of aluminum nitrate, consisted of Al2O bands overlapped by Al atomic lines. In the freshly modified tubes, intensities of those lines and bands were substantially reduced, and in this case, the dominance of AlO molecules was observed. The efficiency of vaporization of aluminum species increased in the aged modified tubes. The scanning electron microscopy (SEM) images of the modified surfaces for the new and aged tubes indicated that aging of the tubes is accompanied by the destruction of the pyrocoating, formation of pyrographite shells around the areas where the modifier was electrodeposited, and finally, complete substitution of the metal on the graphite surface by pyrographite debris.