C.T.R. Wilson

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

Nobel Prizewith Compton

1927

2 major paperswith illustrationspublished 1923

first photos ofα,β particles

1911

first chamber- x ray photos

1895

Cloud Chamber

" published Theory of "Thundercloud Electricity

1956

promoted to Reader of Electrical Meteorology

1918

. Observer in Met Physics Solar Physics Observatory

1913appointed

Meteorological Societyemployment

1899

AtmosphericElectricity

MAJOR INTERESTS

“the most original and wonderful instrument in scientific history.”

- Rutherford

• ALPHA broad, straight track

• BETA thin, bending track

• GAMMA no tracks as too few ions are

produced in the air

1911 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).

incoming

photon λiscattered

photonλse- at reste-

recoil

angleθ

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.

Δλ = hmec(1-cosθ)

• evidence of Compton Effect (Nobel Prize Compton & Wilson 1927)

• evidence of transmutation of elements (Rutherford’s N + α -> 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 H2. Higher density medium allowed photos of high-E particles that were too fast for the c.c.

Beyond the Cloud Chamber

Web Resources

• http://home.houston.rr.com/molerat/cloud.htm how to make a cloud chamber

• http://www.nobel.se/physics/laureates/1948/press.html Wilson’s Nobel address

• http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/comptint.html#c1 Compton Effect

• http://www.boltlightningprotection.com/lightning_physics.htm lightning physics