摘要:
中国科学院近代物理研究所气体探测器组研制了一种大型位置灵敏的平行板雪崩计数器（PPAC）。它主要由中心阴极和
X，
Y位置阳极构成，灵敏面积为244 mm×284 mm，阴极为双面镀金1.5 μm厚的Mylar膜，阳极为直径20 μm，间距1 mm的镀金钨丝。位置读出选用延迟块读出法。这种探测器经测试在灵敏面积内位置分辨小于4 mm，时间分辨为0.42 ns，已在兰州放射性束流线（RIBLL）上清华大学的核反应实验中使用。该实验中使用了主束
40Ar直接轰击Au靶，产生裂变碎片，使用了4个这种大型位置灵敏的PPAC，用来探测裂变碎片的飞行时间和速度，实验表明，PPAC对裂变碎片有90.3%的效率，给出了裂变碎片的位置分布，为理论分析工作提供了非常好的实验数据。
A kind of large position sensitive parallel plate avalanche counter(PPAC) was developed at Gas Detector Research Group, Institute of Modern Physics of CAS. Each of the detector with large sensitive area of 244 mm×284 mm, consists of one central cathode,
X anode and
Y anode. The cathode plane in the middle of detector is a 1.5 μm thick Mylar foil coated with a thin Au-layer on both sides. The position resolution of the PPAC is better than 4 mm, and the time resolution is 0.42 ns. The detectors were used in the fission experiment with 30MeV/u
40Ar beam bombarding on a gold target to measure the velocity of the fission fragments at Radioactive Ion Beam Line In Lanzhou(RIBLL). Four PPACs were used and the experiment result showed that a rather high detection efficiency (90.3%) is achieved. The position distribution of fission fragments is given by PPACs, which provides very good experimental data for further theoretical analysis.
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