Development of a -detector with barium fluoride crystal

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The purpose of this project is to develop a -detector which satisfies following performance requirements; (1) good energy resolution (<2% at 1 GeV), (2) good position resolution (<8mm), (3) fast response (dead time<100 nsec), (4) large area coverage. Two types of material were considered: barium fluoride (BaF2) and pure cesium iodide (pure CsI).1. BaF2 has two scintillation components. The fast one has a peak emission wave length of =220 nm and a decay time of =0.6 nsec while the slow one has =310 nm and =610 nsec. In order to remove the slow component, which is harmful to our application, we have employed a photomultiplier with a cste photocathode. As a result, the slow component was reduced by factor about 5. A test detector (120mmx120mmx300mm) was constructed and tested with a 0.8-GeV electron beam. The resultant energy resolution was 4.2%, which does not fulfil our requirement above. This is partly due to the crystal size; thus improvement in a crystal-growth technique for longer crystals is needed.2. There are also two scintillation components for pure CsI. The fast one has =310 nm and =10 nsec. Its light yield was found to be about 4% of NaI(TI) scintillators. A -detector (150mmx150mmx300mm) was constructed and tested with a 1.2 GeV electron beam. An energy resolution of 1.84% was obtained. Thus the material has proved to be a promising candidate for a high rate -detector.