Zugl.: Berlin, Freie Univ., Diss., 2008

Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 4, 2009) Includes bibliographical references (p. 78-82).

Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Includes bibliographical references (leaves 97-107).

Thesis (M.S.)--Massachusetts Institute of Technology, 1968. / Includes bibliographical references (leaves 57-58).

Marburg, University, Diss., 2002.

In the work described in this thesis attempts have been made to obtain information on three aspects of the behaviour of liquid argon as an ionization counter. Ionization was produced by alpha particles from a source deposited on the negative electrode of a small parallel-plate chamber in which pure argon was liquefied. The current pulses resulting from movement of the liberated electrons in the field applied to the plates were analysed electronically. Firstly, it was desired to determine the time taken by the electrons originating from distinct ionization events to traverse measured electrode separations and be collected by the positive electrode. These transit times depend upon the electron mobility in liquid argon, defined as the velocity of the electrons per unit field. From this mobility, the mean free path and collision cross-section of the electrons with respect to argon atoms can be calculated. Some estimates of transit times and mobilities, and resulting values of mean free path and cross-section are given. However, it appears that limitations of the electrode spacing and the applied field cause the transit time to be so short as to necessitate the use of wide band amplifiers with, consequently, high noise levels. Secondly, the causes of variation in size of current pulses with angle of emission of the initiating alpha particles were investigated. The effect of greatest interest was that, due to the geometry of the chamber, as from it a determination was made of the range of alpha particles in liquid argon. For 5.3 MeV alpha particles, the weighted centre of ionization was found to be 0.006 cms. from the source, implying a particle range of about 0.009 cms. The number of electrons contributing to current pulses was also found to be a function of the angle of emission, on account of a variable degree of recombination with the positive ion column. This number was determined, and even under the most advantageous conditions fell considerably short of the probable total number liberated. This fact imposes a serious limitation on the potentialities of liquid argon as a useful counter. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The objectives of this work are twofold: firstly, to understand the inductively coupled argon plasma (icp) from a fundamental point of view and, secondly, to attempt to put that knowledge to practical use. In an effort to realize this first objective, a simple two-level rate model was developed which allows the estimation of the deviations (due to radiative decay) of analyte level populations in the icp from local thermodynamic equilibrium (lte). The results were found to agree very well with experiment for analyte elements (Fe, Cr and Ba) which did not exhibit charge transfer with the argon support gas. A comprehensive study of magnesium excited-state level populations was performed. It was found that charge transfer between argon ions and ground state magnesium atoms caused ionic magnesium to be overpopulated (with respect to the simple rate model calculations mentioned above). It was also found that, due to appreciable self-absorption, argon itself conforms to an lte model. Electron temperatures (Te) were measured in the icp. It was found that, for electron densities greater than about 2x10¹⁵ cm⁻³, Te was within experimental uncertainty of the so-called lte temperature (Te,lte - calculated from the electron density). At lower electron densities, due to the large experimental errors involved, it was difficult to draw definitive conclusions regarding their agreement. The plasma was also extensively characterized when an extra argon flow was added to the aerosol gas. It was found that at low values of the aerosol gas flow rate, mixing between it and the plasma gas was relatively complete, whereas at higher flow rates there was relatively little mixing. It was also found that the introduction of water into the plasma had a limited effect on sample excitation. In order to fulfil the second objective, a method was developed to simulate emission spectra from an icp. The method involved the use of a computer program, which worked by combining basic physical data for atomic species, the results of icp fundamental studies, and a realistic instrumental line profile (described in detail). The method was used to simulate a hypothetical silver determination in NBS coal fly ash showing the effects of spectrometer bandpass, silver concentration, and line choice on spectral overlaps. / Science, Faculty of / Chemistry, Department of / Graduate

The absolute transition probabilities between the 3p⁵4s and 3p⁵4p configurations of neutral argon have been measured in a three part experiment. In the first experiment, a technique of absorption spectroscopy was used to obtain relative transition probabilities for spectral lines with a common lower level. Secondly, relative transition probabilities were obtained for spectral lines with a common upper level by measuring the relative intensities of suitable pairs of lines in an emission experiment. In the third experiment, the relative values were converted to absolute transition probabilities by obtaining the lifetime of the P₁-S2 transition at ʎ7503Å. The experimental techniques used in this experiment were developed by Robinson (1966) and van Andel (1966). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The purposes of this thesis are to examine ages of the Nelson batholith and its satellites because of the wide range of biotite model ages previously published in the literature, and to test hornblende and pyroxene further for their application in K⁴⁰ - Ar⁴⁰ dating as reliable minerals. K⁴⁰ - Ar⁴⁰ model ages obtained on biotite, hornblende and clinopyroxene from the present study indicate with certainty that the various phases of the Nelson batholith were emplaced during a short span of time, centered around 156 m.y. corresponding to the Upper-Middle Jurassic boundary of the Kulp’s time scale. At least a period of hydrothermal alteration has occurred in this area since that time. It is evident that these phases cannot be distinguished on the basis of their K⁴⁰ - Ar⁴⁰ model ages. It is also evident that hornblende gives reliable model ages. Clinopyroxene contains significant excess of radiogenic argon and should not be used for K⁴⁰ - Ar⁴⁰ dating. Biotite may occasionally contain excess of radiogenic argon, particularly under high temperature and high argon pressure environmental conditions. Analytical techniques used and descriptions of the samples analyzed are given as appendixes. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The angle, distance and vibration dependence of the Ar-CO intermolecular potential is calculated using the electron gas model to obtain the short range interaction which is smoothly joined onto the long range van der Waals tail which is obtained from accurate C_6, C_7, and C_8 coefficients. Our calculated second interaction virial coefficients are compared with experiment and with a simple adjustment of the Ar-CO potential an excellent agreement is obtained. Our spherically averaged potential is also in excellent agreement with a spherical potential inferred from high energy scattering data. Simplified expressions for the scattering amplitude and differential cross section are obtained in the infinite order sudden approximation. Then, treating the rotations and vibrations in the infinite order sudden and close coupling approximations respectively, vibrational transition probabilities and relaxation rates are calculated using the Ar-CO intermolecular potential. Our calculated vibrational relaxation rates are much smaller than the experimental values.