Detecting a Coincidence

A Cosmic Ray through two Scintillation Plates

Tom Iannarelli and Chad Webber

Coincidence The comic ray telescope is two scintillating plates held in parallel planes with an 18 inch separation. A coincidence occurs when a cosmic ray passes through both plates. The PMTs produces signals from thermal energy (noise) as well as cosmic rays. Noise signals occur at kilohertz rate and are very unlikely to occur in both plates at the same instant. Signals from cosmic rays WILL occur in both plates within nanoseconds, which produces a coincidence.

The signals from the two PMTs are discriminated to produce a digital pulse. The digital pulses are sent to an AND gate. If both inputs of the AND gate are high indicating signals, the output goes high and the coincidence is observed and counted on a scalar. The coincidences can be detected at a megahertz rate.

Last updated:15 June 2001
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