Development of a -detector with barium fluoride crystal

本项目的目的是研制一种满足以下性能要求的探测器：（1）良好的能量分辨率（在1GeV时<2%），（2）良好的位置分辨率（<8 mm），（3）快速响应（死时间<100 nsec），（4）大面积覆盖。考虑两种类型的材料：氟化钡（BaF 2）和纯碘化铯（纯CsI）。1. BaF 2有两种闪烁成分。快的一个具有=220 nm的峰值发射波长和=0.6 nsec的衰减时间，而慢的一个具有=310 nm和=610 nsec。为了消除对应用不利的慢分量，我们采用了一种带cste光电阴极的光电倍增管。结果，慢分量减少了约5倍。研制了一个120 mm × 120 mm × 300 mm的测试探测器，并用0.8 GeV电子束进行了测试。所得的能量分辨率为4.2%，这不符合我们的上述要求。这部分是由于晶体尺寸;因此需要改进晶体生长技术以获得更长的晶体。纯CsI也有两种闪烁成分。最快的一个具有=310 nm和=10 nsec。它的光产额约为NaI（TI）分解剂的4%。用1.2GeV电子束对150 mm × 150 mm × 300 mm的A型探测器进行了测试。能量分辨率为1.84%。因此，该材料已被证明是一个有前途的候选人的高速率检测器。

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.