Chemical Separation of Isomeric ⁸⁰Br Atoms

Abstract

FOR rather more than a year, we have been studying the concentration of radiobromine by modifications of the method of Szilard and Chalmers¹, and have been using concentrates to follow the kinetics of exchange reactions between radiobromine ions and alkyl bromides. In the course of this work, we have encountered a number of puzzling phenomena which are now completely explained by the remarkable discovery made by Segrè, Halford and Seaborg² and DeVault and Libby³ that the isomer of ⁸⁰Br with a half-life of 4.5 hours decays by a γ-ray change to an isomeric ⁸⁰Br which emits β-rays with a half-life of 18 minutes. The recoil from the soft γ-ray emitted by the parent nucleus (and its internal conversion) has been found sufficient to break a chemical bond in the BrO₃ anion or to activate tho C–Br bond in tertbutyl bromide and facilitate the hydrolysis of this compound. These reactions have been used to separate the isobaric 18-min. product from its parent 4.5-hour isomer with which it was previously in radioactive equilibrium. The β-ray activity of the daughter isotope in the reaction product was found to decay with a half-life of 18 min., whilst the activity of the residual bromine in the original reaction increased with time as the equilibrium concentration of the 18-min. isomer was restored by decay of the parent.