Converted-halide photographic emulsions and elements having composite silver halide crystals

A converted-halide silver halide photographic emulsion comprised of a photographic vehicle as a continuous phase and, as a discrete phase, radiation-sensitive composite silver halide crystals each comprised of

• beta-phase truncated bipyramid silver iodide crystals having a minimum mean diameter of at least about 0.2 micron,
• in each composite crystal at least one converted-halide silver halide crystal forming an epitaxial junction with the silver iodide crystal,
• at least half of the facets of the silver iodide crystal being substantially free of epitaxial converted-halide silver halide and
• the converted-halide silver halide crystals being limited to from 1 to less than 50 mole percent, based on the total silver halide forming the composite silver halide crystals, the converted-halide silver halide crystals being comprised of at least 80 mole percent silver bromide and less than 5 mole percent silver iodide, the remainder being silver chloride.

In a photographic element comprised of a support and, as a coating on the support, a radiation-sensitive layer including radiation-sensitive silver halide crystals,

• the improvement wherein at least a portion of the radiation-sensitive silver halide crystals are composite silver halide crystals comprised of
• multi-faceted, radiation-receptive silver iodide crystals,
• converted-halide silver halide crystals at least partially converted from silver chloride to silver bromide forming epitaxial junctions with the silver iodide crystals,
• at least half of the facets of the silver iodide crystals being substantially free of epitaxial silver chloride, and
• the converted-halide silver halide crystals being limited to less than 75 mole percent, based on the total silver halide forming the composite crystals.

In a photographic element comprised of a support and, as a coating on the support, a radiation-sensitive layer including radiation-sensitive silver halide crystals,

• the improvement wherein at least a portion of the radiation-sensitive silver halide crystals are composite silver halide crystals each comprised of
• beta-phase truncated bipyramid silver iodide crystals having a minimum mean diameter of at least about 0.2 micron,
• in each composite crystal at least one converted-halide silver halide crystal forming an epitaxial junction with the silver iodide crystal,
• at least half of the facets of the silver iodide crystal being substantially free of epitaxial converted-halide silver halide and
• the converted-halide silver halide crystals being limited to from 5 to less than 50 mole percent, based on the total silver halide forming the composite silver halide crystals, and the converted-halide silver halide crystals being comprised of at least 80 mole percent silver bromide and less than 5 mole percent silver iodide, the remainder being silver chloride.