A microgap photomultiplier for the read-out of a LaF3:Nd(10%) scintillator

A LaF3:Nd(10%) scintillator crystal has been placed in a microgap gas chamber to obtain a position-sensitive detector for γ-rays. Directly on the crystal a thin layer of nickel is evaporated and on top of that a thin semi-transparant CsI photocathode. γ-rays absorbed in the scintillator crystal produce a UV-light flash, which liberates electrons 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 γ-rays with a spectrum that is computed in a Monte Carlo simulation it is concluded, that the probability that a UV-light photon created in the scintillator produces a photoelectron 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.