TRACK EFFECTS IN THE RADIOLYSIS OF WATER - HO2. PRODUCTION BY 200-800-MEV CARBON-IONS

The production of HO2. in the radiolysis of ferrous sulfate-cupric sulfate solutions, which provides a sensitive measure of intratrack processes in water, has been determined for carbon ions having energies of 200-800 MeV. The differential yield is found to decrease from 0.047 molecules/100 eV at 200 MeV (linear energy transfer (LET) = 110 eV/nm) to 0.028 molecules/100 eV at 800 MeV (LET = 36 eV/nm). Studies in this energy region permit.a direct comparison between the intratrack processes of carbon ions and of protons having the same LET. At the highest carbon ion energy the differential yield of HO2. is still 40% greater than that found with fast electrons (0.020 molecules/100 eV) but only 60% of that for protons of the same LET. In general, it is found that the yields of HO2. are similar for carbon ions where the LETs are 3-fold greater than those of protons. This difference reflects the expansion of the track resulting from the greater velocity of the more highly charged particles.