The tracks of the Compton effect.
The observation of scattered radiations of larger wavelength than the primary had been repeatedly rejected or explained away by many researchers, including Compton. After years of vacillations, he recognized the effect named after him and was the first to develop a quantal equation predicting the wavelength of scattered radiation. It became one of the most significant contributions to modern radiation physics, opening the doors of quantum mechanics.
D049672:History, 19th Century; D049673:History, 20th Century; D011871:Radiology / Q000266:history*; D012542:Scattering, Radiation; D014481:United States