C.T.R. Wilson

Charles Wilson is 2nd from right in the front row. Can you find Paul Langevin and O.W. Richardson?

First cloud chamber “the most original and wonderful instrument in scientific history.” - Rutherford

Diagram

ALPHA broad, straight track BETA thin, bending track GAMMA no tracks as too few ions are produced in the air

1911 photo

1912 photo 1912 Wilson photo

Compton Scattering : What? X-ray photons collide with electrons in carbon atoms. The scattered photons are shifted to longer wavelengths (lower energies).

Compton Scattering : So What? The particle theory of light was still controversial in the 1920’s, despite Einstein’s photoelectric effect. Compton used a particle model of the photon, and classical conservation of momentum, to explain the shift in wavelength of the observed scattered x-rays.

evidence of Compton Effect (Nobel Prize Compton & Wilson 1927) evidence of transmutation of elements (Rutherford’s N +  -> O + p) discovery of positron and the pair creation- annihilation of electrons & positrons (Nobel Prize Anderson 1936) discovery of muon

P. BLACKETT “counter controlled cloud chamber” (Nobel Prize 1948) added a Geiger Counter above & below the c.c. Cosmic rays triggered gas expansion and their own photos when impulses hit both counters simultaneously. D.A. GLASER “bubble chamber” replaced the c.c. in 1952, using liquid He or H 2. Higher density medium allowed photos of high-E particles that were too fast for the c.c. Beyond the Cloud Chamber

Web Resources how to make a cloud chamberhttp://home.houston.rr.com/molerat/cloud.htm ss.html Wilson’s Nobel addresshttp:// ss.html astr.gsu.edu/hbase/quantum/comptint.html#c1 Compton Effecthttp://hyperphysics.phy- astr.gsu.edu/hbase/quantum/comptint.html#c1 ng_physics.htm lightning physicshttp:// ng_physics.htm