Techniques for Processing Thick Nuclear Emulsions

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Abstract
Techniques are described for the ``eradication'' and processing of thick electron‐sensitive nuclear emulsions, and for handling ``pellicles.'' 400‐micron and 600‐micron emulsions, eradicated by a method which preserves their sensitivity to minimum‐ionization particles, exhibit marked reduction in track distortion, as well as in background. A modified procedure for uniform development of thick emulsions by the temperature‐cycling method gives a favorable ratio of grain density to background. Countermeasures against stripping of thick emulsions from their glass base have proved efficacious over a 3‐year period. A stack of emulsions without glass support (``pellicles'') provides a large sensitive volume in which tracks can be readily followed from one layer to the next. The lateral swelling (∼25 percent) during processing, which discouraged the application of this technique, was overcome by the authors [Phys. Rev. 85, 712 (1952)] in 1951. They evolved a successful method for mounting thick, stripped emulsions onto glass after exposure, but prior to processing, so that the pellicles can be developed as ordinary plates. Since then, additional experience has been gained in the application of pellicle stacks to high‐energy physics. Our procedures lead to emulsions free from lateral swelling, free from blistering, and characterized by a level of distortion sufficiently low to permit multiple scattering measurement even on fairly ``stiff'' tracks. The advantages and limitations of this technique, its possible applications, details of the mounting procedure, and methods of following tracks from layer to layer are discussed.

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