A DESCRIPTIVE THEORY OF THE PHOTO DE-ACTIVATION OF SILVER IODIDE AS AN ICE-CRYSTAL NUCLEUS

N. H. Fletcher C.S.I.R.O. Radiophysics Laboratory, Sydney, Australia

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Abstract

The photo de-activation of silver iodide as an ice-crystal nucleus is ascribed to the production of photolytic silver at trapping centers in the volume and on the surface of the nucleating particle. Silver produced at the surface raises the free energy of the interface between the nucleus and ice and so reduces the activity of the particle. The rate of de-activation is found to depend upon the size of the particle, and thus the size distribution of particles in a smoke has a strong influence upon its decay behavior. Calculations on the basis of this theory explain the wide variations in the decay rate reported in different experiments.

Abstract

The photo de-activation of silver iodide as an ice-crystal nucleus is ascribed to the production of photolytic silver at trapping centers in the volume and on the surface of the nucleating particle. Silver produced at the surface raises the free energy of the interface between the nucleus and ice and so reduces the activity of the particle. The rate of de-activation is found to depend upon the size of the particle, and thus the size distribution of particles in a smoke has a strong influence upon its decay behavior. Calculations on the basis of this theory explain the wide variations in the decay rate reported in different experiments.

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