XXX.Special mechanisms in the reaction7Li(pγ)8Be

Abstract

The course of the reaction ⁷Li(pγ)⁸Be is an unusual one: above the strong resonance at E_p =440 kev the cross section shows a background that, apart from weak resonances, increases steadily with increasing proton energy until at least E_p = 5·2 mev. It is suggested that this background has two origins: at the lower values of E_p it is due to direct radiative transitions between a free proton state and a bound state of ⁸Be—no compound nucleus is formed; at the higher values of E_p it is due to a process inverse to the familiar ‘giant resonances’ of photo-disintegration. The first contribution is calculated for a variety of conditions in LS and in jj coupling; the second is deduced from the known properties of neighbouring photodisintegration cross sections. The two processes together give a good account of the experimental results; there is some suggestion that the ‘radius’ of ⁸Be may be about 3·2 × 10⁻¹³ cm.