PRODUCTION OF THE HYDRATED ELECTRON IN THE RADIOLYSIS OF WATER WITH HELIUM-IONS

The scavenged yield of the hydrated electron has been determined in the radiolysis of water with 2-22-MeV helium ions by measuring the production of ammonia from glycylglycine. Glycylglycine concentrations were 1, 0.1, 0.01, and O.001 M, which correspond to hydrated electron lifetimes of 3 ns to 3 mus, respectively. Differential hydrated electron yields were obtained from the observed energy dependencies, and for 1 M glycylglycine they ranged from 1.76 to 3.09 molecules/100 eV for 5-20-MeV helium ions, respectively. These values are slightly larger than the corresponding integral yields of 1.51-2.20 molecules/100 eV, respectively, but smaller than the yield of 3.81 found with fast electrons. In 0.001 M glycylglycine solutions the integral scavenged yield of the hydrated electron varies less than 1% per MeV of helium ion energy. At this concentration it was found that for 5-MeV helium ions the differential hydrated electron yield was 0.145 and the integral yield was 0.098 molecules/100 eV. These values are substantially less than the value of 2.47 molecules/100 eV found with fast electrons indicating the importance of intratrack reactions with helium ions in the nanosecond to microsecond time scale. It appears that the scavenged yields of hydrated electrons approach constant values with decreasing glycylglycine concentration for all helium ion energies studied. These lower limits are considerably less than the scavenged yields of hydroxyl radicals previously determined in formic acid solutions of comparable scavenging capacity.