1) Light Leaks
GOAL : determining the detector is in working order and capable of detecting high-energy particles.
CAUTION : perform this in a darkened room ! The room does not need to be totally dark, just mostly dark. IF THE PMT IS POWERED UP AND THERE IS A SIGNIFICANT LIGHT LEAK, THE PMT WILL FRY & DIE !!!!! So assume your detector leaks, and start it with low ambient light.
a) darken room
b) connect signal cable from PMT to oscilloscope
c) Without connecting to the PMT, power up your high voltage supply and test the voltage using a multimeter and a high voltage probe. If you're vague on this step, get help so you can do it right. The high voltage power supplies are evolving, so you need to learn how to do this with YOUR SPECIFIC equipment.
d) power down your high voltage supply and connect it to the PMT
e) Dark Room ! Power up your PMT. You might need to change settings on your oscilloscope to obtain a picture of a signal. It's very helpful at this point to have a low-level radioactive source, such as a piece of orange Fiestaware, to place on top of your sealed scintillator. This radioactive source should produce a visible signal, which should decline as you remove the source. If you can't get this to work, perhaps your scope is set incorrectly.
f) Use a flashlight to illuminate all parts of the detector and PMT. There should be no change WHATSOEVER in the oscilloscope display as you do this. Any point at which the signal jumps indicates a light leak, and should be examined and resealed with tape or paint. CAUTION : TURN OFF THE HIGH VOLTAGE SUPPLY BEFORE RESEALING !
g) Turn on room lights. There still should be no signal change, if you have a light-proof detector.