Thesis (Ph. D.)--University of Wisconsin--Madison, 1964. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 77-79).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

The differential cross section for direct radiative capture of protons by 0¹⁶ has been measured using ice targets of known thickness and 800 kev. protons. The differential cross section for the gamma ray transition to the first excited state in F¹⁷ was found to be (10.4 ± 1.3) x 10⁻⁻³² cm² per steradian at 90° to the incident proton beam direction. At the same energy, the ratio of the differential cross section at 90° for transitions to the ground state to that for transitions to the first excited state in F¹⁷ was found to be o.14 ± 0.03. The energy of the first excited state in F¹⁷ was determined by measuring the energy of the gamma ray from this level to the ground state. This method is difficult because of the presence of positron annihilation radiation of the same energy, within experimental errors, from the decay of F¹⁷. The first excited state energy was also measured by noting the difference between the capture gamma rays to this state and to the ground state. The energy of this level was found to be 0.50 ± 0.01 Mev. in agreement with the results of Marion and Bonner (55) and with earlier results obtained in this laboratory (Warren et. al., (54), An attempt to confirm that the source of the 873 kev. radiation from proton bombardment of natural oxide targets above 1.8 Mev. bombarding energy was the 0¹⁷(p, p',૪)0¹⁷ reaction, was made using separated 0¹⁶ and 0¹⁷ targets. The results were inconclusive due to the small percentage of oxygen that stuck to the targets and to the presence of several contaminants. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The efficiency of a 4" x 5" Nal(Tl) scintillation counter for detecting gamma-rays has been measured by a number of experimental techniques, and the results compared with the efficiencies predicted from total absorption cross sections. The experimental techniques involve coincidence measurements of the cascade gamma-rays from a Co-60 source (1.173 MeV and 1.333 MeV), and from the reaction B¹¹(pγγ)C¹² (4.43 MeV and 11.68 MeV). The Co-60 measurements also lead to knowledge of the absolute strength of the sources. For both cascades it was necessary to know the angular correlations between the radiations; for the reaction B¹¹ (pγγ)C¹² a separate investigation of this correlation was made using a 180 KeV accelerator. Computer programs were written to analyze the experimental data, and to calculate the theoretical efficiency estimates, taking into account the collimator and shield geometry. The results of this work define the efficiency of the scintillation counters to better than 5% for a number of gamma-ray energies and a specific geometry. On the other hand, the efficiencies based on the total number of counts in the observed spectra were 20 percent to 40 percent higher than the theoretical efficiencies. The departures from theory depend on the gamma-ray energy and the geometry of the shielding and collimators in such a way that it is not possible to provide a simple basis for relating theoretical efficiencies to the experimental data. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

It is the purpose of this paper to set forth the method and results of studying the gamma rays resulting from the bombardment of As75 with approximately 14 Mev neutrons. The source of these neutrons was the H3(d,n)He4 reaction. The deuterons of 325 Kev energy were obtained from a Van de Graff electrostatic accelerator. A NaI scintillation spectrometer was used to determine the gamma-ray energies.

No description available.

Call number: LD2668 .T4 1956 Y45 / Master of Science

Call number: LD2668 .T4 1979 N37 / Master of Science

published_or_final_version / abstract / Physics / Master / Master of Philosophy

<p align="justify">The success of Big Bang Nucleosynthesis (BBN) combined with the detailed analysis of the small imperfections of the Cosmic Microwave Background blackbody spectrum lead to the conclusion that most of the matter content of our universe is made of some non-baryonic material, the dark matter!</p> <p align="justify">In this thesis, we review the compiling indications of dark matter and the so-called freeze-out mechanism which may settle the relic density of the species in the framework of the standard Big Bang model. We also examine principally two methods of detection of dark matter, direct and indirect detection searches.</p> <p align="justify">Let us stress that the Standard Model on its own is unable to provide enough aspirants for the role of dark matter. As a consequence, one has to dig into the tremendous domain of physics "Beyond the Standard Model" in order to have a chance to elucidate the problem of the missing mass.</p> <p align="justify">In this thesis in particular, we consider the Inert Doublet Model (IDM) which includes an additional Higgs doublet, enclosing two neutral scalars candidates for dark matter. We invoke the Standard freeze-out mechanism for the production of dark matter. We get then dark matter candidates in two rather separate mass ranges, one between 40 and 80 GeV, the other one between 400 GeV and 1 TeV. We also show that dark matter annihilation at the galactic center can be at the origin of a gamma-ray flux which can be probed by the future GLAST experiment.</p> <p align="justify">We address a low reheating temperature scenario for the genesis of dark matter in a Left-Right symmetric extension of the Standard Model. The candidate for dark matter is a MeV right-handed neutrino and we show that a baryon-dark matter interaction at the galactic center can be the source of the low energy positrons responsible for the 511 keV gamma-ray excess observed by the INTEGRAL experiment in the galactic bulge region.</p> <p align="justify">Finally, prompted by the possibility to explain the baryon and dark matter rather similar abundances by one single "Matter Genesis" mechanism, we study a non-thermal production mechanism for dark matter. The framework is also Left-Right symmetric and dark candidate is a ~3 GeV right handed neutrino.</p>