Isotopes

Abstract

THE subject of isotopes is particularly suitable for inclusion in this special issue of NATURE, for it is just twenty-five years since Soddy published the first valid proof of their existence. The earlier speculations of Crookes and others had been found to rest on unsound observations. Discussing apparent chemical identities among the products of radioactivity, Soddy said: “Chemical homogeneity is no longer a guarantee that any supposed element is not a mixture of several of different atomic weights, or that any atomic weight is not merely a mean number”. The basis of his evidence was the law connecting radioactivity and chemical change, in the discovery and enunciation of which he played so prominent a part. This law asserts that a radioactive element when it loses an α-particle goes back two places in the periodic table; when it loses a β-particle it goes forward one place. It follows that by the loss of one α-particle followed by two β-particles, the atom, though weighing four units less, will have regained its nuclear charge and returned to its original place.