COMPUTER-SIMULATION STUDY OF THE SENSITOMETRIC EFFECTS OF CORNER ROUNDING IN CUBIC GRAINS

Practical cubic grains have distinct rounding on their edges and corne rs. To a first approximation this rounding leads to a (111) crystallog raphic character at the corners. It is hypothesized that the different surface structures at the corners and faces of cubes lead to sensitiz er centers with different electronic properties-depth, density, and ca pture radius of traps. The effect of this difference in electronic pro perties for both AgBr and AgCl cubes is studied by computer simulation based on the nucleation-and-growth model of latent-image formation. F or AgBr, there is a large decrease in high-irradiance reciprocity fail ure (HIRF) and an overall increase in efficiency, if the sensitizer ce nters at the corners are assumed to be deeper electron traps with larg e trapping radii, but with low density, and the sensitizer centers on the face are assumed to be shallower electron traps with small trappin g radii, but with a high density. For other conditions with less diffe rence between corner and face sensitizer centers the sensitometric cha nges are not as large, but still significant. The decreased HIRF is at tributed to less competition between corner and face traps, and theref ore less dispersity. Similar results are seen in AgCl simulations. How ever, the initial HIRF of the AgCl control simulations is low because there is very little dispersity inefficiency at the low ionic conducti vity used in the AgCl simulations. When the large difference in electr onic properties of corner and face sensitizer centers is assumed, HIRF is removed and the efficiency increases to near that expected for a f ully efficient grain. This is attributed to the low hole mobility used in the AgCl simulations, which decreases recombination losses. For bo th AgBr and AgCl, the bimodal distribution in trapping properties prod uces a significant concentration effect in that all the latent image f orms at the grain corners. This leads to high efficiency, reduced HIRF , and reduced sensitivity of speed and contrast to inadvertent changes in development conditions.