  Physicochemical properties of solid methane exposed to ionizing radiation
have attracted significant interest in recent years. Here we present new trends
in the study of radiation effects in solid methane. We particularly focus on
relaxation phenomena in solid methane pre-irradiated by energetic neutrons and
electron beam. We compare experimental results obtained in the temperature
range from 10K to 100K with a model based on the assumption that radiolysis
defect recombinations happen in two stages, at two different temperatures. In
the case of slow heating up of the solid methane sample, irradiated at 10K, the
first wave of recombination occurs around 20K with a further second wave taking
place between 50 and 60K. We also discuss the role of the recombination
mechanisms in burp phenomenon discovered by J. Carpenter in the late 1980s. An
understanding of these mechanisms is vital for the designing and operation of
solid methane moderators used in advanced neutron sources and could also be a
possible explanation for the driving forces behind cryo-volcanism on celestial
bodies.
