In 1924, physicists Walther Bothe and Hans Geiger used the coincidence method to probe the Compton scattering of gamma rays and x-rays, a phenomenon whose quantum mechanical nature (see particle-wave duality) with regard to energy conservation was ambiguous at the time. The Bothe–Geiger experiment was the first significant coincidence experiment to test the transfer of energy between the incoming photon and the electron in this process. The experiment utilized two Geiger counters: one to detect the initial recoiling election and one to simultaneously detect a secondary electron recoil caused by the photonic product of the first recoil. This setup included a coincidence circuit which measured the process to τ τ = 1 ms and with an accuracy of 0.1 ms. In 1954, Bothe won the Nobel Prize in Physics for this work.