Editing Geiger–Müller tube (section)

==Types of tube==
Broadly, there are two important types of Geiger tube construction.

===End window type===
[[File:Geiger-Muller-counter-en.png|thumb|Schematic of a Geiger counter using an "end window" tube for low-penetrating radiation. A loudspeaker is also used for indication]]
For alpha particles, low energy beta particles, and low energy X-rays, the usual form is a cylindrical '''end-window tube'''. This type has a window at one end covered in a thin material through which low-penetrating radiation can easily pass. [[Mica]] is a commonly used material due to its low mass per unit area. The other end houses the electrical connection to the anode.

====Pancake tube====
[[File:Geiger tube si8b.jpg|thumb|right|Pancake G–M tube, the circular concentric anode can clearly be seen.]] 
The '''pancake tube''' is a variant of the end window tube, but which is designed for use for beta and gamma contamination monitoring. It has roughly the same sensitivity to particles as the end window type, but has a flat annular shape so the largest window area can be utilized with a minimum of gas space. Like the cylindrical end window tube, mica is a commonly used window material due to its low mass per unit area. The anode is normally multi-wired in concentric circles so it extends fully throughout the gas space.

===Windowless type===
This general type is distinct from the dedicated end window type, but has two main sub-types, which use different radiation interaction mechanisms to obtain a count.

====Thick walled====
[[File:GM tubes.jpg|thumb|A selection of thick walled stainless steel G–M tubes for gamma detection. The largest has an energy compensation ring; the others are not energy compensated]]
Used for gamma radiation detection above energies of about 25 KeV, this type generally has an overall wall thickness of about 1-2{{Spaces}}mm of [[Low-background steel|chrome steel]]. Because most high energy gamma photons will pass through the low density fill gas without interacting, the tube uses the interaction of photons on the molecules of the wall material to produce high energy secondary electrons within the wall. Some of these electrons are produced close enough to the inner wall of the tube to escape into the fill gas. As soon as this happens the electron drifts to the anode and an electron avalanche occurs as though the free electron had been created within the gas.<ref name="knoll"/> The avalanche is a secondary effect of a process that starts within the tube wall with the production of electrons that migrate to the inner surface of the tube wall, and then enter the fill gas. This effect is considerably attenuated at low energies below about 20 KeV <ref name="centronics"/>

====Thin walled====
Thin walled tubes are used for:
* High energy beta detection, where the beta enters via the side of the tube and interacts directly with the gas, but the radiation has to be energetic enough to penetrate the tube wall. Low energy beta, which would penetrate an end window, would be stopped by the tube wall. 
* Low energy gamma and X-ray detection. The lower energy photons interact better with the fill gas so this design concentrates on increasing the volume of the fill gas by using a long thin walled tube and does not use the interaction of photons in the tube wall. The transition from thin walled to thick walled design takes place at the 300–400 keV energy levels. Above these levels thick walled designs are used, and beneath these levels the direct gas ionization effect is predominant.

===Neutron detection===
{{main|Neutron detection}}
G–M tubes will not detect [[neutron]]s since these do not ionize the gas.  However, neutron-sensitive tubes can be produced which either have the inside of the tube coated with [[boron]], or the tube contains [[boron trifluoride]] or [[helium-3]] as the fill gas, or the tube is wrapped in about {{cvt|0.5|mm|in|frac=50}} thick [[cadmium]] foil.<ref>{{Cite web |url=https://frank.pocnet.net/sheets/030/1/18503.pdf |title=Philips 18503 datasheet |access-date=2022-01-03 |archive-date=2022-01-03 |archive-url=https://web.archive.org/web/20220103011420/http://www.frank.mif.pg.gda.pl/sheets/030/1/18503.pdf |url-status=live }}</ref> The neutrons interact with the boron nuclei, producing alpha particles, or directly with the helium-3 nuclei producing hydrogen and [[tritium]] ions and electrons, or with the cadmium, producing gamma rays.  These energetic particles interact and produce ions that then trigger the normal avalanche process.