Ramsauer–Townsend effect

The effect is named for Carl Ramsauer and John Sealy Townsend, who each independently studied the collisions between atoms and low-energy electrons in 1921.

Because noble gas atoms have a relatively high first ionization energy and the electrons do not carry enough energy to cause excited electronic states, ionization and excitation of the atom are unlikely, and the probability of elastic scattering over all angles is approximately equal to the probability of collision.

[5] No good explanation for the phenomenon existed until the introduction of quantum mechanics, which explains that the effect results from the wave-like properties of the electron.

Niels Bohr presented a simple model for the phenomenon that considers the atom as a finite square potential well.

[6][7] Predicting from theory the kinetic energy that will produce a Ramsauer–Townsend minimum is quite complicated since the problem involves understanding the wave nature of particles.

Above, an atom is represented by a yellow disk. The classical trajectory of an electron is modelled in black. Below, a graph that sketches the relation between current and voltage across a noble gas. The current does not increase monotonically when the voltage increases.