Annealing reactions in potassium chromate. Part 1.—Processes involving recoil 51Cr(III) species

Abstract

Isothermal and isochronal annealing of neutron activated K₂CrO₄ was investigated by measuring the ⁵¹Cr distribution among aqueous ⁵¹Cr(VI), ⁵¹Cr(III)-monomer, ⁵¹Cr(III)-dimer and ⁵¹Cr(III)-polymer species following dissolution. Annealing occurring in the temperature range from –8° to 240° is tentatively attributed to a set of reactions involving at least five crystal phase ⁵¹Cr-containing species. Electrons, holes or other irradiation produced species in the bulk crystal appear to participate only in reactions occurring below 100° where little annealing to ⁵¹Cr(VI) occurs. The principal reaction in this range is a conversion of dimer-forming species to monomer-forming species. Below 180°, ⁵¹Cr(III)-monomer-forming species do not produce appreciable ⁵¹Cr(VI). Above 180°, part of the ⁵¹Cr(III)-monomer-forming species is rapidly converted to ⁵¹Cr(VI) while the remainder is converted to ⁵¹Cr(VI) at the same relative rate as is the remaining ⁵¹Cr(III)-dimer-forming species.