Observation of the GeV gamma-rays by a balloon-borne instrument

我们一直在研制一种新型的伽马射线望远镜，用气球发射，供将来的卫星实验使用。该望远镜由一个跟踪系统和一个量热计组成，跟踪系统用于探测伽马射线对的产生，量热计用于测量能量。用闪烁光纤探测γ射线引起的带电粒子，用紧凑型16阳极光电倍增管读出每根光纤的信号。量热计由厚度为8辐射长度的分段Csl晶体组成。模拟结果表明，该望远镜比用火花室探测对产生的传统望远镜具有优越性。该望远镜预计将上级目前的望远镜，EGRET上CGRO，在性能上的检测效率，紧凑性和易用性。在与EGRET质量相当的条件下，研制出有效面积比EGRET大10倍的望远镜是有可能的。在原子核研究所的电子束实验中证实了该量能计在能量和位置分辨率方面具有预期的性能。跟踪系统的一个单元由16根光纤组成在CERN-PS上用质子束辐照16阳极光电倍增管，探测效率接近100%，位置分辨率为0.6mm，由于系统具有快速触发功能，我们将在两年内完成ADC多通道读出系统的研制和气球有效载荷支持系统的建造后，进行气球观测。

We have been develping a new-type gamma-ray telescope to be lauched by balloon for future satellite experiment. The telescope is composed of a tracking system to detect pair-creation by gamma-ray and a calorimeter to measure the energy. Scintillating fibers are adopoted to detect the chareged particles induced by gamma-ray, and a compact-type 16-anodes PMT is to read the signals from each fiber. The calorimeter consists of segmented Csl crystals with a thickness of 8 radiation length. It is prdicted by simulations that the telescope has advantages to conventional one which detect the pair creation wiht a spark chamber. The telscope is expected to be superior to the current telescope, EGRET on CGRO,on the performance of detection efficiency, compactness and readiness. It is supposed to be possible to develop a telescope with a larger effective-area by ten times within nearly same weight to EGRET.Peformance of each part of the detector has been optimaized by simulations and tested by using accelerator beams. It was confirmed by the electron beam test at the ES of Institute of Nuclear Study that the calorimeter has an expected performance in the energy and positional resolution. A unit of the tracking system consisting of 16 scintillating fibers (2mm square cross-section for each) and the 16-anodes PMT was irradiated to the proton beams at the CERN-PS.It could detect a minimum ionizind particle with an efficiency of nearly 100 % and a positional resolution of 0.6 mm. Since the system can have function of fast trigger, it is expected to work as an efficient anti-conincidence system against the hadron backgrounds by detcting a hit pattern which is charcteresitic to the pair creation.We will carry out the balloon observation within two years after developing the ADC system for multi-channel read-out and constructing the balloon payload support.