Positron Track from a Cloud Chamber

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© Positron Track: Lawrence Berkeley National Laboratory. Portraits: Wikimedia Commons, Public Domain.

The first sight of antimatter came in a particle track observed in a cloud chamber at the California Institute of Technology by physicist Carl Anderson in 1932. The track curved in the opposite way from the track of an electron, showing that the particle had a positive charge. But the track was too faint to come from a positively-charged proton. Anderson had discovered the positively-charged electron, or positron, predicted by Paul Dirac in 1929. Cosmic rays continued to provide important data on high-energy particles. (Unit: 1)