Langmuir-Taylor detector

A Langmuir-Taylor detector (after Irving Langmuir and John Bellamy Taylor ) is a device for the detection of neutral atoms . It can therefore be used, for example, in a Stern-Gerlach experiment or to demonstrate the Lamb shift . The underlying physical effect is also called the Langmuir-Taylor effect .

functionality

The Langmuir-Taylor detector is based on the tunnel effect . For this, a is the wire of a metal with high work function (eg. B. tungsten ) is heated. If an atom comes close to this wire, the ionization energy of which is smaller than the work function of the wire material, a valence electron of this previously neutral atom can tunnel into the material with a high work function. When the wire is hot enough, the positive ions are then evaporated again from the wire and can be sucked off with an accelerating voltage. The resulting ion current is proportional to the number of incident neutral atoms. In the case of alkali atoms, almost all of the incoming atoms can be ionized.

In principle, an exchange of electrons in the direction of the arriving atom is also possible (depending on the electron affinity ), so that negative ions arise. In both cases, the proportion of ionized particles depends exponentially on the ratio of the thermal energy (with the Boltzmann constant and the thermodynamic temperature ) to the energy difference (work function vs. ionization energy ) of the two materials. In addition, effects such as possible oxidation of the wire surface must be taken into account. ${\ displaystyle k _ {\ mathrm {B}} T}$ ${\ displaystyle k _ {\ mathrm {B}}}$ ${\ displaystyle T}$

Individual evidence

^ Irving Langmuir : Thermionic Effects Caused by Vapors of Alkali Metals . In: Proceedings of the Royal Society A . 107, 1925, pp. 61-79. doi : 10.1098 / rspa.1925.0005 .
^ John Taylor: The Reflection of Beams of the Alkali Metals from Crystals . In: Physical Review . 35, No. 4, 1930, pp. 375-380. doi : 10.1103 / PhysRev.35.375 .
↑ Ingolf V. Hertel, Claus-Peter Schulz: Atoms, Molecules and Optical Physics 1 - Atomic Physics and Basics of Spectroscopy . Springer, Berlin / Heidelberg 2008, ISBN 978-3-540-30613-9 , pp. 41 .
^ Hans Pauly: Atom, Molecule and Cluster Beams I - Basic Theory, Production and Detection of Thermal Energy Beams . Springer, Berlin / Heidelberg 2000, ISBN 978-3-642-08623-6 , pp. 225 ff .

[1] Irving Langmuir : Thermionic Effects Caused by Vapors of Alkali Metals . In: Proceedings of the Royal Society A . 107, 1925, pp. 61-79. doi : 10.1098 / rspa.1925.0005 .

[2] John Taylor: The Reflection of Beams of the Alkali Metals from Crystals . In: Physical Review . 35, No. 4, 1930, pp. 375-380. doi : 10.1103 / PhysRev.35.375 .

[3] Ingolf V. Hertel, Claus-Peter Schulz: Atoms, Molecules and Optical Physics 1 - Atomic Physics and Basics of Spectroscopy . Springer, Berlin / Heidelberg 2008, ISBN 978-3-540-30613-9 , pp. 41 .

[4] Hans Pauly: Atom, Molecule and Cluster Beams I - Basic Theory, Production and Detection of Thermal Energy Beams . Springer, Berlin / Heidelberg 2000, ISBN 978-3-642-08623-6 , pp. 225 ff .