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The Discovery of the Positron

American physicist Carl Anderson was using a cloud chamber to examine trails left by cosmic rays.He put a lead plate in the chamber to see if the particles would pass through and be slowed down when they passed through the plate.He discovered a beta particle that slowed down but was deflected in the opposite direction to all the other beta trails.This positron was the first antiparticle to be detected.

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Specification: AQA Physics (7407), AS-level, 3.2.1.3 Particles, antiparticles and photons and 3.2.1.5 Classification of particles. Topic: Particles and Radiation.

Key terms in this lesson

Hadron
A particle made up of quarks that interacts through the strong interaction; hadrons are divided into baryons and mesons.
Baryon
A hadron made of three quarks, for example the proton and the neutron.
Meson
A hadron made of a quark-antiquark pair, for example the pion and the kaon.

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