The Theory of Excitation Functions on the Basis of the Many-Body Model

Abstract

The theory of transmutation functions for charged particles is examined in the light of recent developments in nuclear theory. It is found that ignoring all factors besides the penetrability of the incident particle is justifiable only for processes without effective competition. For these, the usual applications of the Gamow-Condon-Gurney theory must be modified to include the influence of incident particles with nonvanishing orbital momentum which causes a continued rise of the yield for energies greater than the Coulomb barrier. For processes subject to effective competition, the comparative density of residual states available to each alternative process is important in determining relative yields. The densities of the states are calculated on the basis of the liquid drop model for the nucleus and a table is obtained giving the relative probabilities of neutron and charged particle emissions. The overwhelming factor in favor of neutron emission by heavy nuclei seems to be confirmed by experiment. The shape of an excitation curve expected for the less probable of two processes is shown. Finally the effect of selection rules in the yield curves of reactions involving very light nuclei is considered. Special cases are discussed.