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

我们一直在研制一种新型的伽玛射线望远镜，用气球发射，用于未来的卫星实验。该望远镜由一个跟踪系统和一个量热计组成，前者用于探测伽马射线对的产生，后者用于测量能量。采用闪烁光纤探测伽玛射线诱导的带电粒子，采用紧凑型16阳极PMT读取每条光纤的信号。该量热计由厚度为8辐射长度的分段铯晶体组成。仿真结果表明，该望远镜比传统的利用火花室探测双子星的望远镜具有优势。预计该望远镜将在探测效率、紧凑性和准备性等方面优于现有的CGRO望远镜EGRET。人们认为，在与EGRET重量几乎相同的情况下，有可能研制出一种有效面积比EGRET大10倍的望远镜。通过仿真和加速器测试，对探测器各部分的性能进行了优化。经核科学研究所电子束实验证实，该量热计在能量分辨率和位置分辨率上都达到了预期的性能。由16根闪烁光纤组成的跟踪系统单元（每根光纤的横截面为2mm）和16个阳极PMT被照射到CERN-PS的质子束上。它可以以接近100%的效率和0.6 mm的位置分辨率检测最小电离粒子。由于该系统具有快速触发的功能，因此可以通过检测具有对产生特征的命中模式，作为强子背景下的有效反偶合系统。在研制了多通道读出ADC系统和气球有效载荷支撑后，我们将在两年内开展气球观测。

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.