Ramsauer–Townsend effect

The Ramsauer effect, also known as the Ramsauer - Townsend effect, refers to the extreme permeability of gases compared with slow electrons and was discovered by Carl Ramsauer 1920. He is now regarded as the first experimental evidence that electrons can not be written with classical mechanics.

When electrons pass through a gas, they interact with the gas molecules interact. To determine this interaction Ramsauer introduced the term cross-section, the greater is the cross section of a gas molecule, the more likely it is struck by an electron, and the less electron- permeate gas. According to the ideas of classical mechanics, the cross section should be smaller, the greater the kinetic energy and thus the speed of the electron is because slower electrons would strongly deflected by the electric field inside the atoms.

Ramsauer noted, however, that the cross section strongly depends on the kinetic energy of the electrons. So in about one electron volt show many cross-sections at a minimum, which is partially well below the gas- kinetic cross section. With increasing electron energy of the collision cross section first increases to a maximum and then decrease again sharply at values ​​above 20 eV, partially below the value of the minimum collision cross section at lower energies ( Ramsauer cross section). The minimum of the cross section can be heuristically by the wave -particle duality explain: The dependent on the speed of de Broglie wavelength of the electrons must move in the same order of magnitude as the size of the scattering of the electrons causing gas atoms. Thus, the gas atoms allow the transmission of the electrons, so electrons of a certain wavelength can pass through the gas molecules freely. The full explanation of this effect by means of quantum mechanical scattering theory. By the wave nature of the electrons occurs due to the transmission behind the atoms to interference phenomena, which are not objects of observation are.

Although this effect was not explained at the time, Ramsauer presented its results on September 7, 1920 for publication in the Annals of Physics. Only with de Broglie's theory of matter waves of the Ramsauer effect was first understood heuristically. His full explanation required the developed 1925-1927 quantum mechanics.

The name also used for this effect Ramsauer - Townsend effect includes the research of the Irish physicist John Sealy Edward Townsend, who in 1901 discovered the dependence of the mean free path of the kinetic energy in the motion of free electrons in gases.

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