Tagged photons

We consider in detail the differential cross sections for both polarized and unpolarized bremsstrahlung from electrons for angles and energies in the range of interest for a photon tagging system (50 MeV-1 GeV). We derive accurate high energy, small angle approximations to these cross sections. These approximations are then used to determine the maxima and minima of these cross sections as a function of the angles and energies of the final electron and photon and to evaluate them at the extrema. It is shown that the cross sections dσperpendicularto and dσparallel for the two polarization states as well as that for unpolarized photons each have a sharp dip in the region of small momentum transfers of the order of the minimum kinematically allowed momentum transfer. However, in this region the dependence of the cross sections dΣperpendicularto and dσparallel on the angles of the final electron and photon is quite different over most of the photon spectrum, and this results in rather large polarizations. Coulomb corrections to these Born approximation cross sections are considered; they do not fill in the dips. (orig.)