Results of studies on the cobalt-60 y radiolysis of acidic cysteine (RSH) solutions, pH 1.0 and 0.5, are reported. Irradiation products which have been identified are H2, H2S, RSH, and H202 with radiation yields at 10 ~3 M cysteine of 3.2, 0.95, 3.0, and 0.68 molecules/100 eV absorbed. Alanine was also observed qualitatively as a radiation product. Yields for the disappearance of the thiol group were measured polarographically during the irradiation and (?(-RSH) was found to be 7.0 at 10-3 M cysteine. A mechanism is postulated for strongly acid cysteine solutions on the basis of competition kinetics, material balances, and comparison with theoretical yields. Analysis of results of competition studies provides evidence for a rate constant of approximately 3 X 10" 1. mol""1 sec-1 for the reaction of the hydrated electron with the protonated-amine form of cysteine. Results of scavenger studies at concentrations higher than 10~2 M cysteine require that additional processes be postulated in order to account for high H2S yields.

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