The polarized and unpolarized differential cross-sections and the analyzing power angular distributions of the pp→π⁺ d reaction have been measured to a statistical precision of better than one percent over several incident proton beam energies between 350 and 500 MeV for center-of-mass angles from 20° to 150°. The unpolarized differential cross-sections were measured at 350, 375, 425, and 475 MeV with unpolarized incident beams. The polarized differential cross-sections and analyzing powers were measured at 375, 450, and 498 MeV using polarized incident beams. Angular distributions of the unpolarized and polarized differential cross-sections are expanded into Legendre and Associated Legendre polynomial series respectively, and the ai°° and biⁿ° expansion coefficients fit to the respective measurements. The resulting coefficients are compared with existing data and recent theoretical predictions. The observation of significant non-zero a₆°° coefficent is interpreted as indication of a significant contribution from the ¹G₄ N-N partial wave channel at energies as low as 498 MeV. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Electron momentum spectroscopy (EMS) provides experimental atomic and molecular electronic structure information in terms of the binding energy spectrum and the experimental momentum profile (XMP), which is a direct probe of the electron momentum distribution in specific molecular orbitals. The measured XMPs permit a detailed quantitative evaluation of theoretical ab initio wavefunctions in quantum chemistry and also provide a means to investigate traditional concepts in chemical reactivity at the fundamental electronic level. This thesis reports high momentum resolution EMS measurements of the valence orbitals of H₂0, D₂0, NH₃ and H₂CO obtained using an EMS spectrometer of the symmetric, non-coplanar type operated at an impact energy of 1200eV. The measured experimental momentum profiles for the valence orbitals of each molecule have been placed on a common intensity scale, which has allowed a stringent quantitative comparison between experiment and theory. These studies now confirm earlier preliminary investigations that suggested serious discrepancies between experimental and theoretical momentum distributions. Exhaustive consideration of possible rationalizations of these discrepancies indicate that double zeta quality and even near Hartree-Fock quality wavefunctions are insufficient in describing the outermost valence orbitals of H₂0 and NH₃. Preliminary results for H₂CO also indicate that near Hartree-Fock wavefunctions are incapable of describing the outermost 2b₂ orbital. Interactive and collaborative theoretical efforts have therefore led to the development of new Hartree-Fock limit and also highly correlated (CI) wavefunctions for H₂0, NH₃ and H₂CO. It is found that highly extended basis sets including diffuse functions and the adequate inclusion of correlation and relaxation effects are necessary in the accurate prediction of experimental momentum profiles as measured by electron momentum spectroscopy. New EMS measurements are also reported for the outermost valence orbitals of NF₃, NH₂CH₃, NH (CH₃)₂, N (CH₃)₃ and para-dichlorobenzene. These exploratory studies have illustrated useful chemical applications of EMS. In particular, EMS measurements of the outermost orbitals of the methylated amines have revealed chemical trends which are consistent with molecular orbital calculations. These calculations suggest extensive electron density derealization of the so-called nitrogen 'lone pair' in the methylated amines in comparison to the 'lone pair' in NH₃. EMS measurements of the non-degenerate π₃ and π₂ orbitals of para-dichlorobenzene show different experimental momentum profiles consistent with arguments based on inductive and resonance effects. These experimental trends, both in the case of the amines and para-dichlorobenzene, were qualitatively predicted by molecular orbital calculations using double zeta quality wavefunctions. However more accurate prediction of the experimental momentum profiles of these molecules will need more extended basis sets and the inclusion of correlation and relaxation effects as suggested by the studies based on the smaller molecules. An integrated computer package (HEMS) for momentum space calculations has also been developed based on improvements to existing programs. Development studies testing a new prototype multichannel (in the ɸ plane) EMS spectrometer are described. / Science, Faculty of / Chemistry, Department of / Graduate

Electron impact ionization is an important phenomenon touching many areas of science, and much research has been done over the years on various aspects of this process. Efforts to establish the precise variation of ionization cross section with energy were initiated in the early 1950's; however, severe disagreements between experimental data concerning fine structure observed in the electron impact ionization efficiency curves were reported from laboratory to laboratory. The work in this thesis has been largely devoted to establishing the credibility of the method of electron impact ionization by monoenergetic electron beam in the study of such fine structure. The design and construction of an apparatus to study the ionization of atoms and molecules by an electron beam of narrow energy width are described, and preliminary data on krypton and argon near the ionization threshold energies discussed. A sound basis has been laid for further development in this field. / Science, Faculty of / Chemistry, Department of / Graduate

Evaluation of several methods of fixing chicken skin for scanning electron microscopy (SEM) indicated standard chemical fixation using glutaraldehyde and osmium tetroxide followed by chemical dehydration with 2,2-dimethoxypropane to be the method of choice. SEM revealed that chicken skin has a convoluted surface. Two types of chicken skin, distinguishable on the basis of chemical composition and appearance were observed. Type I has a filamentous surface with 55% moisture and 25% fat, whereas Type II skin has a globular appearance, 52% fat and 33% moisture. The fatty acid profiles of Types I and II skin are the same. Bacteria have greater affinity for Type II than Type I skin. Attachment studies indicated that Salmonella typhimurium quickly attach to the skin surface and cannot be removed easily by washing with water or with water containing a surfactant. / Land and Food Systems, Faculty of / Graduate

Electron Nuclear Double Resonance (ENDOR) measurements have been made of hyperfine couplings in x-irradiated single crystals of sodium formate and potassium hydrogen bisphenylacetate (KHBP). In sodium formate ENDOR signals were obtained from both proton and sodium ion neighbours of the CO^" centre formed on irradiation. ENDOR studies 23 of the Na hyperfine interaction together with CNDO calculations indicate that the CO^" forms a tight ion pair with the nearer Na+ cation, thus explaining the four line EPR hfs. observed. Hf. interactions have also been resolved for four pairs of nearest neighbour protons. The tensors are mainly dipolar in character, but contain some isotropic contributions which are interpreted in terms of covalent interactions. 23 Extra so-called 'forbidden' lines are observed in the Na ENDOR and a model of ENDOR enhancements involving cross relaxation with other paramagneti species is suggested. (#2" was also observed in uv-irradiated samples: the threshold energy for radical formation was estimated to be 100+10 kcal mole A previously reported free-radical reaction in sodium formate was found to be reversed by uv irradiation, the reaction obeying second order kinetics. Proton ENDOR studies of x-irradiated KHBP confirmed the presence of the benzyl radical, for which all seven anisotropic proton hyperfine tensors were measured. The isotropic couplings agree with earlier EPR measurements of the benzyl radical undergoing free rotation. The dipolar couplings provide an independent estimate of the spin density distribution in the radical which is not in complete accord with earlier determinations based on the McConnell relation. The dipolar tensors imply a spin distribution close to that predicted by INDO and other calculations, which suggests that these calculations may be qualitatively correct, and the McConnell relation not strictly applicable. Several other radicals are also present in irradiated KHBP. Two are tentatively identified as cyclohexadienyl type radicals formed by hydrogen addition at the phenyl ring ortho and para to the methylene carboxy group. / Science, Faculty of / Chemistry, Department of / Graduate

<p>In this work, we investigate the electron transparency of graphene structure using well-established experimental techniques. We further compare the results to numerically obtained values and find excellent agreement between the two. We further analyze the dependency of graphene electron transparency on several physical parameters of the setup, including the width of the incident electron Gaussian wave packet, emitter barrier height, applied bias voltage, and the collector work function. The results indicate that the low work function of doped graphene can enhance electron transmission for lower kinetic energies. The measurements and calculations demonstrate that graphene exhibits high electron transparency even at low electron kinetic energies, for example with transmission above 90% at 12 eV. As a consequence, graphene promises to be a potential candidate for electronic and biological device applications based on electron emission. </p>

Skin collimation in electron therapy ensures sharper penumbra and maximal protection to adjacent critical structures. It also provides a better clinical dose to the target and avoids recurrences at the periphery. The thickness of the electron skin collimation must be adequate for shielding purposes, not too thick to cause discomfort to the patient and be conformal to the skin. This study assessed the clinical potential of machined brass skin collimation with variable thickness. Brass transmission factors for 6, 9, and 12 MeV electron beams were measured and used to determine the skin collimation clinically acceptable thickness. Dosimetric performance of the variable thickness skin collimation was evaluated for 9 MeV electrons within a rectilinear water-equivalent phantom and a water-filled head phantom. Results showed the variable thickness skin collimation is dosimetrically equivalent to the uniform thickness collimation. Favorable dosimetric advantages for brass skin collimation for small electron fields were achieved. / Includes bibliography. / Thesis (PMS)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

This thesis is a study of the celestial gamma-ray flux. It reviews several of the proposed mechanisms for producing high energy gamma rays and describes several of the attempts to detect their presence. Also included is a short historical review of the spark chamber, along with a qualitative description of its operation.

We performed atomistic modeling to study structural and mechanical properties of materials. We used density functional theory (DFT) for all the studies presented and constructed a method for quickly optimizing semi-empirical modified embedded atom method (MEAM) potentials. In our first study, we show that the reconstruction model in the literature for GaSb(001) is not predicted to have the lowest surface reconstruction energy. A modification was proposed that improves the energy. The second study tries to validate a crystal structure for the Φ Phase of Al-Mg-Zn. The third study deals with plain carbon steel, including some microalloying of Vanadium and vacancy assisted diffusion of Fe in Cementite(Fe3C). In the fourth study, we show a method for optimizing a MEAM potential. The code written is specific to hexagonal closed packed structures and was applied to a Magnesium potential.

No description available.