Coulomb Excitation

Abstract

According to most of the present evidence nuclear forces have a relatively short range and such theoretical speculations as exist regarding their origin are in agreement with this view. Nuclear reactions depending exclusively on the action of such forces may be expected, therefore, to be practically absent if the projectile and the target have insufficient kinetic energy of relative motion to be brought nearly in contact with each other. The electromagnetic field of a charged particle falls off with distance more slowly than the specifically nuclear forces and is thus capable of raising a target nucleus from its ground level to a higher one at bombarding energies which are so low as to make reactions taking place by other mechanisms entirely negligible. Under these conditions it is customary to refer to the excitation which takes place as Coulomb excitation. This mechanism of excitation has also been observed to combine itself at higher bombarding energies with other types of nuclear reactions. In such cases one also speaks of Coulomb excitation when referring to the electromagnetic part of the process. If a distinction has to be made the first process is referred to as pure Coulomb excitation. This phenomenon has proved very useful in providing values of electromagnetic transition moments and in this manner has been instrumental in the development of the collective particle nuclear model and its unification with the shell theory of nuclear structure¹.