FUNDAMENTAL CONSIDERATIONS OF DENSITY-THICKNESS CURVES FOR SOFT-X-RAYRADIOGRAPHS

We consider the fundamental issues of density-thickness curves, which express the contrast and the latitude of soft X-ray radiographs. First ly, soft X-ray spectra for various thicknesses of polyester objects we re obtained experimentally and attenuation curves of X-ray exposure, d efined by the ionization of air, were derived. As a soft X-ray radiogr aph is usually exposed directly, without a screen, the energy absorbed in the emulsion layers was supposed to be more suitable to describe t he input to an X-ray film than the total X-ray exposure used hitherto. Secondly, X-ray absorption efficiency spectra of emulsion layers of X -ray films were measured and attenuation curves of energy absorbed in the emulsion layers were obtained. Thirdly, density-thickness curves w ere derived, by combining the characteristic curve of an X-ray film wi th the two kinds of attenuation curves, and compared with those of rad iographs of a polyester step wedge. As a result the energy absorbed in the emulsion layers was shown to be more suitable to describe the inp ut to an X-ray film than the total X-ray exposure.