Chemical effects of thermal neutron capture. Radiation and thermal annealing reactions in single crystals of potassium chromate

Abstract

The radiation and thermal annealing of neutron-activated single crystals and polycrystalline K₂CrO₄ has been investigated by measuring the ⁵¹Cr distribution among aqueous ⁵¹Cr(VI), ⁵¹Cr(III)-monomer, and ⁵¹Cr(III)-dimer species following dissolution. Radiation annealing up to 75 Mrad doses and thermal annealing in the temperature interval –78° to 300°C are attributed to at least seven crystal phase ⁵¹Cr-containing species. Six well-separated thermal annealing reactions occur between –78° and 300°C in single crystals receiving a γ-dose less than 1 Mrad during reactor irradiation. The fine structure of the thermal annealing curves is lacking in polycrystalline K₂CrO₄ and in single crystals receiving more than 3-4 Mrad in pile γ-dose. Three radiation annealing reactions take place in both polycrystalline and single crystals of K₂CrO₄ for doses up to 75 Mrad, but the reactions are different at low doses (0-5 Mrad) in the two types of crystals. The annealing eactions have been studied both in the presence and absence of air. The influence of the annealing atmosphere depends to a large extent on the crystal perfection.