A Monte Carlo study of backscattering effects in the photoelectron emission into CH/sub 4/ and Ar-CH/sub 4/ mixtures

Monte Carlo simulation is used to investigate the backscattering and the transmission efficiency for the photoelectrons emitted from a CsI photocathode into CH/sub 4/ and Ar-CH/sub 4/ mixtures, for incident photons E/sub ph/ in the 6.8-9.8 eV (183-127 nm) energy range and applied electric fields from E/N=0.1 Td to E/N=40 Td. Due to vibrational excitation of CH/sub 4/, which starts at low electron impact energy, the addition of CH/sub 4/ to a noble gas increases electron transmission and drift velocity. The dependence of the transmission efficiency in CH/sub 4/ and Ar-CH/sub 4/ mixtures on the reduced electric field E/N, incident photon energy E/sub ph/ and mixture composition is analyzed, and results are compared with available experimental data.