Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies.

Thesis (M.A.)--University of Wisconsin--Madison, 1944. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Köln, Universiẗat, Diss., 2002.

Th. 3e cycle--Géochim.--Paris 7, 1983.

The energy distribution of charged photopartides from the interaction of the A⁴⁰ nucleus with 17.64 Mev and 14.7 Mev gamma rays from the reaction Li⁷ (p,ϒ)Be⁸ has been obtained using a gridded ionization chamber. A total cross section of 5.8 mb. was found for the combined production of photoprotons and photoalphas. Peaks in the energy spectrum corresponding to photoproton events leading to the ground and first excited states of the residua nucleus Cl³⁹ were identified but some features of the energy distribution remain unexplained. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Relative transition probabilities for some spectral lines connecting the 4s and 4p states of neutral argon have been determined by a relatively new technique developed by Seka and Curzon involving the Faraday effect. In this method a given spectral line emitted by an argon discharge tube is plane polarized and then passed through an absorption tube embedded in an axial magnetic field. The rotation of the plane of polarization, and the intensity of the source line are measured and from the results the absorption coefficient for that particular line in the plasma is deduced. The theory used agrees excellently with the observed rotations for field values from 0 to 2600 gauss. This technique is particularly suited to strong transitions which are difficult to measure by other methods. The values obtained here for the transition probabilities are quite accurate (errors < 10%) and agree well with values given by Weise in a recent compilation. For the analysis of the Faraday rotation it was necessary to determine the effect of the magnetic field on the number density of lower excited states in the absorbing plasma. This was done using a relative absorption technique, the results of which show a linear decrease in the number densities in the first 2000 gauss. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

La thématique abordée dans cette thèse relève de la manipulation d’un jet d’atomes d’argon métastables (Ar* ³P2) dans différentes configurations. Premièrement, je présente l’échange de métastabilité entre un atome au fondamental et un atome excité à de faibles énergies de centre de masse (entre 4 et 9 meV). Je propose également l’interprétation théorique par une approche semi-classique (approximation JWKB) qui se révèle validée, dans ce domaine d’énergies, en comparaison avec la résolution exacte de l’équation de Schrödinger radiale mettant en jeu les potentiels concernés par la collision. Les sections efficaces absolues d’échanges, déduites d’une analyse en temps de vol du signal métastable, permettent de réaliser une comparaison sans biais avec les prédictions théoriques. Les caractéristiques d’un jet ralenti par effet Zeeman sont dégradées par le processus de ralentissement et le rende difficilement utilisable en deçà de quelques dizaines de mètres par seconde. C’est pourquoi, dans un deuxième temps, je présente la réalisation d’un jet lent original, issu d’un piège magnéto-optique et présentant des caractéristiques remarquables. La vitesse est accordable entre 10 et 100 m/s, la dispersion de vitesse relative est très faible (6 % à 20 m/s) et le flux est conséquent (10⁹ Ar*/s/sr), pour une ouverture angulaire standard (35 mrad FWHM). Ce nouveau dispositif permet de présenter certaines questions d’interférométrie et d’optique atomique telles que les interactions atome-surface de type van der Waals et l’étude de potentiels comobiles ainsi que leurs applications dans la réalisation de milieux d’indice négatif ou de ralentisseurs. / The topic of this thesis concerns the manipulation of a metastable argon (Ar* ³p2) atomic beam in different configurations. Firstly, I present the metastability exchange between an atom in fundamental state and an excited atom at low center of mass energy (between 4 and 9 meV). I also propose theoretical interpretation by a semi-classical approach (JWKB approximation) which is validated, in this field of energies, compared to the exact solution of the Schrödinger radial equation with potentials involved in collision. The absolute exchange cross-sections, derived from a time of flight analysis of metastable signal, enable an unbiased comparison with theoretical predictions. The characteristics of a Zeeman slowedbeam are degraded by the process of slowing down and makes it difficult to use below a few tens of meters per second. Secondly, I present the realization of an original slow beam from a magneto-optical trap and having outstanding features. The atomic velocity is tunable between 10 and 100 m/s, the relative velocity dispersion is very low (6 % at 20 m/s) and the flow is substantial, (4.7×108 Ar*/s/sr), for a standard angular aperture (35 mrad FWHM). This new device can present some issues in atomic interferometry and atomic optics such as van der Waals atom-surface interactions or study co-moving potentials and their applications in negative-index media for matter wave or slowers.

No description available.

Thesis--Wisconsin. / Vita. Includes bibliographical references.

The annihilation of positrons in Argon has been investigated as a function of Argon density and applied electric field using the technique of lifetime measurements. Lifetime spectra were analyzed using the maximum likelihood method of curve fitting. Results obtained at zero electric field yielded a linear dependence on density for the direct annihilation rate of (5.6 ± 0.1) x 10⁶sec⁻1 amagat⁻¹, with some evidence of non-linearity at densities greater than 10 amagats. The density dependence of the long-lived component of the time spectra indicated a zero density intercept of (7.2 ± 0.4) x 10⁻⁶sec⁻¹ in agreement with the theoretical value of the free orthopositronium annihilation rate (7-2. x 10⁶ sec⁻¹ ). In addition an orthopositronium quenching rate of (0.29 ± 0.04) x 10⁶ sec⁻¹ amagat⁻¹ was obtained from the linear dependence of the orthopositronium annihilation rate on density. The electric field dependence of the direct annihilation rate and orthopositronium formation have been measured and are used to provide an internally consistent picture of the behaviour of positrons in a gas under the influence of an applied electric field. Furthermore, these results have been compared with theoretical results for the direct annihilation rate obtained from one parameter representations of the effective positron-Argon atom interaction. It is shown that, while such potentials are successful in describing the low-energy elastic-scattering of electrons from noble gas atoms, they are inadequate for the case of positrons. However, consideration of the way in which the direct annihilation rate changes as a function of electric field leads to an upper limit of 15π₀² for the momentum-transfer cross-section for positrons in Argon at thermal energies. Such an estimate is shown to be independent of any assumption concerning the effective positron-Argon atom interaction. / Science, Faculty of / Physics and Astronomy, Department of / Graduate