Detection of fast BaF2 scintillations with a CsI photocathode coupled to a MWPC

We have investigated the efficiency of a CsI photocathode in a MWPC for detection of the fast BaF₂ scintillation component, the variation of this efficiency over a period of two months and it´s behaviour under an elevated radiation level. We find an extrapolated initial yield of 13 photoelectrons per MeV of energy deposited in the scintillator. This yield decreased exponentially with two decay constants. During the first three weeks the decay constant amounted to 5% daily and then it reduced to 1% per day. No noticeable change in the photoelectron yield or it´s rate of decrease was observed after 3 days irradiation amounting to a collected charge of 0.3 mC/cm²