A scientist from Fermilab's particle detection group examines a scintillator test sample. These samples will be used to detect Cosmic rays, subatomic particles possessing a large range of energy. Thousands of these rays pass through a square meter every second. When these charged particles pass through a scintillator they excite the atoms in the plastic. The excited atoms emit photons of light. The light is detected by a "photomultiplier" that multiplies the small flash of light into a measurement scientist can use to tell how many particles passed through the scintillator. The scintillators are housed in a dark box so that the only light detected that of the cosmic rays. The origin of cosmic rays is still not known.