Stabilizing scintillation detector systems with pulsed LEDs: a method to derive the LED temperature from pulse height spectra

Photomultiplier tubes are often stabilized with pulsed LEDs used as reference light sources. However, if detectors must be operated in a wide temperature range, the temperature dependence of the LED light emission must be considered as well. Such demanding conditions are typical for outdoor applications, e.g. in the field of homeland security. This problem is solved by means of a new method. The actual LED temperature is derived from a measured pulse height spectrum while the LED is operated in two alternating modes distinguished by different pulse voltages. Since the temperature dependence of the light output varies with the pulse voltage, the ratio R of the peak positions corresponding to different voltages is a function of the LED temperature as well. This ratio can be determined with an unstable PMT. Measuring L and determining R at different temperatures yields a calibration function L(R). With this knowledge, commercial off-the-shelf LED components can be used as precision light sources in a wide range of ambient temperatures.