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Here, Δλ denotes the difference between the wavelengths of the incoming and the scattered ray, while θ is the angle of scattering.
Here, Δλ denotes the difference between the wavelengths of the incoming and the scattered ray, while θ is the angle of scattering.
== The Compton Experiment ==
A collimated beam of high-energy photons, e.g. emitted from a radioactive <sup><small>137</small></sup>Cs source or an X-ray emitter hits a target, e.g. a rod of graphite. A [[scintillation counter]] is used to measure the number and the energy of the deflected photons at various angles.
== Classical Expectation ==
The number of photons should vary with the angle of the deflection, while the energy (i.e., the wavelength) of the photons should remain unchanged.
== Observation ==
While indeed many of the scattered photons have an unchanged wavelength, there are some which lost energy, i.e., their wavelength lengthened. This lengthening depends on the angle of the deflection only.
The probability for Compton scattering is approximately proportional to the [[atomic number]] Z, and for energies greater than 500 [[keV]] approximately proportional to <math>\frac{1}{E^\gamma}</math>,<ref>{{cite web|url=http://ie.lbl.gov/education/glossary/glossaryf.htm|title=Glossary of Nuclear Science Terms|accessdate=January 10, 2013}}</ref> the energy of the [[gamma ray]] [[photon]].
The probability for Compton scattering is approximately proportional to the [[atomic number]] Z, and for energies greater than 500 [[keV]] approximately proportional to <math>\frac{1}{E^\gamma}</math>,<ref>{{cite web|url=http://ie.lbl.gov/education/glossary/glossaryf.htm|title=Glossary of Nuclear Science Terms|accessdate=January 10, 2013}}</ref> the energy of the [[gamma ray]] [[photon]].