Study of Solid State Exchange of 131I-Doped in KIO by Radio Paper Chromatography

Abstract

The chemical change of 1311-dopants are studied in KI03 using radio paper chromatography. Isothermal and isochronal transfer annealing reveal that the conversion of 1311-into 131IO3is initially sharp, leading to a temperature-dependent pseudo-plateau, and follows a first-order kinetics with an activation energy of 0.35 eV. The decrease in the total radioactivity of the doped samples upon heating in tubes open to atmosphere signifies the formation of a volatile intermediate, i.e., iodine. The importance of iodine vapour in the transfer annealing process is manifested by the higher yield of131IO-3when the doped samples are heated in sealed tubes. The yield of 131IO-3is found to be higher when the doped samples after heat treatment were dissolved in alkaline aqueous media than after dissolution in acidic aqueous media. The mechanism envisages, first, the formation of solid state lattice precursors induced by heat and inherent crystal defects. Later, these lattice precursors undergo either combination reactions to produce volatile iodine or exchange reactions with other isotopic species of the host lattice or hydrolytic/oxidation reactions upon dissolution in aqueous media. The roles of iodine vapour and effect of pH have been discussed. © 1992, R. Oldenbourg Verlag