The relationship between mass, m, velocity, v, and wavelength, , is known as the de Broglie relationship, after the man who first proposed it on theoretical grounds three years before the Davisson-Germer experiment.

This relationship is = h/mv in which h is Planck's constant, the same constant we encountered previously in the photoelectric effect. Since both mass and speed are in the denominator of the expression, we can see that a heavy particle or a rapidly moving one will have a short wavelength.

The de Broglie wavelength relationship does not apply only to electrons. It is valid for every particle in the universe, but the only particles that have small enough mass that their wavelengths are long enough to detect are electrons, protons, and neutrons.

In addition to x-ray and electron diffraction, neutron diffraction is one of the standard tools of molecular structure analysis today.