The formation of hydrogen peroxide in water by ionizing radiation
Shalek, Robert J.
Doctor of Philosophy
The free radical theory of the indirect action of radiation, though not completely satisfactory, has survived nearly 10 years since it was postulated by Weiss in 1944. The suggested mechanism is as follows: (1) The primary act is the ionization of a water molecule. H2O→radiation H2O++e- (2) The electron travels to a distance where it reacts with another water molecule. e-+H2O→H+OH- (3) The heavier H2O+ remains near the original site, splitting into a neutral and a charged particle. H2O+→H++OH The overall reaction can be written: H2O→radiationH+OH It is estimated that the H and OH are formed about 2 x 10 -6 cm apart. Thus with a densely ionizing particle many OH radicals are formed near each other and the H radicals appear in a cylindrical sheath of 5 x 10-6 cm mean radius. In this case the formation of hydrogen peroxide is favored. Admitting the possibility of intermediate steps, the reaction can be written: OH+OH→H2O2 With particles of lower linear ion density, it is presumed that the OH radicals are formed at a distance comparable to, or greater than the distance separating the H and OH and that then the recombination is favored H+OH→H2O For this reason no H2O2 appears in pure oxygen-free water with X- and gamma-rays at moderate dose rates. In the work to be presented here, the free radical hypothesis is neither proved nor disproved. However, as will be pointed out later, other mechanisms can be postulated to explain the experimental findings.