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Includes abstract. Bibliography: leaves (8-1)-(8-10)

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Thomas K. Gaisser, Dept. of Physics & Astronomy. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

A prompt-gamma, neutron-activation analysis facility earlier developed at the Nuclear Science Center of Texas A&M University could not be used successfully to analyze geologic samples due to high detection background, low neutron fluence rate and poor detection equipment . A systematic investigation into the performance capability of a prompt-gamma, neutron activation analysis facility was undertaken in this research project. The facility was reconstructed and used to obtain prompt-gamma spectra of chlorine and cadmium and from the spectra, the net peak area counts for the most intense prompt-gamma-ray energies were obtained. A theoretical model was developed which can predict the net peak area counts expected on these prompt-gamma-ray energies using the thermal neutron fluence rate at the sample position, the absolute efficiency of the detector, and the mass and partial gamma-ray production cross section data for the samples. The experimental and predicted results were compared to establish the performance capability of the reconstructed facility. Good agreements between experimental and predicted results were obtained for chlorine, but results from cadmium showed larger discrepancies due to self-shielding effects. Corrections for self-shielding effects were applied to results from cadmium and the experimental and predicted results were also in good agreement. The satisfactory results indicate that it is possible to implement the prompt-gamma, neutron-activation analysis technique at Beam Port #1 of the Nuclear Science Center Reactor. To be able to obtain excellent results from other samples, improvements in shielding materials to attain a lower detection background and a highly efficient detection system should be incorporated.

A prompt-gamma, neutron-activation analysis facility earlier developed at the Nuclear Science Center of Texas A&M University could not be used successfully to analyze geologic samples due to high detection background, low neutron fluence rate and poor detection equipment . A systematic investigation into the performance capability of a prompt-gamma, neutron activation analysis facility was undertaken in this research project. The facility was reconstructed and used to obtain prompt-gamma spectra of chlorine and cadmium and from the spectra, the net peak area counts for the most intense prompt-gamma-ray energies were obtained. A theoretical model was developed which can predict the net peak area counts expected on these prompt-gamma-ray energies using the thermal neutron fluence rate at the sample position, the absolute efficiency of the detector, and the mass and partial gamma-ray production cross section data for the samples. The experimental and predicted results were compared to establish the performance capability of the reconstructed facility. Good agreements between experimental and predicted results were obtained for chlorine, but results from cadmium showed larger discrepancies due to self-shielding effects. Corrections for self-shielding effects were applied to results from cadmium and the experimental and predicted results were also in good agreement. The satisfactory results indicate that it is possible to implement the prompt-gamma, neutron-activation analysis technique at Beam Port #1 of the Nuclear Science Center Reactor. To be able to obtain excellent results from other samples, improvements in shielding materials to attain a lower detection background and a highly efficient detection system should be incorporated.

published_or_final_version / Physics / Master / Master of Philosophy

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Entre los problemas más importantes de la astrofísica se destaca la falta de una clara identificación para las fuentes detectadas a muy altas energías (>100 MeV) por telescopios satelitales. En la actualidad, detecciones a energías más altas aún (>200 GeV) están siendo obtenidas por telescopios Cherenkov. En combinación con estudios multifrecuencia, estas observaciones plantean numerosos desafíos teóricos. Entre las posibles contrapartes de las fuentes gamma galácticas, los sistemas binarios con acreción brindan excelentes perspectivas, a las que se suma la reciente detección en el rango TeV de 4 binarios de rayos X. En la presente investigación doctoral nos hemos focalizado en la emisión gamma originada en binarias de gran masa con acreción, debido a la interacción de protones relativistas con el medio local. Dicho proceso genera radiación gamma a través del decaimiento de los piones neutros que se crean en las colisiones pp. Específicamente, hemos estudiado el caso de un objeto compacto de bajo campo magnético, capaz de efectuar eyecciones de masa confinadas en chorros de partículas relativistas (microcuásares). En este contexto, hemos explorado también la emisión leptónica secundaria. Dentro de los jets se generan pares relativistas al decaer piones cargados, que son otro subproducto de las colisiones pp. Se resolvió en forma consistente la evolución de esta población de pares, teniendo en cuenta las pérdidas de energía radiativas y adiabática, y se calculó su emisión sincrotrón y Compton inversa.