Author Institution: Aerospace Research Laboratories, Wright-Patterson Air Force Base, OhioA method is presented for the determination of the effective average projected grain diameter (d-a) using visual analysis of enlargements of Kodak Tri-X Pan and Kodak Royal-X Pan emulsions. Each was exposed to three light sources of color temperatures 6100°K, 2850°K, and 2040°K, and was developed in Kodak developers HC-110, DK-50, and D-19 for 5, 8, 12, and 20 minutes at 68°F. For 5- to 20-minute developing times, dA was determined, from a total of over 12,000 counts, to be from ~ 2.1 to ~ 2.4 u for both films. A method for calculating the conversion yield -q (number of grains to total number of quanta focused on the emulsion) is derived. The value y is a function of film density (D); it was found that rj first increases and then decreases, and a theory which explains this behavior in connection with grain formation is proposed; that is, 77 is the result of a superposition of an increasing and a decreasing function. The first is caused by the fact that a photographic nucleus made up of three silver atoms has a lesser probability for development than a four-atom nucleus, where with the increased exposure (number of quanta per unit area), the ratio increases in favor of the latter, resulting in an increasing function. However, the photographic plate, unlike the photoemitter, is a "non-speciereplacing" device; as a result, the percentage of nonactivated silver halides decreases with exposure, making the latter a decreasing function. Typical values for 77 showing this behavior are: Tri-X Pan; 6100°K, spectral region 375 to 700 m/x; HC-110, 8 min, 68°F; ij~0.1% at D = 0.10, T7~O.3% at D = 0.30, rj~0.1% at D = 1.00, and' ^ 0 . 0 0 9% at D = 2.00. For A = 466 mn (peak of P-ll phosphor), r, increases from ~ 0.09% at D = 0.10 to ~ 0.4% at D = 0.40, then decreases to ~ 0.2% at D = 1.00 and ~ 0.01% at D = 2.00
