Thermal stability of radiation-induced free radicals in γ-irradiated l-alanine single crystals

Decay of the radiation-induced stable free radicals in l-alanine single crystals and powders at the temperatures from 379 to 476 K was examined by electron paramagnetic resonance. For single crystals, the calculated activation energy of the radical decay is 104.3±1.7 kJ/mol (i.e. 12 538±202 K) and the frequency factor lnν0 is 24.1±0.4 min−1. The lifetime of the radical in single crystals at 296 K is 162 years. The results confirm the long-term stability of the radicals, but the decay was found to be faster in large crystals than in powders.