Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Physics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / Ph.D.

Measurements of the target thickness dependence of the target x-ray production yield for incident fast heavy ions are reported for thin solid Cu targets as a function of both incident projectile atomic number and energy. The incident ions were F, Al, Si, S, and CI. The charge state of the incident ions was varied in each case to study the target x-ray production for projectiles which had an initial charge state, q, of q = Z₁, q = Z₁ - 1, and q < Z₁ - 1 for F, Al, Si, and S ions and q = Z₁ - 1 and q < Z₁ - 1 for C1 ions. The target thicknesses ranged from 2 to 183 ug/cm². In each case the Cu K x-ray yield exhibits a complex exponential dependence on target thickness. A two-component model which includes contributions to the target x-ray production due to ions with 0 and 1 K vacancies and a three-component model which includes contributions due to ions with 0, 1, and 2 K vacancies are developed to describe the observed target K x-ray yields. The two-component model for the C1 data and the three-component model for the F, Al, Si, S, and C1 data are fit to the individual data for each projectile, and the cross sections for both the target and projectile are determined. The fits to the target x-ray data give a systematic representation of the processes involved in x-ray production for fast heavy ions incident on thin solid targets.

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Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The aim of this work was to study the 208Pb(p,2p)207Tl quasi-free knockout process. The experimental data were measured at the National Accelerator Centre using incident polarised protons of 200 MeV. The two scattered particles, from the knockout reaction, were detected in coincidence and their energies were determined using a magnetic spectrometer and a solid state detector telescope. Cross section and analysing power energy distributions were extracted from the experimental measurements and these were compared with theoretical values for the Distorted Wave Impulse Approximation. The theoretical cross-section calculations predict the experimental cross-section distribution well for all combinations of distorting potentials and bound states that were investigated, both with regard to shape, as well as absolute magnitude. However the theoretical analysing power distributions did not agree with the experimental quantities. Therefore it is not clear whether the analysing power is a useful tool to extract information on the specifics of the quasi-free reaction mechanism. The spectroscopic factors were found to be consistent with the results obtained in previous studies, thereby inspiring confidence that the problem with the analysing power distribution is not ascribable to a possible deficiency in the experimental techniques exploited in this work. / AFRIKAANSE OPSOMMING: Die doel van die studie was om die kwasi vrye 208pb(p,2p )207TI verstrooingsproses te ondersoek. Die eksperimentele data is ingewin by die Nasionale Versnellingsentrum deur gebruik te maak van 'n 200 MeV gepolariseerde proton bundel. Die twee verstrooide deeltjies is in koïnsidens gemeet. Vir die metings is 'n magnetiese spektrometer en 'n vastetoestand detektorteleskoop gebruik. Die kansvlak- en analiseervermoë-energieverdelings is uit die eksperimentele data verkry en is vergelyk met die berekenings van die Vervormde Golf Impuls Benadering. Die teoretiese kansvlak berekening het die eksperimetele data goed voorspel, vir die verskillende parametrisering van potensiaal en gebonde toestande. Die berekeninge het goed ooreengestem met betrekking tot beide vorm en absolute grootheid. Die berekende analiseervermoë het egter nie goed met die eksperimentele data ooreengestem nie. Dit is dus nie duidelik of die analiseervermoë 'n handige instrument is om inligting oor die betrokke kwasi-vrye reaksie meganisme te bekom nie. Die spektroskopiese faktore was in ooreenstemming met resultate wat in vorige studies verkry is. Dit versterk vertroue dat die probleem met die analiseervermoë nie toegeskryf kan word aan die eksperimentele tegniek wat gebruik is nie.

Measurements of the differential cross sections for backward (pi)('+)p and (pi)('-)p elastic scattering have been made for incident pion momenta between 30 and 90 GeV/c in the angular range 0 ) p(pi)('-), the (DELTA)(,(delta)) and N(,(alpha)) for (pi)('+)p (--->) p(pi)('+). As is given by this model, the momentum dependence of the differential cross-section, d(sigma)/du for fixed u, may be parameterized with the form (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) The values n('+) = 2.31 (+OR-) 0.07 and n('-) = 2.08 (+OR-) 0.06 are obtained for n at u = 0 for (pi)('+) and (pi)('-) scattering respectively.

Measurements of the differential cross-section for elastic scattering of positive and negative kaons off of a proton target are given in this dissertation. The beam momenta were 100 GeV/c and 200 GeV/c. The range of t, the four momentum transfer squared, measured was 0.4 < -t < 3.0. The experiment was performed at Fermilab. The data is consistent with previous experiments. Because of the much greater statistical accuracy of this experiment, it is now clear that the apparent equality of the pion and kaon cross-sections at larger t was due to poor statistical accuracy. The experimental results are not predicted by any theory. Furthermore, the difference between the pion and kaon differential cross-sections is not explained by geometrical scaling, as it was in the past.

The objective of this thesis is to describe the development, construction and use of a new tool for optical coherent transient spectroscopy. The new tool is a frequency-switched CO₂ laser. A highly stable laser design was modified to include an intra cavity electro-optic modulator, which al lows the output of the laser to be frequency-switched. The frequency modulated output is used in spectroscopic experiments whose goals are the determination of decay rates for infrared moIecuIar transitions. The use of a frequency-switched laser is the most prom i sing means of making such measurements on nonpoIar molecules. The use of an electro-optic crystal inside a laser cavity introduces a number of fundamental problems which must be overcome before the instrument can be used to make useful spectroscopic measurements. These problems are brought about by the need for a stable laser amplitude and frequency output. The development of a novel stabilization technique to overcome these problems is documented in this thesis. Also included in this thesis is a description of the microcomputer and associated electronics necessary to integrate the laser into an experimental apparatus capable of performing signal averaging and background subtraction on raw time resolved data. The final chapters of this work describe experiments and results of measurements of the scattering cross sect ions of a nonpolar molecule with rare gas perturbers. The nonpolar molecule is SF₆ and the rare gas collision partners are Helium, Argon, and Xenon. The results indicate that the scattering cross section for state changing collisions displays a mass dependance predicted by classical collision theory. However, the measured cross sections for elastic velocity-changing collisions appears to be mass independent, which is at variance with theory.

The K-shell x-ray and ionization cross sections are measured for protons on Ag, Cd, Sn, Sb, Te, Ba, and La over the ion energy range of 0.6 to 2.0 MeV. The data are compared to the predictions of the PWBA, the PWBA with corrections for binding energy and/or Coulomb deflection, the BEA, and the constrained BEA predictions. In general, the non-relativistic PWBA with binding energy correction gives the best overall agreement with the measurements of proton-induced x-ray processes for the K-shell of the elements studied in this work. The data further suggest the need for relativistic PWBA treatment of the interactions in the K-shell for the range of binding energies represented by the elements investigated in this work.

K-Shell ionization cross section for protons over the energy range of 0.4 to 2.0 MeV have been measured on thin targets of the elements Se, Br, Rb, Sr, Y, Mo and Pd. Total x-ray and ionization cross sections for the K-shell are reported. The experimental values of the ionization cross sections are compared to the non-relativistic plane-wave Born approximation, the binary-encounter approximation, the constrained binary-encounter approximation, and the plane-wave Born approximation with corrections for Coulomb-deflection and binding energy effects.

Experimentally measured L-shell x-ray production cross sections are presented for 8-36-MeV oxygen-ion bombardment of Ce, Pr, Sm, Eu, Dy, and Ho; for 4-32-MeV carbon-ion bombardment of La and Yb; for 6-32-MeV carbon-ion bombardment of Pr, Nd, Sm, and Dy; and for ll-29-MeV carbon-ion bombardment of Ce, Eu, Gd, and Ho. Theoretical predictions via the plane wave Born approximation (PWBA) with corrections for increased binding of target electrons and Coulomb deflection of the incident projectile tend to underestimate the experimental data; and this underestimation tends to get worse at the low- and high-energy ends of the range of energies used in this work.