Cosmic rays are currently detected by...scintillation detectors, Cerenkov radiation detectors, and photodiodes that measure flourescent light in the sky on moonless, cloudless nights (d).
Scintillation detectors (a) are made up of a scintillating material, which is attached to a photomultiplier tube. The scintillating material scintillates (i.e. emits light) when a charged particle passes through it. The photomultiplier detects the light signal, amplifies it, and converts it into an electrical pulse. These electrical pulses can be used to determine the energy of the particles passing through the detector. With a large array of detectors, one can work backwards to determine the energy of the original cosmic ray. A schematic of a scintillation detector is shown below.
Cerenkov radiation detectors (b) are water tanks with photomultiplier tubes surrounding the tanks. Einstein's theory of special relativity states that nothing can travel faster than the speed of light in a vacuum. However, in a medium such as water, light is slowed down, while other particles, such as muons and neutrinos, are not. When a particle travels faster than light travels in a given medium, it emits light. This light is known as Cerenkov radiation, analogous to the sonic boom one experiences when traveling faster than the speed of sound. The photomultiplier tubes detect the Cerenkov radiation and the energies of the particles can then be deduced. A schematic of a water Cerenkov detector is shown below.
Photodiodes that measure flourescent light in the sky on moonless, cloudless nights (c) are also used to detect cosmic rays. Electrons and positrons produced in cosmic ray showers collide with gas molecules in the atmosphere, and excite electrons within these gas molecules to higher energy states. When the electrons within these gas molecules return to the ground energy state, they emit radiation. Nitrogen is the most abundant element in the earth's atmosphere and thus, most of the radiation emitted in these processes is from nitrogen. Photodiodes are tuned to a specific frequency range and pointed towards a region of the sky. When they detect radiation, they emit an electrical pulse, which can be analyzed. The advantage of this method is that with an array of photodiodes, you can see a cosmic ray air shower develop as it passes through the atmosphere. However, this technique can only be used on clear moonless nights, which significantly limits the viewing time.
Answers (e) and (f) were just put in there to confuse you and trick you, so give yourself a high 5 if you got this question right.
Solar panels and spectrophotometers (g) cannot be used to detect cosmic rays. Solar panels are used to generate electricity from the sun's energy and spectrophotometers are used to measure a photon spectra over a defined range of wavelengths.
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