Recoil-Atom Reactions at Low Temperature

Abstract

CHEMICAL effects attending transformations of the nuclei of atoms in solids have been observed in a large number of systems¹. Such effects are attributed to nuclear recoil, inner shell ionization followed by an Auger cascade, or nuclear charge change, for example in β-decay. Atoms which have transformed may be found in their original chemical form² or in altered chemical states. The percentage of radioactive atoms found in the original chemical form has been called the ‘retention’ by Libby². A recoil atom of the latter type may be considered a defect in the crystalline lattice, and in analogy with thermal annealing reactions of defects, for example interstitial atoms, produced by heavy particles of γ-ray bombardment³, the application of heat to crystals containing recoil atoms frequently changes the observed distribution of chemical species¹. In general, annealing reactions of recoil atoms tend to restore those atoms to their original (‘parent’) chemical form. Recoil reactions following slow neutron capture are known as Szilard–Chalmers reactions, after the discoverers of this effect⁴.