PHOTOGRAPHIC SILVER BROMOIODIDE EMULSIONS, ELEMENTS AND PROCESSES

PHOTOGRAPHIC SILVER BROMOIODIDE EMULSIONS, ELEMENTS AND PROCESSES A photographic silver bromoiodide emulsion comprises a dispersing medium and silver bromoiodide that (a) is octahedral silver bromoiodide; (b) has a grain size within the range of 0.45 to 1.2 microns; (c) contains 1 to 12 mole percent iodide; (d) has a core region (A), a surface region (B) and a subsurface region (C) between core region (A) and surface region (B); wherein (i) subsurface region (C) contains an iodide concentration higher than the iodide concentration of core region (A); and, (e) the silver bromoiodide is prepared by a process comprising, in sequence, (I) a nucleation step comprising mixing bromide or bromoiodide salts and silver salts in a reaction medium; then, (II) a crystal growth step under controlled pBr conditions within the range of 1.75 to 4.2 pBr enabling formation of core region (A) comprising 50% to 90% by weight of the silver bromoiodide; then, (III) addition to the composition from (II) of iodide salt in which 25 to 100 mole percent of the total iodide salt is added to the composition resulting from step (II) within a time period of 1 second to 20 minutes; then, (IV) holding the reaction mixture from step (III) for a time period of 0.5 second to 20 minutes that aids in formation of subsurface region (C); then, (V) addition of silver salts or the combination of silver salts and bromide to the reaction mixture from step (IV) until reaction completion forming surface region (B). Such photographic silver bromoiodide emulsions are useful in photographic silver halide materials to provide increased photographic speed of the materials.