Relaxation processes in solid methane pre-irradiated with an electron beam

Highlights: • Radiation effects were studied by thermally stimulated activation spectroscopy. • Two peaks of relaxation emissions of electrons and particles indicate two stages of the relaxation. • Accumulation of negative charge in pre-irradiated methane films was first detected. The relaxation processes in CH₄ solids irradiated by an electron beam were studied with a focus on post-irradiation phenomena. Because of absence of thermally stimulated luminescence (TSL) from pure solid methane we applied current activation spectroscopy method – thermally stimulated exoelectron emission (TSEE). Two broad features were detected near 18 and 43 K. Their relative intensity appeared to depend on irradiation time. The experiments performed with a variable voltage applied to an electrode for current detection first revealed significant accumulation of uncompensated negative charge in pre-irradiated methane films. The TSEE current was detected at negative voltages up to −35 V. Concurrently with thermally stimulated yield of electrons the total yield of thermally stimulated post-desorption (TSpD) from pre-irradiated solid methane film was detected. Correlation of TSEE and TSpD yields is discussed and compared with the temperature behavior of solid methane subjected to a neutron flux.