Electrical Measurements on Photographic Emulsion Grains. I. Dark Conductivity

Abstract

By exposing with light flashes delayed by short time intervals after the application of electric field pulses, it is possible to measure ionic conduction on large silver bromide grains from a photographic emulsion. Values of conductivity were obtained by an analysis of the transient decay of internal field pulses resulting from the application of known pulses of the external field. The internal field was measured by means of its effect in causing displacement of latent-image centers formed by the exposure flashes. The room-temperature ionic conductance of these grains was found to be the equivalent of about 9×10−6Ω−1 cm−1 with an activation energy of about 0.42 ev. This conductance is several powers of ten higher than that reported for large silver bromide crystals of high purity and is thought to be primarily the result of surface effects. The implications of this result in terms of modern theories of photographic latent-image formation are discussed.