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Antimatter
Antimatter This content is archived on the CERN Document Server
In 1928, British physicist Paul Diracwrote down an equation that combined quantum theory and special relativity to describe the behaviour of an electron moving at a relativistic speed. The equation – which won Dirac the Nobel prize in 1933(link is external) – posed a problem: just as the equation x2=4 can have two possible…
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Carl D Anderson (1905-1991) discovered the positron by accident in 1932. He was photographing the tracks of cosmic rays in a cloud chamber to find the energy spectrum of secondary electrons produced by the rays. A lead plate, to slow or stop the rays divided the chamber, and a magnetic field applied to deflect the particles in different directions according to their mass. Many positive particles were observed which were too light and produced too little ionisation to be protons. Anderson concluded that they were positive electrons, or positrons.
Eighty years ago today, the journal Physical Review published a paper by physicist Carl Anderson announcing the discovery of the positron.
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