Development of wide view gamma-ray Imaging Detector

提出了MeV γ射线成像的新方法。通过不仅测量散射伽马射线的方向和能量，而且测量散射电子的方向和能量，入射伽马射线的方向将被逐事件地基本重建，并且将实现全成像。此外，散射电子的两个测量（天顶角和方位角）角之一给co一个额外的冗余，使我们能够拒绝几乎所有的背景事件的运动学拟合。为了探测这种精细的反冲电子径迹，本文提出了一种利用微印制板技术制作的精细成像气体探测器，并研制了微型时间投影室（TPC），它可以在几百微米的间距内连续测量电子的三维径迹位置。该TPC包括一种新型的气体比例室：微像素气室（MPGC），这是一种无线气室，预计比微带气室更坚固可靠。研制了10 cm × 10 cm、像素间距为400 μm的2D-MPGC，获得了15000的高增益，并作为微型TPC稳定工作，在一个月内增益达到15000。此外，还研制了一台由10 cm × 10 cm ×2.5cm的NaI闪烁体和5×5的1英寸光电管阵列组成的小型Anguar照相机，用于探测反冲γ射线。利用微型TPC和Anguar相机，我们成功地获得了第一幅伽马射线图像，通过逐事件的伽马射线方向的完全重建。虽然由于MPGC的效率低下，获得的角分辨率不太好，但这是世界上第一次证明全伽马射线成像的可能性。

We have proposed the new imaging method of MeV gamma rays. By measuring the direction and energy of not only a scattered gamma ray but also a scattered electron, the direction of an incident gamma ray would be principally reconstructed event by event, and a full imaging would be realized. Furthermore, one of two measured (zenith and azimuthal) angles of a scattered electron gives co an additional redundancy which enable us to reject almost all the background events by kinematic fitting. In order to detect such a fine track of the recoil electron, a fine imaging gas detector made by the micro printed board technology was proposed here.In order to obtain 3-D track of a scattered electron, the micro Time Projection Chamber(TPC) has been developed, which measures the position of the track in a few hundred micron meter pitch successively. This TPC consists of the new type of a gas proportional chamber : Micro Pixel Gas Chamber (MPGC) which is a one of wireless gas chamber and expected to be more robust and reliable than Micro Strip Gas Chamber. Here 10cm×10cm 2D-MPGC with a 400 μm pitch pixel was developed, and the high gain of 〜 15000 and the stable operation as a micro TPC with a moderated gain of 〜 5000 during one month have been achieved. Also a compact Anguar camera consisting of a 10cm×10cm×2.5cm NaI scintillator and a 5×5 one-inch phototube array was constructed to detect a recoil gamma ray. Using the micro TPC and the Anguar camera, we successfully obtained the first gamma-ray image by the full reconstruction of the direction of gamma rays event by event. Although obtained angular resolution of 〜 30°is not so good due to the inefficiency of the MPGC, it is the first time in the world to demonstrate the possibility of full gamma ray imaging.