A FAST SCINTILLATION DETECTOR FOR ANALYTICAL X-RAY INSTRUMENTS

Detectors used with X-ray diffraction and fluorescence instruments frequently encounter dead time limitations. Conventional systems employ a NaI(T1) scintillation detector and are constrained by the scintillation decay constant. A detector was constructed which consisted of a relatively fast plastic scintillator coupled to two photomultipliers operated in coincidence. The coincidence gate reduced noise from random photomultiplier dark current pulses. The scintillator was shaped so that total internal reflection tended to collimate scintillation light, and it was shown that this increased quantum efficiency. Fast counting electronics were built using ECL gates; this included coincidence gate, single channel analyzer, and afterpulse rejection circuitry. System dead time was 37 ns. When adjusted to observe 8.1 keV X-rays, noise pulse rate was 2.0 s−1, and quantum efficiency was 86%. Copyright © 1990 by The Institute of Electrical and Electronics Engineers, Inc.