ESR investigation of γ-irradiated natural methane hydrate from Blake Ridge Diapir, off east North America in ODP Leg 164

Natural methane hydrate under deep ocean floor in Ocean Drilling Program (ODP) Leg 164 was studied by electron spin resonance (ESR) after γ-ray irradiation. The methyl radical (g=2.0024±0.0005, A=2.3±0.1mT) as well as an unidentified signal was observed. Although the parameters and the thermal stability were very similar to those in a synthetic sample, the signal intensity was about one eightieth of that in synthetic one because methane hydrate had partially changed to ice. ESR signal intensity of the methyl radical after γ-ray irradiation could be used to estimate the amount of methane hydrate in a sample mixed with ice.