Muons that are traveling down towards the earth can be detected by a scintillation detector. The scintillation detector contains a material that fluoresces when struck by radiation. A photomultiplier can then be used to measure this fluoresce, thus indicating when a muon has entered the detector. It is important to note that the detector will not only fluoresce when a muon is detected. Muon decay into a positron or an electron will also cause the detector to fluoresce as will almost any other radiation. A voltage discriminator can be used to screen out low energy events, but this alone will not eliminate all the background radiation.