Heavy ion radiolysis of methylene blue

Radiation chemical yields for the bleaching of aerated aqueous solutions of methylene blue in the radiolysis with γ-rays, protons and helium ions have been determined using absolute dosimetry techniques in order to promote this system as a chemical dosimeter with heavy ions. At low changes (<25%) in the initial absorption of 16 μM solutions, the dose response is reasonably linear for the radiations examined here. Radiation chemical yields for the bleaching of methylene blue solutions at 292 nm and at low doses range from 0.71±0.04 with γ-rays to 0.065±0.003 molecules/100 eV for helium ions. The yields decrease with decreasing proton energy, but seem to be independent of incident energy with helium ions. The results suggest that the overall efficiency for the decomposition of methylene blue by OH radicals is not directly proportional to the energy deposition density of the heavy ion.