HEGRA pictures

HEGRA detectors

Scintillator detectors:

These kind of detectors are mostly used in Nuclear and Particle Physics. They're based on materials that have the property of emitting light when being reached by a particle ( specially when it's a charged one ). This light is detected by one or more photomultipliers which turn them into an electric pulse. This pulse is subsequently electonically analyzed in order to get information about the incident particle (arrival time, energy...). HEGRA experiment scintillator detectors are installed in one meter height huts (see picture). They are used to detect the shower charged particles ( mostly electrons). The different arrival times of particles to each one of the huts allow us to reconstruct the primary cosmic ray direction.

Cherenkov light (huts):

When a charged particle moves across a material medium faster than the speed of light in this medium it emits waves ( Cherenkov light ), in some way similar to the sound shock waves produced by supersonic airplanes. Shower electrons and positrons can emit this kind of radiation, which we are able to detect using photomultipliers (see scheme) on clear no mooned nights (moonlight or sunlight would burn these photomultipliers). This reduces observation time but allows us a more precise determination of the shower incident direction.

Cherenkov Telescopes (Small one & Big one):

Cherenkov radiation can be also detected with special telescopes, that basically work like optical telescopes (at least in what refers to focusing light), though not having as good resolution. The Cherenkov light produced in air showers generated by cosmic rays coming from the direction the telescope is pointing at is collected by a set of mirrors which reflect it towards an array of photomultipliers which is held in front of them by three or four masts (see pictures).

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