Experimental and mechanistic studies of high dose rate radiolysis of dilute aqueous monochloroacetic acid solutions

The radiolyses of both deaerated and aerated dilute aqueous solutions of monochloroacetic acid (pH = 2.55) and monochloroacetate (pH approximately 7) have been studied with concentrations ranging from 10-2 to 10-3 M, dose rates from 1.19 x 1026 to 1.82 x 1028 ev/L/sec and pulse lengths from 0.35 to 6.1 microsecond. The absorbed total dose was up to 2.6 x 1020 ev/ml. Chloride and hydronium ions, produced primarily by the reactions of hydrated electrons and to a lesser extent by hydrogen atoms, were measured. The experimental results show that the product yields depend not only on solute concentration and pH, but also on dose rate. From these experimental results, a detailed reaction mechanism has been proposed for deaerated system based on the competition kinetics between radical-solute and radical-radical reactions as the result of higher radical concentrations at higher dose rates. The mathematical treatment for solving the simultaneous differential rate equations, based on computerized reiterative numerical analysis and integration, has also been reviewed and studied thoroughly. With the introduction of N2O, an electron scavenger, the G(Cl-) values decrease appreciably. However, with the introduction of oxygen, which is also an electron scavenger, the G(Cl-) values in low dose rate radiolyses are higher than those observed in corresponding deaerated systems. This experimental fact suggests an additional role of oxygen in the radiolyses of the system studied