Hydrogen Peroxide Production in the Radiolysis of Water with Heavy Ions

The radiation chemical yields of hydrogen peroxide in water at neutral pH have been determined with protons, helium ions, and carbon ions at energies of a few to 30 MeV. The long-time yields of hydrogen peroxide increase with increasing linear energy transfer, LET, for protons and helium ions, but it decreases for carbon ions due to higher order reactions within the particle track. However, the maximum increase in hydrogen peroxide yields is only about 50% from γ rays (LET = 0.2 eV/nm) to helium ions (LET = 156 eV/nm). Methanol was used as an OH radical scavenger in order to probe the temporal dependence of hydrogen peroxide formation. The differences in the time dependence of the formation of hydrogen peroxide with various ions are discussed and compared to that observed with γ rays.