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→Introduction: added figure "Dominant Photon-Matter Interaction"
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== Introduction ==
[[File:Compton-en.svg|thumb|right|Fig. 1: Schematic diagram of Compton's experiment. Compton scattering occurs in the [[graphite]] target on the left. The slit passes X-ray photons scattered at
[[File:Dominant Photon-Matter Interaction.svg|thumb|Plot of photon energies calculated for a given element (atomic number Z) at which the [[Cross section (physics)|cross section]] value for the process on the right becomes larger than the cross section for the process on the left. For calcium (Z=20), Compton scattering starts to dominate at ''hυ''=0.08 MeV and ceases at 12 MeV.<ref>{{Cite journal |date=2009-09-17 |title=XCOM: Photon Cross Sections Database |url=https://dx.doi.org/10.18434/T48G6X |journal=NIST |doi=10.18434/T48G6X |language=en |last1=Seltzer |first1=Stephen }}</ref>]]
In Compton's original experiment (see Fig. 1), the energy of the X ray photon (≈17 keV) was significantly larger than the binding energy of the atomic electron, so the electrons could be treated as being free after scattering. The amount by which the light's wavelength changes is called the '''Compton shift'''. Although nucleus Compton scattering exists,<ref>{{cite journal|title=Nuclear Compton scattering|author=P. Christillin|year=1986|journal= J. Phys. G: Nucl. Phys.|volume=12|pages=837–851|url=https://iopscience.iop.org/article/10.1088/0305-4616/12/9/008/meta|doi=10.1088/0305-4616/12/9/008|bibcode = 1986JPhG...12..837C|issue=9 |s2cid=250783416 }}</ref> Compton scattering usually refers to the interaction involving only the electrons of an atom. The Compton effect was observed by [[Arthur Holly Compton]] in 1923 at [[Washington University in St. Louis]] and further verified by his graduate student [[Wu Youxun|Y. H. Woo]] in the years following. Compton was awarded the 1927 [[Nobel Prize in Physics]] for the discovery.
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