Carl David Anderson

Carl David Anderson was an American physicist who discovered the positron in 1932 and the muon in 1936. He received the 1936 Nobel Prize in Physics.

Robert Andrews Millikan: An American physicist who measured the elementary electric charge and studied cosmic rays. Millikan directed the Caltech laboratory where Anderson carried out his research.
Cloud chamber: A detector in which charged particles leave visible trails of droplets in supersaturated vapor. Anderson used cloud-chamber tracks to examine particles passing through matter.
Positron: The electron’s antiparticle, with the same mass and opposite electric charge. Anderson discovered this particle while studying cosmic-ray tracks.
Antiparticle: A particle corresponding to another particle but carrying opposite additive quantum numbers. The positron established that Dirac’s predicted antiparticles could exist in nature.
Paul Dirac: A British theoretical physicist whose relativistic equation for the electron implied the existence of antiparticles. Dirac’s theory predicted the positive electron that Anderson identified as the positron.
Wilson cloud chamber: A cloud chamber that reveals particle paths through condensation in rapidly expanded vapor. Anderson’s decisive positron evidence came from photographs made with this detector type.
Muon: An elementary particle resembling an electron but about 207 times more massive. Anderson discovered this cosmic-ray particle in 1936.
Muon problem: The historical puzzle of why a heavier particle resembling the electron exists. The muon’s discovery raised the question later captured by the phrase, “Who ordered that?”
Patrick Blackett: A British physicist who used cloud chambers to study cosmic-ray particle interactions. Blackett and Giuseppe Occhialini soon confirmed the positron through pair-production experiments.
Magnetic field: A physical field exerting forces on moving electric charges and magnetic materials. Track curvature in a magnetic field revealed particle momentum and charge sign.

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