Dispersion of latent image specks on reduction-sensitized emulsions

The dispersion of latent image specks( LISs) on reduction-sensitized octahe dral grain (Oct) and cubic grain (Cub) emulsions that were exposed to light of various intensity levels or to ct radiation was studied. The number and distribution of LISs on a grain were determined with arrested development or gold deposition techniques. The sensitized Oct emulsions were sensitive to extra-low-intensity (24 or 48 h) exposure. This exposure displayed a nar row distribution with a one-speck-per-grain pattern. This changed to a broa d distribution for 1 s exposure. which obeyed the Poisson distribution law at the highest sensitization level. These suggested that there were P centr es present acting as precursors of LISs and inducing dispersion. The distri bution for high-intensity ( 10(-4) s) exposure obeyed the Poisson law for s ensitized Oct and Cub emulsions. This dispersion of LISs occurred even in a bsence of the effective electron traps, when the supply rate of photoelectr ons was high. The distribution of LISs was widely spread on exposure to cw radiation. and the z and nu (b) values were calculated, where z was the number of LISs fo rmed when an a;particle hit a grain once and nu (b) was the number of LISs at which its linear increase with increasing number of striking alpha parti cles ceased and saturation began. Both z and nu (b) increased with increasi ng sensitization level for the Oct emulsions, while they were almost consta nt for the Cub emulsions. These reflected the increase in or the absence of P centres. It was also suggested that the photolytic Ag-3 speck is more ef fective than the Ag-2 P centre as an electron trap.