A long term stable reference light source using LEDs for stabilization of scintillation spectrometers

This note reports on a reference light source using a green LED with a stabilized light output for photomultiplier gain stabilization systems. A stabilization system has been designed and constructed using a PIN-photodiode monitoring and stabilizing the light output of the light emitting diode. In measuring the LED light output per pulse an error signal is developed and fed back to the pulser unit flashing the LED. Thus, long-term instabilities of the LED light output, which are of the order of 0.1% per day, and its temperature dependence (about 0.5%/0C) are reduced to an overall stability of the system of 0.1% independent of time and temperature variations between 100C and 350C. This LED reference light source can be employed in all types of photomultiplier gain stabilization systems used according to the experimental requirements. (orig.)