Tabular grain silver iodobromide emulsion of improved sensitivity and

Abstract

Silver iodobromide tabular grain emulsions of enhanced photographic sensitivity are disclosed. The silver iodobromide grains contain from 2 to less than 10 mole percent iodide, exhibit a coefficient of variation of less than 20 percent, and consisting essentially of tabular grains having opposed parallel major faces. Each of the tabular silver bromoiodide grains exhibit an iodide concentration in excess of 6 mole percent within a surface region extending to a depth of less than 0.02 .mu.m and exhibit a central iodide concentration of less than 2 mole percent. The tabular grain emulsion is prepared by providing within a reaction vessel a population of silver bromide or iodobromide host grains exhibiting a coefficient of variation of less than 20 percent and containing less than 2 mole percent iodide consisting essentially of tabular grains and introducing silver, bromide and iodide ions into the reaction vessel for deposition onto the major faces on the host tabular grains, with iodide ions accounting for at least 25 mole percent of total halide ions introduced.