Comparative Study of the Sensitivity Specks Formed During the Ripening of Silver Chloride Relative to Silver Bromide with Gold-198 and Gold-198 Plus Sulphur-35^*

* This work was supported by the IWONL (Insliluut voor Wetenschappelijk Onderzoek in Nijverheid cn Landbouw) of Belgium.

^†

† Extended version of a poster presented during the ICPS Congress at Cologne, 10-17 Sept. 1986.

Abstract

By means of radioactive tracers ³⁵S and ¹⁹⁸Au a comparative study of the composition of the sensitivity specks formed during the ripening of silver chloride and silver bromide emulsions with equal grain size (a = 0.2 //m) was made and related to their photographic response. The sensitizers used were gold chloride (¹⁹⁸Au) and gold chloride combined with sodium thiosulphate (³⁵S_ext).

A washing technique was required to differentiate between gold in a more or less soluble state adsorbed on the emulsion grains during ripening. A 10^{-4 M} sodium sulphite solution was found to be useful. This gold-complexing solution was able to desorb gold ions from the grain surface, leaving undesorbed the presumed gold sulphide, silver gold sulphide, gold or gold oxide specks.

The following conclusions could be drawn:

(1) The ripening of silver chloride and silver bromide emulsions with gold chloride results in the formation of identical amounts of non-desorbable gold, but corresponding with higher fog values for the AgCI emulsions.

(2) The ripening with gold thiosulphate results in non-desorbablc gold amounts which are more important in the case of silver bromide than of silver chloride, and this again with higher fog values for silver chloride. This supports an earlier hypothesis that gold ions have a stronger activity to reduce the sensitized silver chloride grains than sensitized silver bromide grains.

During the ripening with gold thiosulphate the molar ratio S/Au at optimum sensitivity seems to be of the same order of magnitude (3.5) for AgBr and AgCI, and leads to a formula of Ag₁₂Au₂S₇ for the sensitivity speck.

Notes

* This work was supported by the IWONL (Insliluut voor Wetenschappelijk Onderzoek in Nijverheid cn Landbouw) of Belgium.

† Extended version of a poster presented during the ICPS Congress at Cologne, 10-17 Sept. 1986.