Abstract: A series of cubic AgBr core-shell emulsions were prepared from the core emulsions reduced by DMAB and shelled by AgBr.These core-shell emulsions doped with Ag₂ in the interior of grains exhibited a significant increase in sensitivity.After these emulsions were sensitized respectively by sulfur,gold or sulfur-plus-gold,the relative sensitivities of the emulsions were much higher than that of the controlled ones without Ag₂ in the interior of grains,i.e.[DMAB]=0.The results showed that a cooperative sensitization of the AgBr core-shell emulsions by internal reduction and surface chemical sensitization.On the other hand,the fog densities of these chemically sensitized emulsions rose rapidly with the amount of DMAB added in preparation of core emulsions,particularly in the cases of sulfur-plus-gold or gold sensitization.It was considered to be related to Ag₂ on the surface of grains,which were expelled from the cores in shelling process.In addition,an increase in the shelling rate was more favorable to depress the fog.

Key words: core-shell emulsion of silver bromide, chemical sensitization, cooperative sensitization