A MICROGAP PHOTOMULTIPLIER FOR THE READ-OUT OF A LAF3-ND(10-PERCENT) SCINTILLATOR

A LaF3:Nd(10%) scintillator crystal has been placed in a microgap gas chamber to obtain a position-sensitive detector for gamma-rays. Direct ly on the crystal a thin layer of nickel is evaporated and on top of t hat a thin semi-transparant CsI photocathode. gamma-rays absorbed in t he scintillator crystal produce a UV-light flash, which liberates elec trons in the photocathode. These electrons are multiplied and detected in the microgap chamber. By comparing the spectrum measured when this detector is irradiated with 511 keV gamma-rays with a spectrum that i s computed in a Monte Carlo simulation it is concluded, that the proba bility that a UV-light photon created in the scintillator produces a p hotoelectron in the photocathode, is about 2.5%. The signals from this detector can be distinguished better from the background than when a similar crystal is mounted on a standard photomultiplier tube. (C) 199 8 Elsevier Science B.V. All rights reserved.