Annealing Behaviour of Phosphorus-32 Recoils in Potassium Chloride Crystals

Abstract

The behaviour of radioactive species, formed by neutron capture in crystals, as a function of post-irradiation annealing treatment has been extensively studied for central atoms in oxy-anions^1,2. So far as we are aware, in only one case have annealing curves shown a lowering of the valency of the activated atom in the species resulting from dissolution of the crystal, namely in the case of the ⁷⁵As(n.γ)⁷⁶ As reaction in As₂O₃ and NaAsO₂ (ref. 3). In most cases there is a rapid rise in oxidation state of the readioactive species followed by a further slow rise or pseudo-plateau. Süe and Caillat⁴ found that heating neutron-irradiated sodium chloride for a few minutes to 350° C caused a significant increase in the proportion of lower-valency phosphorus-32. Since the colour of the irradiated crystals was simultaneously discharged they suggested that electrons from F centres might be effecting the reduction of phosphorus-32 + 5 species.