Abstract

On of the earliest triumphs of quantum mechanics, when the theory was first formulated in the 1920s, was George Gamow's use of quantum tunneling to explain the phenomenon of alpha decay. It was well known then that certain heavy radioactive nuclei, including radium then widely used for glow-in-the-dark clock dials, would spontaneously and unpredictably spit out an energetic helium-4 nucleus (also called an alpha particle) and be transformed into a new lighter nucleus with two fewer nuclear charges. Alpha radioactivity is often very improbable, and this takes the form of alpha-decay half-lives measured in thousands or even millions of years. The question was, how and why did the alpha particle escape its prison in the nucleus, where it should have been tightly and permanently bound?