The collision of α-particles with atomic nuclei

Abstract

Since the introduction of the concept of nuclear potential barriers by Gurney and Condon and by Gamow a great deal of attention has been concentrated on the behaviour of such systems. As a consequence of this there has been a considerable increase of knowledge of nuclear phenomena, particularly in so far as these are concerned with α-particles. As a great proportion of experimental investigations in nuclear physics are concerned with the observation of effects due to impacts of α-particles on nuclei, the theoretical investigation of such collisions is of great interest. In this connection difficulties arise owing to the strong perturbation of the α-particle wave by the nuclear potential barrier. This renders the ordinary theory of collisions, due to Born, inapplicable and this failure of the usual theory was not realised for some time. A more suitable theory has never been developed explicitly, though formulæ which one would expect to derive from such a theory have been used. In this paper a suitable theory is developed. Besides establishing the validity of the above formulæ, this theory is also applied to the consideration of the probability of α-particle exchange on impact and to the elastic scattering by light nuclei (Mg, Al, etc.). It is shown that α-particle exchange is of considerable importance when the energy of the incident α-particle coincides with that of a virtual level of the nucleus and will have the effect of broadening the level.