Theory of the Photodisintegration of the Deuteron and of Other Nuclei

Abstract

The interaction between the radiation field and a collection of nucleons is formulated in a manner suitable for the employment of the Franz-Stech classification of electromagnetic multipoles, and for separating the more certain parts of the interaction energy from the speculative ones, the uncertainties being concerned with exchange currents. The separation is effected by bringing the entrance of the electric charge density into evidence. The heuristic introduction of the intensity of magnetization as though it were due to magnetic moments of the fixed-magnetic-moment type is avoided, the whole interaction being expressed in terms of currents. Part of the general discussion neglects retardation so as to bring out the reasons for the particular grouping of terms, but retardation effects are included later on. It is shown that in a nonrelativistic theory the usual procedure of making calculations as though the center of mass of the $p-n$ system were fixed may be justified as an approximation provided certain assumptions are made. The recoil of the center of mass caused by photon absorption is explicitly considered in this connection. Some limitations of the theory caused by relativistic effects are mentioned. The relationships of contributions to the electric-multipole transition amplitudes caused by the nucleon magnetic moments, as well as of related contributions of radial components of the Schrödinger current, are discussed in relation to the retardation effects. A brief review of the limitations of space-time models and of the accomplishments of the pure $S$-matrix approach to the $d(\gamma ,n)p$ problem indicates the continued value of both approaches.