In Leeds we use two kinds of detectors:
The scintillator detector is made up of a special piece of plastic called a `scintillator'. When fast moving, charged particles, such as cosmic rays pass through the scintillator they excite the atoms in the plastic by giving them some energy (the cosmic ray then slows down a little). The excited atoms then lose this energy by emitting some photons of light. The light is detected by a sensitive piece of equipment called a "photomultiplier".
The photomultiplier, as its name suggests, multiplies
the small flash of light into a large electrical signal that can be
measured. From the size of the electronic signal we can tell how many
particles passed through the scintillator. The scintillator and the
photomultiplier are housed in a dark box so that the only light detected
is caused by cosmic rays. This kind of detector is illustrated in the
diagram below. These kind of detectors are used in the
SPASE-2 array.
Water Cerenkov detectors are similar to the scintillator detectors except that
the dark box contains no scintillator but is filled with pure, clear water.
When cosmic rays pass through the water they emit faint flashes of blue light
known as Cerenkov radiation. The sides of the water
tank are lined with reflective material and some of this light is reflected
onto a photomultiplier which produces an electronic signal. The size of the
signal can be used to find out how many cosmic rays passed through the
detector. This kind of detector was used in the 12 square kilometre array
at Haverah Park. A diagram of this kind of detector
is shown below.
