Influence of Ionizing Radiation on Thermal Annealing in the Crossover Region of Potassium Chromate

Abstract

ISOTHERMAL annealing curves for the formation of Cr(VI) from Cr(III) in K2CrO4 appear to have a similar form for recoil chromium-51 produced by the 50Cr(n,γ)51Cr process and for chromium-51 introduced as dopant 51Cr(III) during crystallization of the potassium Chromate1–3. Recent studies of the Cr(III) species themselves, however, reveal that the low temperature (0°–100° C) annealing behaviour of these species is significantly different when the irradiated crystals have been recrystallized before annealing, as compared with crystals which are annealed directly4. It has been suggested4,5 that the “crossover reaction”, characterized by a conversion of Cr(III)-dimer + polymer species to Cr(III)-monomer species during annealing in the temperature range 0°–100° C in neutron-irradiated K2CrO4, may be related to either the presence of radiation-produced bulk structural and/or electronic species, or to local damage created by the recoil atom itself, or both. We now have evidence that the “crossover reaction” is not sensitized by bulk radiation-produced defects.