Radiography in Modern Industry - Kodak

electrons by successive Compton interactions. Also, high-energy electrons pass out of anemulsion before all of their energy is dissipated. For these reasons there are, on the average, 5 to10 grains made developable per photon interaction at high energy.For comparatively low values of exposure, each increment of exposure renders on the averagethe same number of grains developable, which, in turn, means that a curve of net density versusexposure is a straight line passing through the origin (See Figure 131). This curve departssignificantly from linearity only when the exposure becomes so great that appreciable energy iswasted on grains that have already been exposed. For commercially available fine-grain x-rayfilms, for example, the density versus exposure curve may be essentially linear up to densities of2.0 or even higher.Figure 131: Typical net density versus exposure curves for direct x-ray exposures.The fairly extensive straight-line relation between exposure and density is of considerable use inphotographic monitoring of radiation, permitting a saving of time in the interpretation of densitiesobserved on personnel monitoring films.It the D versus E curves shown in Figure 131 are replotted as characteristic curves (D versus logE), both characteristic curves are the same shape (See Figure 132) and are merely separatedalong the log exposure axis. This similarity in toe shape has been experimentally observed forconventional processing of many commercial photographic materials, both x-ray films and others.Radiography in Modern Industry 205