EPR Studies on Trapped Species Produced by Tritium β Particles in Alkaline and Acid Ices at 77°K

EPR studies were performed on 60Co γ-irradiated 6M and 10M NaOH and 11M H2SO4 frozen solutions at 77°K and on similar frozen solutions which were tritiated with T2O. The yield of trapped species was always larger in the γ-irradiated systems than the corresponding yield in β-irradiated systems. The γ / β yield ratios were in semiquantitative agreement with similar ratios in liquid solutions. This is discussed in terms of different mean linear energy transfer for tritium β and 60Co γ radiation. Paramagnetic relaxation studies versus radiation dose were carried out on the tritiated systems and compared with previous results on γ-irradiated systems. For trapped H atoms in acid ice a spatially uniform distribution was found for both β and γ radiolysis. Trapped electrons in alkaline ice show a nonuniform distribution for γ radiolysis characterized by a finite spur radius. The distribution is also nonuniform in β radiolysis, but the average spur radius is larger. Surprisingly, the local concentration of trapped electrons appears smaller in β compared to γ radiolysis. A greater fraction of overlapping spurs in β radiolysis can account for these results.