Delbrück scattering
deflection of high-energy photons in the Coulomb field of nuclei as a consequence of vacuum polarization
Delbrück scattering, the deflection of high-energy photons in the Coulomb field of nuclei as a consequence of vacuum polarization, was observed in 1975. The related process of the scattering of light by light, also a consequence of vacuum polarization, was not observed until 1998. In both cases, it is a process described by quantum electrodynamics.
Discovery
From 1932 to 1937, Max Delbrück worked in Berlin as an assistant to Lise Meitner, who was collaborating with Otto Hahn on the results of irradiating uranium with neutrons. During this period he wrote a few papers, one of which turned out to be an important contribution on the scattering of gamma rays by a Coulomb field due to polarization of the vacuum produced by that field (1933). His conclusion proved to be theoretically sound but inapplicable to the case in point, but 20 years later Hans Bethe confirmed the phenomenon and named it "Delbrück scattering".
In 1953, Robert Wilson observed Delbrück scattering of 1.33 MeV gamma-rays by the electric fields of lead nuclei.
Description
Delbrück scattering is the coherent elastic scattering of photons in the Coulomb field of heavy nuclei. It is one of the two nonlinear effects of quantum electrodynamics (QED) in the Coulomb field investigated experimentally. The other is the splitting of a photon into two photons.
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