Half a century ago the pion pioneers

Published 1997 | Version v1

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In the immediate post-World War II years, cosmic ray experiments using photographic emulsions at Bristol made historic discoveries. The picture shows Cecil Powell (standing) with M.G.K. Men on in the emulsion laboratory. md5:188280c3b556ce351157f2148d2e2626	221.4 kB	Preview Download
A classic Bristol pion. The track of the positively-charged pion produced in the interaction 'star' (top left) has been cut in two to facilitate presentation. Bottom right, the pion eventually decays into a muon, which after some 600 microns itself subsequently decays, producing an electron. This full decay chain was recorded in electron-sensitive emulsion, available from 1948, even more sensitive than the specially-developed nuclear research emulsions in which the pion was discovered in 1947. md5:7e62f935e00856a5cd1bb2ed31435fec	293.6 kB	Preview Download