A Monte Carlo study of backscattering effects in the photoelectron emission from CsI into CH4 and Ar-CH4 mixtures

Abstract

Monte Carlo simulation is used to investigate photoelectronbackscattering effects in the emission from a CsI photocathode intoCH4 and Ar-CH4 mixtures for incident monochromatic photons withenergies Eph in the range 6.8 eV to 9.8 eV (182 nm to127 nm), and photons from a continuous VUV Hg(Ar) lamp with aspectral distribution peaked at Eph = 6.7 eV(185 nm), considering reduced applied electric fields E/N in the0.1 Td to 40 Td range. The addition of CH4 to a noble gasefficiently increases electron transmission and drift velocity, due tovibrational excitation of the molecules at low electronenergies. Results are presented for the photoelectron transmissionefficiencies f, where f is the fraction of the number ofphotoelectrons emitted from CsI which are transmitted through the gasas compared to vacuum. The dependence of f on Eph, E/N, andmixture composition is analyzed and explained in terms of electronscattering in the different gas media, and results are compared withavailable measurements. Electron drift parameters are also calculatedand compared with experimental data, confirming the choice of electronscattering cross-sections used in the simulations.