Light Testing the Scintillation Plate/PMT Units

Chad Webber and Tom Iannarelli

It is very important to make sure that the plates are light tight because that is what the PMT's are designed to sense.  If the assembly lets in light then we will not get a true reading of the number of cosmic rays.  Therefore, once it is wrapped it must be tested for light leaks.  This can be done by running the output from the assembly to the discriminator and then to the counter.  Set the voltage such that you see a steady flow of counts.  And set the threshold as low as it will allow in order to distinguish between light and noise.  Once this is set up you simply run a light across the whole detector while watching the counter; if the counter shows alot of counts at once, then go over it again to make sure that you might be leaking light.  If it is a leak then use some black tape to seal up the hole and repeat until you finish the whole plate.