The simultaneity in the Compton effect has been investigated by using scintillation counters and fast coincidence techniques. By the use of a gamma-ray source of a known, very short, lifetime (${\mathrm{Ni}}^{60}$) it was possible to apply a first moment investigation to the time delays involved.

It is shown that the order of magnitude of all possible time delays involved in the Compton effect does not exceed ${10}^{-11\mathrm{}}$ second. Upper limits previously given were ∼${10}^{-8\mathrm{}}$ second.

• Received 22 October 1954

DOI:https://doi.org/10.1103/PhysRev.97.1710