THE EFFECT OF pH ON WATER RADIOLYSIS: A STILL OPEN QUESTION - A MINIREVIEW CHRISTIANE FERRADINIa and JEAN-PAUL JAY-GERINb* aLaboratoire de Chimie-Physique, UMR 8601 CNRS, Université René Descartes, 45, Rue des Saints- Pères, 75270 Paris Cedex 06, FRANCE bDépartement de Médecine Nucléaire et de Radiobiologie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke (Québec) J1H 5N4, CANADA; *corresponding author: FAX. 1-819-654-5442: email: jaygerin@courrier.usherb.ca Received 20 March 2000; accepted 8 May 2000 Abstract-- The available data describing the influence of pH on the radiolysis of liquid water are not current and still raise a certain number of problems. Especially for alkaline media, the question of the values of the primary free radical and molecular yields is yet unsolved, the experimental data appearing contradictory. It is proposed here to briefly summarize the main results that have been obtained on this subject thus far. In the quest of finding a definitive explanation for these apparent disagreements, Monte-Carlo simulation methods could offer a most valuable tool to further develop our understanding of pH effects in the radiation chemistry of water and aqueous solutions. The radiolysis of liquid water by y-rays, high-energy X-rays or accelerated electrons can be described by the following global reaction [1,2], written for an absorbed energy of 100 eV: where the coefficients are the so-called "primary" radical and molecular yields (RMY), representing the yields of radiolytic species at the homogenization time, that is, some 10-' s after energy deposition. For each 100 eV of energy deposited in the water, the reaction (1) indicates the number of eaq (representing the hydrated electron), H* and HO' free radicals formed, as well as the number of molecular products H2 and H202. G _H2o denotes, at this stage, the corresponding yield of decomposition of water. These values of the yields are connected by the relationships: