Radiation-induced radicals in hydrated magnesium sulfate

Radiation-induced free radicals in hydrated magnesium sulfate, which are thought to be present on the surface of Europa, one of the Jovian moons, have been studied by electron spin resonance (ESR). ESR signals of both atomic hydrogen (H·) at g   = 2.0023 and sulfite radical (SO3−) at g = 2.0029 are observed in epsomite (MgSO4·7H2O) and in quenched samples of magnesium sulfate solutions, after gamma-ray irradiation at 77 K. Atomic hydrogen disappears at temperatures above 90 K. The sulfite radical starts to decay above 190 K in the quenched sample of 10% magnesium sulfate solution, whereas in epsomite, it is stable even at 260 K. The sulfite radical accumulates at low ambient temperatures, and is a promising candidate for estimating the age of hydrated magnesium sulfate, especially in extraterrestrial environments.

► Atomic hydrogen and sulfite radical are observed in hydrated magnesium sulfate. ► Sulfite radical are very stable even in quenched sample at low temperature. ► Sulfite radical is a possible candidate for dating in extraterrestrial regions.