Combined effects of high doses and temperature on radiation-induced radicals and their relative contributions to EPR signal in gamma-irradiated alanine.

Electron Paramagnetic Resonance (EPR) study of irradiated l-alanine showed differences in dose-response curves obtained at low and high microwave power for a broad range of doses, up to 3000 kGy. A mathematical model was fitted to experimental data and calculated yields of generation and of destruction of radicals showed variations with microwave power. The calculations were applied to both double integrals of the total EPR signal and to its components reflecting contributions of radicals R1, R2 and R3 in the alanine EPR signal. The relative contributions of radicals R1, R2 and R3 varied with dose >100 kGy; an increase in relative contribution of R3 was accompanied by a decrease in contribution of R1 radicals. The observed fading of EPR signal intensity in samples annealed to 175-208 degrees C was a strong function of dose, and varied by 2-3 orders of magnitude in the dose range examined.