Effects induced by electron beam in methane ices

The radiation effects and relaxation processes in solid CH₄ irradiated by an electron beam were studied with a focus on the beam-induced particle emission. The study was performed using cathodoluminescence (CL), monitoring of the total yield of particle emission and applying activation spectroscopy technique – thermally stimulated exoelectron emission (TSEE). Emissions of photons and particles under beam were monitored in a correlated style. Upon irradiation by 1 keV electron beam of 3 mA cm⁻² current density we observed for the first time explosive particle emission which occurred with the delay of an hour with respect to the start of irradiation. Simultaneously with the particles outburst a CL flash was detected. Delay in the giant outburst of particles indicates the need for the accumulation of radiolysis products for this phenomenon. The critical dose for this effect is 100 eV per methane molecule. The outburst of particles is preceded by oscillations of particles emission with increasing amplitude. The period of these oscillations depends on the intensity of the irradiation, it decreases with an increase in the beam current density. Possible mechanisms of low-temperature explosive particle emission are discussed.