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Elementary Particles

History

synchrocyclotron, cloud chamber, ocean tides, gravitational attraction, cosmic rays

Deeper web pages:

>  Identifying Parts of the Atom

>  Pauli and Neutrinos

>  Discovery of Antimatter

>  Search for Carriers of the Strong Force

>  Invention of the Cyclotron

>  Separating Leptons and Quarks

>  The Standard Model

In 1931 British physicist Paul Dirac produced the precursor of modern particle theories. Dirac’s equations described the known electromagnetic properties of particles well, but to make his theory work more comprehensively, Dirac had to introduce the idea of antiparticles, antimatter counterparts of existing particles. The existence of these particles was confirmed in 1933, when American physicist Carl Anderson saw something peculiar while looking at tracks made by cosmic rays in a type of particle detector called a cloud chamber. A particle passing through the cloud chamber seemed to have the mass of an electron, but it had a positive rather than a negative charge—he had discovered the positron. Anderson shared the 1936 Nobel Prize in physics for this confirmation of Dirac’s theory.

Einstein and Particles of Light

While cosmic ray experiments revealed a myriad of particles, scientists also sought ways to create unusual and unstable particles in laboratories. American physicist Ernest Lawrence invented the cyclotron, a type of circular accelerator, in 1932. The cyclotron, however, could not achieve very high energies. Lawrence’s model was improved (independently) by American physicist Edwin McMillan and Soviet physicist Vladimir Veksler in the 1940s, resulting in the synchrocyclotron. The high energies available using the synchrocyclotron led to many important particle discoveries.

A Third Generation of Particles

Gravitation plays a crucial role in most processes on the earth. The ocean tides are caused by the gravitational attraction of the moon and the sun on the earth and its oceans. Gravitation drives weather patterns by making cold air sink and displace less dense warm air, forcing the warm air to rise. The gravitational pull of the earth on all objects holds the objects to the surface of the earth. Without it, the spin of the earth would send them floating off into space.

The gravitational attraction of every bit of matter in the earth for every other bit of matter amounts to an inward pull that holds the earth together against the pressure forces tending to push it outward. Similarly, the inward pull of gravitation holds stars together. When a star's fuel nears depletion, the processes producing the outward pressure weaken and the inward pull of gravitation eventually compresses the star to a very compact size.



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