The stabilization of a positron lifetime spectrometer with a high-accuracy time reference

A high-accuracy time reference for a fast coincidence apparatus using scintillation detectors is constructed. The reference peak is created by feeding fast light pulses from a light-emitting diode along two optical fibers of different lengths onto the photomultipliers. The peak can serve as a basis of digital hardware or software stabilization. A particular advantage of the system is that the accuracy of drift detection can be enhanced notably by using a high frequency in the reference peak. In a one-week-long test measurement with a positron lifetime spectrometer, drifts of 12 ps were reduced below a level of 0.5 ps with hardware stabilization.