Delbrück scattering, the deflection of high-energy photons in the Coulomb field of nuclei as a consequence of vacuum polarization, was observed in 1975.
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.
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".
[3] Delbrück's arguments were based on the relativistic quantum mechanics of Dirac according to which the QED vacuum is filled with electrons of negative energy or – in modern terms – with electron-positron pairs.
This experiment was the first where exact predictions based on Feynman diagrams,[13][14][15] were confirmed with high precision and, therefore, has to be considered as the first definite observation of Delbrück scattering.
[16][17] Nowadays, the most accurate measurements of high-energy Delbrück scattering are performed at the Budker Institute of Nuclear Physics (BINP) in Novosibirsk (Russia).
In general, in the low energy nuclear physics region i.e. <10–20 MeV, a Delbrück experiment measures a number of competing coherent processes including also Rayleigh scattering from electrons, Thomson scattering from the point nucleus and nuclear excitation via the giant dipole resonance.