When a cosmic ray (typically a proton or a heavier atomic nucleus) or a γ-ray (a high-energy photon) collides with a molecule in Earths atmosphere, it creates charged particles that start a chain reaction, cascading into a particle shower. When these secondary particles reach Earth’s surface and zip through one of HAWCs tanks, they travel through the water faster than does light. (In water, light trudges along at three-quarters of its speed in a vacuum.) The incoming particles excite the water molecules, which then emit photons as they return to their ground state. This optical phenomenon, in which a particle moves faster than the light cone it creates in its wake — much like a sonic boom in acoustics — is called Cherenkov radiation, and HAWCs tanks are known as Cherenkov detectors.
Posted on: Sun, 24 Nov 2013 00:39:46 +0000
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