Directional Dependence of Exposure Measurements and the Evaluation of Effective Energies of Medium Energy X-rays by Film Badges

The previously proposed film badge used for exposure measurements as well as for the evaluation of the effective energy to which a film had been exposed, was checked for directional dependence between 0° and 80° when exposed to X-rays of effective energies between 23 and 138 keV. The angular dependence of the fractional net photographic densities Dtheta/D0 can be fitted by expressions which take into account mainly the absorption in the photographic layer and in the filters. In some cases an additional parameter is to be introduced. The density of the unfiltered portion of the film badge is almost independent of the angle of incidence in the entire range of effective energies studied. It can therefore be used for exposure measurements at angles up to 80°. The evaluation of the effective energy of X-rays for which die ratio of densities of the unfiltered and filtered portions D0/Dt are used, is not quite independent of the angle of incidence. Nevertheless, up to angles of 40° or even 50° it is possible to evaluate the effective energy. The error is negligible for angles up to 30° or 40°.