DETECTION OF MONOCHROMATIC PHOTONS BETWEEN 50 AND 790 MEV WITH A PBWO4-SCINTILLATOR ARRAY

The performance of PbWO4 as a fast an compact scintillator material fo r calorimetry at energies well below 1 GeV has been investigated using a collimated beam of monoenergetic photons with an energy between 50 and 790 MeV provided by the tagged photon facility of MAMI at Mainz. I n continuation of previous experiments with electrons, a larger matrix of 5x5 PbWO4-crystals (20x20x150-200mm(3)) has been used to reconstru ct the electromagnetic shower. The scintillators were selected accordi ng to their optical quality and response to low energy gamma-sources. The array was operated at a stabilized temperature of T = 8 degrees C and read-out individually by photomultiplier tubes. The achieved excel lent energy resolution amounts to sigma/E = 1.54%/root E + 0.30% (E gi ven in GeV) and has proven the applicability of PbWO4 as a high qualit y scintillator material even at medium energies. The experimental data have been reproduced by GEANT3 simulations.