Physics:Cherenkov counter
From HandWiki
Detectors for charged particles using the light emitted by Cherenkov radiation to measure the particle velocity 
. Combined with knowledge of the particle momentum, determines its mass. Cherenkov counters are therefore most commonly used as detectors for identifying particles, in conjunction with momentum measurements, e.g. in a tracking chamber (see Kleinknecht82). Their index of refraction is carefully optimized for the particle masses and momentum range of the experiment in question. Classification:
- a) Threshold counters record all light produced, thus providing a signal whenever
is above the threshold 
. - b) Differential counters accept light only in a narrow range of angles (
) i.e. in a narrow velocity interval. Resolutions of 
have been reached. As chromatic dispersion ( 
) is the major source of error at high momenta, special achromatic counters, called DISC (= directional isochronous self collimating) counters have been developed, which reach 
to 10-7. Differential Cherenkov counters suffer from the low acceptance both in angle and . - c) Ring imaging Cherenkov counters (RICH): In these detectors, particles pass through a radiator, and the radiated photons are usually focused onto a position-sensitive photon detector by a focusing device (mirror). The velocity is determined by a measurement of the radius r of the ring, on which the photons are detected. For more details,
Ring Imaging Cherenkov Counter.
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