Early production of radicals from charged particle tracks in water.

An overview is presented of the early production of water radicals due to the passage of fast charged particles. It starts with energy deposition in tracks followed by the time scale of events of importance to radiation chemistry and radiobiology. Primary radical yields and reaction schemes, considered independent of particle LET but functions of the phase of the medium, are discussed within the framework of diffusion kinetics. Taking these primary G values (i.e., 100-eV yield) of OH, e-aq, and H as 5.70, 4.78, and 0.62, respectively, in liquid water, simple examples are provided for the evolution of the radical species. Finally, attention is drawn to some special physical features of fast, heavy charged particle tracks.