Radiation chemical studies with heavy ions: oxidation of ferrous ion in the Fricke dosimeter

The yields for oxidation of ferrous ions in the Fricke dosimeter have been determined for 4He, 7Li, 9Be, 11B, and 12C ions with energies up to 35 MeV. These particles have a linear energy transfer (LET = -dE/dx) in water of up to 20 eV/A for 4He ions and 100 eV/A for 12C ions. For these high LET particles the radiation chemical yields for ferric production, which range from ∼ 3 to ∼ 8, are appreciably lower than for fast electrons (15.5). The differential yields determined from the observed energy dependences show that the yields are not uniquely determined by LET but increase with increased atomic number (Z) of the irradiating particle. Related measurements on deaerated solutions provide detailed information on the dependences of the H atom and water decomposition yields on particle type and energy and show that there is, at a given LET, increased diffusion of H atoms out of the track with increase in Z. However, at high energies this effect becomes relatively less important because of increase in the track radius. There is an indication that for heavy ions of very high energies the limit at low LETs may be well below the yield for fast electrons because energy is deposited in more dense spurs. The yield of H atoms which escape the track at the Bragg peak decreases from 0.30 for 4He ions to 0.09 for 12C ions. The low-energy limiting yields for particles of very high LET are less than 0.01 for H atom production and ∼ 2.8 for water decomposition. This report includes a comprehensive summary of previous studies of the Fricke system with heavy ion radiations