A gain monitoring system for scintillation detectors using ultra bright LEDs

A gain monitoring system based on ultra bright LEDs was developed for the scintillation counters of the PiP/TOF detectors to be employed in (γ, NN) experiments at the 855 MeV microtron MAMI-B in Mainz. The intensive light pulses of one LED supplied 16 photomultipliers simultaneously and one PIN diode for monitoring. The stability of the corrected photomultiplier gain is better than 0.5%. The LED pulses were also used to calibrate the time walk of the leading edge discriminators.