Detection of Radiation
Devices
Individual particles such as electrons, neutrons, and protons cannot be seen directly, so their existence must be inferred through measurements.
Many different devices, of varying levels of sophistication, have been developed to do this.
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Geiger Counter The Geiger counter is a gas-filled tube with a wire in the center. The wire is at high voltage; the case is grounded. When a charged particle passes through, it ionizes the gas. The ions cascade onto the wire, producing a pulse Scintillation Counter
A scintillation counter uses a scintillator – a material that emits light when a charged particle goes through it.
The scintillator is made light-tight, and the light flashes are viewed with a photomultiplier tube, which has a photocathode that emits an electron when struck by a photon and then a series of amplifiers.
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| Geiger Counter | Scintillation Counter |
| Cloud Chamber A cloud chamber contains a supercooled gas
When a charged particle goes through, droplets form along its track.
Similarly, a bubble chamber contains a superheated liquid, and it is bubbles that form. In either case, the tracks can be photographed and measured. Wire Chamber A wire drift chamber is somewhat similar to, but vastly more sophisticated than, a Geiger counter.
Many wires are present, some at high voltage and some grounded.
in addition to the presence of a signal, the time it takes the pulse to arrive at the wire is measured, allowing very precise measurement of position. |
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| Cloud or Bubble Chamber | Wire chamber |
Pictures (in progress)
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| Geiger Counter | Wire Chamber | Bubble Chamber |