Photographic emulsions containing tabular grains with a band structure and a central grain portion of high bromide concentration

摘要

A radiation-sensitive emulsion comprises a dispersion medium and silver halide grains. At least 50% of the total grain projected are is accounted for by tabular grains of a face centred cubic crystal lattice structure having parallel (111) major faces, and average thickness of 0.2mu m and an average aspect ratio of >= 5, the tabular grains each being comprised of a central region and a shell differing in halide content. The central region contains > 50 mol.% bromide, based on silver forming the central region, the shell contains >= 60 mol.% chloride, based on silver forming the shell, and the shell is comprised of a band extending laterally outwardly from the central region and forming >= 2 (10)% of the (III) major faces, the band accounting for at least half the vol. of the shell. Pref. the tabular grains have an average thickness of 0.07mu m. The band accounts for >= 70 (80)% of the silver contained in the shell. The shell is comprised of detectable surface regions interposed between the central region and the (III) major faces. The central region comprises >= 70 mol.% bromide, based on silver forming the central region, the shell contains >= 70 mol.% chloride in the band, based on silver in the band.