Cosmic-ray work with emulsions in the 1940s and 1950s

This chapter considers technical advances made in the 1940s and 1950s in the production of photographic emulsions for use in detecting and studying cosmic rays. The discovery, of the pion predicted theoretically by Yukawa in 1947 is described, and the dependance of its discovery on the new sensitive emulsions noted. The paper also charts work by physicists in a number of countries on kaons, the other intermediate mass particles discovered at this time. Later technical advances included thicker emulsions (up to 1,000 μm) and very large polyethylene balloons to take experimental apparatus up into the high cosmic-ray intensity stratosphere. Many of the balloon experiments were international collaborations. (UK)