Radiation Protection of Aqueous Polyvinylpyrrolidone Solutions by Thiourea

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Abstract
A detailed study has been made of radiation protection effects in a model macromolecular system—polyvinylpyrrolidone in water, with thiourea acting as the protecting additive. The effects of polymer concentration, dose-rate and additive concentration on the gelation dose have been determined. In the absence of polymer, dilute thiourea solutions show rapid destruction of thiourea on irradiation, with a smaller reduction in its subsequent protective ability. It is concluded that the major form of protection is offered by thiourea against the indirect effect of radicals produced in the water. Further protection occurs by H-transfer to polymer radicals; these constitute true protection, and the polymer is unaltered. Furthermore, thiourea can be linked into polymer giving a modified ‘stabilized’ product. The great ability of thiourea to protect, even at very low concentrations, is ascribed to the thiol-thione equilibrium in solution, which allows a chain reaction form of protection. This has been confirmed in a range of other additives.

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