Dispersion of latent image specks on reduction-sensitized emulsions

Abstract

The dispersion of latent image specks (LISs) on reduction-sensitized octahedral grain (Oct) and cubic grain (Cub) emulsions that were exposed to light of various intensity levels or to a 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 narrow distribution with a one-speck-per-grain pattern. This changed to a broad distribution for 1 s exposure, which obeyed the Poisson distribution law at the highest sensitization level. These suggested that there were P centres present acting as precursors of LISs and inducing dispersion. The distribution for high-intensity (10⁻⁴ s) exposure obeyed the Poisson law for sensitized Oct and Cub emulsions. This dispersion of LISs occurred even in absence of the effective electron traps, when the supply rate of photoelectrons was high.

The distribution of LISs was widely spread on exposure to α radiation, and the z and v_b values were calculated, where z was the number of LISs formed when an a particle hit a grain once and v_b was the number of LISs at which its linear increase with increasing number of striking a particles ceased and saturation began. Both z and v_b increased with increasing sensitization level for the Oct emulsions, while they were almost constant for the Cub emulsions. These reflected the increase in or the absence of P centres. It was also suggested that the photolytic Ag₃ speck is more effective than the Ag₂ P centre as an electron trap.

Keywords:

• dispersion
• latent image specks
• reduction-sensitized emulsions