Comparison of theory and experiment for polarizational bremsstrahlung

Portillo and Quarles have recently observed significant deviations from ordinary bremsstrahlung predictions for bremsstrahlung from gas targets, after not seeing such effects in solids. These deviations are interpreted as an observation of the polarizational bremsstrahlung component. We review previous discussion of this component. No adequate theory is presently available for the angular dependence of the bremsstrahlung cross section being measured in these new experiments. We examine the validity of the simple estimates which Portillo and Quarles have tried to use.