Tabular grain silver halide emulsions, a method for their preparation and photographic products

摘要

A photosensitive emulsion is disclosed comprised of a dispersing medium and silver halide grains containing at least 80 mole percent bromide, based on silver, wherein at least 50% of the projected area of said silver halide grains is accounted for by tabular grains free of twin planes having {100} parallel major faces, said emulsion being chemically sensitized and having a reciprocity failure of less than 35 sensitivity units between exposures of respectively 10-5 seconds and 100 seconds. The emulsion can be employed as a latent image forming emulsion in a photographic element. The emulsion can be prepared by a process preparing a silver bromide photosensitive emulsion, comprising the following essential steps: (a) a nucleation step whereby a fine-grain emulsion with a pAg of between 4 and 6.5 and a pH of between 2 and 5 is precipitated, while maintaining, at the start of the nucleation and for a short time, a stoichiometric excess concentration of silver corresponding to a pAg of less than 5, and (b) a physical ripening step, at a pAg of between 8 and 9.5 and a pH of between 6 and 8.