Nuclear Photoprocesses at High Energy

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In view of recent interest in the influence of pion production on the high energy photonucleon cross sections, an attempt is made to give a systematic discussion of the background effects, i.e., those high energy effects which are not directly concerned with either the production of pions or relativistic corrections to the nucleon motion. An appropriate definition of each high energy (irreducible) multipole moment is given. It is shown that the Siegert theorem does not apply, so even the electric dipole transition may be affected by (adiabatic) exchange currents. These and other high energy effects are found to contribute about 5 percent to the electric dipole photodisintegration cross section of the deuteron. Larger corrections are anticipated for heavier nuclei. It is shown that the corrections are calculated most readily by using the usual form of the multipole moment operators, rather than the formally correct irreducible operators.