The response of photographic emulsions to electrons in the energy range 7-60 kev

The large-area responses of ten emulsions (five `conventional', three nuclear research and two Schumann-type) have been examined for electron energies between 7 and 60 kev. The responses are considered in terms of the initial slope of the optical density D -exposure E curve, the value of E for D = 1, the saturation density D s and the number of grains rendered developable per incident electron. For high D/D s values, the forms of the experimental ( D, E ) relationships are found to depart from those expected if the mechanism of rendering developable a photographic grain were a simple single hit process, in a way that depends on the electron energy. The effect on the single hit relationship of the dependence of the exposure on the depth of electron penetration is considered, allowing a more complete inter-pretation of the shape of the ( D, E ) curves in terms of simple descriptions of electron-grain interactions. The high sensitivities of the nuclear and Schumann emulsions make feasible the direct recording at useful magnifications of electron images formed by low energy electrons.