The atomic structure [4]: Wave-particle duality

In 1922 Compton began to study electromagnetic waves, with special interest on the interaction between X rays and a graphite target. He observed that a radiation was emitted, and its wavelength was higher than the incident one. This phenomena couldn't be explained by classical theories. They expected that the emitted radiation was characterized by the same frequency of the incident one, because it was supposed to make graphite particle oscillate with its frequency.

 Compton proposed that this phenomena could be explained as an interaction between particles: photons and electrons. Photons, interacting with graphite, are going to hit electrons, shifting part of they energy. The electron is therefore going to be emitted with a lower kinetic energy than the photon. It means that also the frequency will be lower, thus the wavelength will be higher, explaining the Compton scattering.


This new discovery, together with photoelectric effect, showed that light behaved ad a particle. De Broglie, was firmly convinced about unity in nature: if waves behaved like matter, also matter had to behave like waves. In 1924 he proposed that the motion of particles was related to the propagation of a certain wave, according to his hypothesis:

This was experimentally proved in 1927 by Davidson and Germer. For instance if an electromagnetic wave is forced to pass through a hole with radius comparable to it's wavelenght, it will create diffraction. The same behavior is observed if electrons are forced to pass through a hole of radius comparable to their de broglie-wavelength, confirming wave particle duality of light and matter.