Reactions in tracks of high energy particles. Radiolysis of oxygen

Abstract

The present study attempts a completely a priuri calculation of chemical effects in an irradiated system. Oxygen was chosen for several reasons. It is a gaseous system composed of one type of atom and there is a chemical product which can be measured, ozone. It is also of practical interest and its radiation chemistry has been investigated experimentally. Finally, enough data were available for reasonable choices of the necessary constants. Theoretical description of an irradiated system involves solution of a set of coupled inhomogeneous partial differential eqilations. Any reasonably complete set of such equations is too complicated for solution by means other than a digital computer. In the present case the Univac 1107 in the University of Notre Dame Computing Centre was used. The range of pressures * between 1 and 100 atni was chosen for study. Track effects are not expected at the lower pressures, but at the higher pressures clustering of ions and parent-ion recapture of electrons must be considered as well as in- creased bimolecular reactions of intermediates. When the calculations got under- way it was found that for all rates of irradiation such that isothermal conditions could be maintained there was no significant overlapping of tracks. This situation is usually called the " low background " condition and tracks can be treated individually. On the basis of the computer calculations a simplified scheme was found to be approximately valid. The radiolysis of 02 in the lower pressure range to 10-3 atm was investigated by analytical means. It was known before the calculations were started that many of the experimental results were contradictory, and it was thought that an a priuri calculation would be of value in elucidation of the mechanism. The radiation-induced decomposition of 03 was found to be particularly difficult to consider. It is a chain process known to be affected by many trace impurities in the system. In this paper we only con- sider the 02 system in which a negligible amount of O3 has been formed. * In the calculations the pressure does not occur explicitly. We have used the term " pressure " in this paper as the pressure of perfect gas with the actual density of the system.