Isothermal Processing of Thick Nuclear Emulsions

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Abstract
A method for the processing of thick nuclear emulsions is outlined which develops the tracks of singly charged particles at the minimum of ionization without resort to a hot stage. The developing agent is introduced into the thick layer by means of a series of solutions varying in pH from 4.7 to 7.2 and of increasing reducing power. Uniform depth development is secured by allowing the last solution to diffuse out of the emulsion into water at 5°C. The processes of fixation and washing are designed to avoid resolution of surface silver grains, and to keep lateral swelling at a minimum. Turbidity resulting from residual silver iodide is reduced by means of a buffered thiourea solution. Thick unsupported emulsions can be restored to approximately their original size by leaching the electrolytes from the gelatin with a series of graded alcohols. The isothermal cold processing reduces distortion and facilitates the microscopic study of preparations up to 2 mm thickness by minimizing danger of overdevelopment and production of excessive fog.