High chloride tabular grain emulsions and processes for their preparation

A radiation sensitive emulsion comprised of a dispersing medium and silver halide grains which are at least in part tabular silver halide grains bounded by {100} major faces

• wherein, of the tabular grains bounded by {100} major faces a portion accounting for 50 percent of total grain projected area selected on the criteria of adjacent major face edge ratios of less than 10 and thicknesses of less than 0.3 .mu.m and having higher aspect ratios than any remaining tabular grains satisfying these criteria (1) have an average aspect ratio of greater than 8 and (2) internally at their nucleation site contain iodide and at least 50 mole percent chloride.

A process of preparing silver halide emulsions in which tabular grains of less than 0.3 .mu.m in thickness exhibiting {100} major faces with adjacent edge ratios of less than 10 account for at least 50 percent of total grain projected area and internally at their nucleation site contain iodide and at least 50 mole percent chloride, comprised of the steps of

• (1) introducing silver and halide salts and a dispersing medium into a continuous double jet reactor so that nucleation of the tabular grains occurs in the presence of iodide with chloride accounting for at least 50 mole percent of the halide present in the dispersing medium and the pCl of the dispersing medium being maintained in the range of from 0.5 to 3.5 and
• (2) following nucleation completing grain growth in a reaction vessel which receives emulsion from the continuous double jet reactor under conditions that maintain the {100} major faces of the tabular grains.

A process of preparing a radiation sensitive emulsion containing a dispersing medium and silver halide grains, wherein at least 50 percent of total grain projected area is accounted for by tabular grains (1) bounded by {100}major faces having adjacent edge ratios of less than 10, (2) each having an aspect ratio of at least 2, (3) containing on average at least one pair of metal ions chosen from groups 8, 9 and 10, periods 5 and 6, at adjacent cation sites in their crystal lattice, and (4) internally at their nucleation site containing iodide and at least 50 mole percent chloride are prepared by the steps comprised of

• (a) introducing silver and halide salts into a dispersing medium so that nucleation of the tabular grains occurs in the presence of iodide with chloride accounting for at least 50 mole percent of the halide present in the dispersing medium and the pCl of the dispersing medium being maintained in the range of from 0.5 to 3.5,
• (b) following nucleation completing grain growth under conditions that maintain the {100} major faces of the tabular grains, and
• (c) during at least one of steps (a) and (b) introducing into the dispersing medium oligomers of group 8, 9 or 10, period 5 or 6, metal, wherein each oligomer contains at least two metal ions and on average at least two metal ions are incorporated in each grain in adjacent cation sites.