Radical formation in the radiolysis of solid alanine by protons and helium ions

Radical formation in solid alpha-alanine irradiated with 0.5-, 1-, 2-, and 3-MeV H+, 0.5-, 1-, and 3-MeV He+ ions were studied by means of electron spin resonance. The radical yield (number of radicals per incident ion) is constant below the critical fluence of about 10(12) ions cm(-2). Above the critical fluence, the yield decreases with increasing ion fluence, G-value of the radical formation was obtained from the constant yield at the low fluences, Assuming a simple cylindrical shape of the ion tracks, the average radii of the ion tracks were estimated from the G-values, The estimated value of the radius is from 2 nm to 5 nm, The dependence of the radical yield on the ion fluence was simulated with the cylindrical model of ion tracks and dose-yield relationship for gamma-irradiation. The observed yield decreases more than the simulated one above the critical fluence. This difference is ascribed to higher damage on the solid alanine by the ion irradiation than by gamma-irradiation.