Results of the authors' experiments on the print-out effect of a silverc hloride emulsion are summarized, and a quantitative interpretation of this effect is given. The quantum yield of silver production became unity only when low-pAg emulsions were given small exposures at low intensities. The yield usually decreased with increasing intensity. Print-out silver separated preferentially on the surface of silver chloride grains when low-pAg emulsions were given small exposures. Internal printout silver appeared with large exposures or with high-pAg emulsions. From these data it was concluded that excess silver ions in gelatin in low-pAg emulsions play the role of a source of silver ions for the neutralization of photoelectrons as well as the role of traps for photoelectrons. The intensity-dependent quantum yield φ may be expressed by the following equation
φ=
cv/
m0(1+ln
m0/
cv)
-e-sd/1-e-εd,
where
c is the number of electron traps at the surface of silver chloride per unit volume of the emulsion,
v is the number of silver ions arriving at an electron trap per unit time,
m0 is a constant proportional to intensity, ε is the “absorption coefficient” of the emulsion layer, and
d is the thickness of the emulsion layer. With this equation the value of
cv was calculated to be of the order of 10
15cm
-3. sec
-1. Trials for independent determinations of
c and
v respectively are also described.
c was determined by measuring the size of print-out silver particles with the aid of their color.
v was determined by measuring the electrical conductivity of silver ions in gelatin film. The values thus obtained are consistent with the value of
cv calculated above.
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