[en] The stability of methyl radicals formed in synthetic methane hydrate by γ-ray irradiation at 77K was studied at 200-273 K and 10 MPa. The methylradicals decayed under these conditions, despite the stability of methane hydrate, and changed into other molecules that could not be detected by electron spin resonance (ESR). Decay products were investigated by gas cell infrared (IR) spectroscopy by measuring the decomposed gas from the γ-irradiated methane hydrate. Only ethane molecules were detected from the irradiated sample, while these were absent in an unirradiated sample. The molar ratio of ethane to methane (C₂H₆/CH₄) was 12±1 ppm, which did not contradict with that of methyl radical to methane (CH₃^·/CH₄) in the literature. Hence, most of the methyl radicals generated by irradiation were supposed to be transformed to ethane in methane hydrate. (author)