Low-intensity reciprocity failure (LIRF) of a silver bromide emulsion was drastically reduced, but not eliminated, by the addition of a halogen acceptor, such as acetone semicarbazone, before coating. The remaining failure has a slope of approximately minus unity on an isodensity plot of log intensity vs log intensity × time. This is interpreted as exemplifying two types of LIRF, an intergranular type stopped by a sufficient amount of halogen acceptor, and an intragranular type caused by the thermal instability of a photolytically produced silver atom. A LIRF curve was also obtained in terms of the number of absorbed photons necessary to make a grain developable. These data suggest that considerable recombination occurs before nucleation of the latent image. The quantum efficiency of formation of print-out silver is 0.2 silver atom per absorbed photon. This value indicates that growth of the latent image after nucleation is efficient.
H. E. SPENCER and D. H. SHARES, "Low-Intensity Reciprocity Failure of a AgBr Emulsion: Effect of Halogen Acceptors," J. Opt. Soc. Am. 57, 508-512 (1967)