Radiochemical Transformation of High Pressure Methane under Gamma, Electron, and Neutron Irradiation
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The chemical effects of irradiation on high pressure methane and noble gas mixtures were investigated using gamma, electron beam, and neutron irradiation sources. The gamma source used was the La-140 source from the Nuclear Science Center (NSC) at an activity of 400 Ci. The electron source was a 10 MeV, 15 kW, linear accelerator at the National Center for Electron Beam Research. The neutron source was the NSC reactor running at 1 MWth. The in-core positions were used for the neutron irradiations had neutron fluxes ranging from 5 x 10^(12) to 1x10^(13) n/cm^(2)/s. The gases used for the study included research grade methane, argon, and helium. The compressed gases were irradiated in a several separate irradiation vessels made with minimal nonmetal parts to reduce contamination. The majority of the vessels were pressurized to 2.07 MPa (300 psi) for the irradiation. The vessels were irradiated by one of the three irradiation sources for a maximum dose. The methane was mixed with the noble gases helium and argon, these gases were added to dilute the methane concentration, and study charge transfer effects on radiation chemical yields. The reaction products were measured using a gas chromatography mass spectrometer (GCMS). In addition to the GCMS, a lab made mass spectrometer system was used to measure the hydrogen and ethane concentrations within the gas post irradiation. The NSC Reactor irradiations show a measurable increase in the concentration of ethane and hydrogen, the La-140 and electron beam irradiations do not show measurable increases in hydrogen and ethane concentrations. The primary accomplishment of this research was the design of systems that are capable of performing high pressure gas irradiations. The irradiation experiments devel-oped three separate irradiation vessels during the course of the experiments. The analysis system was a mass spectrometer system that is capable of trace molecule detection. The experiments that had shown measurable change in the hydrogen and ethane concentra-tions had the G-values of the individual reaction products calculated for the NSC reac-tion irradiations. The G-values for were calculated to be 2.61±0.62 and 1.16±0.34 for hydrogen and ethane production, respectively. The effects of different types of radiation were examined during this thesis, and a future experimental work is proposed.
Clemens, Jeffrey Tyler (2014). Radiochemical Transformation of High Pressure Methane under Gamma, Electron, and Neutron Irradiation. Master's thesis, Texas A & M University. Available electronically from