SCIENCE WATCH

The Positive Electron: 88 years ago Carl Anderson's discovery of the positron was published #OnThisDay in 1933.

In developing quantum mechanical theory, Paul Dirac predicted that all matter has a kind of mirror image - antimatter. A particle and its antiparticle, if charged, should have opposite charges. By studying the tracks of cosmic ray particles in a cloud chamber, Anderson discovered a positively-charged particle with a mass seemingly equal to that of an electron, in 1932, Anderson's particle was the first antiparticle proven by experiment and was named a "positron".

Anderson was awarded the Nobel Prize in Physics in 1936.

Image: Cloud chamber photograph by Anderson, the first positron ever observed. A 6 mm lead plate separates the upper and lower halves of the chamber. The deflection and direction of the particle's ion trail indicate the particle is a positron.

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