Nuclear Emulsions

Nuclear Emulsion Cosmic Ray Experiment

                         Contributed by Colin Gauld.

The Nuclear Emulsion Group operated under the leadership of Brian McCusker, Frankie Brisbout and Freddie Herz (and, for a short time, K Nishikawa), along with scanners Rosemary Roberts, Dindy Vaughan, Gloria Twynham and Wendy Barton and research students Laurie Peak, Bert van Loon, Tony Gray, Graham Day, Elizabeth Farrow and me. The programme focussed on collisions between cosmic ray particles and the nuclei in a stack of thick sheets of photographic emulsion which became visible when the emulsion sheets were developed. When I began in 1960 we were commencing an involvement in an international collaboration in which the sheets in an 80 litre stack had been divided between participating groups for analysis. The first paper from the international collaboration (ICEF) had 99 authors! In one experiment which we carried out alone Teflon sheets were placed between the layers of emulsion to simulate the collisions which took place in the atmosphere.

The photographs show the way in which the emulsion stacks were exposed to the cosmic ray particles before they had interacted in any major way with the atmosphere. This was in New Mesico around 1962. The stack was placed inside a Styrofoam container to protect it when it landed and connected to the bottom of the deflated balloon. The point of connection was attached to a crane which was on the back of a truck. The balloon was filled with helium but was held down by a restraining bar. When the bar was released the truck attempted to remain below the ascending balloon until it was vertical at which time the restraining bar was removed, the load was disconnected from the crane and the balloon rose to a height of around 30,000 metre.

At the end of the flight the load was cut free of the balloon and parachuted to earth where it was collected and separated into its individual sheets. These were developed using the processing equipment in the Ryerson Physics Laboratory at the University of Chicago under the eagle eyes of Dave Haskin and Jorge Barault.

The scanners then analysed the tracks going into and out of the collision to determine their density and angle. From this information the nature of the particles and their properties could be determined.


Some photographs of a balloon launch in New Mexico in about 1961 or 1962: