Processing Thick Emulsions for Nuclear Research

Abstract

IN the application of the photographic method to research in cosmic-ray and nuclear physics, the need has always been felt for emulsions of thickness comparable with the range of the particles to be recorded. The use of thick emulsions has been greatly restricted, however, by the difficulties met in processing them. It has been possible to use plates with emulsions 200µ thick but, using conventional methods, the degree of development is found to be much greater at the top than at the bottom of the emulsion. It follows that the grain density, in the tracks of particles of the same ionizing power, varies with the depth of the track ; a result which leads to great difficulty in interpreting the experimental material even in experiments where it is possible to use short exposures so that complications due to fading are not present. We give here a brief outline of a method of processing which has enabled us to produce a nearly uniform development of emulsions 300µ thick, so that the grain density in the tracks of particles in regions of equal ionization does not vary by more than 10 per cent from the top to the bottom of the emulsion.