Research On One Kind Of CCD Anti-coincidence Detector

Hard X-ray Modulation Telescope (HXMT) is a wide-band Survey Telescope based on the direct demodulation imaging method. There will be amount of charged particles getting through the high-energy、medium-energy and low-energy X-ray (HE> ME and LE) main detector when the HXMT satellite operates on orbit, and charged particles energies will be accumulated on the detector surface, which will lead to the generation of many backgrounds. The sensitivity of the main detector will be greatly influenced by the backgrounds then. The CCD detector which is used as the main detector for the low energy X-ray detection part will also be influenced by the charged particles getting through HXMT. Anti-coincidence detector is necessary to remove this part of backgrounds to eliminate the influence caused by the charged particles. In this paper, a CCD anti-coincidence detector has been designed to remove the signal generated by the charged particles emitting to the low energy main detector surface. The sensitivity of the LE CCD detector will be improved after that. The main frame and results in this paper are as follows.First of all, the design of the anti-coincidence detector has been conducted. The plastic scintillator has been adopted as the detection medium. Silicon photomultiplier tubes have been used as optical readout devices. The silicon photomultiplier has been coupled to a plastic scintillator by a light guide, and the surface of the plastic scintillator has been covered with a reflective layer and non-light layer. Type and size of the plastic scintillator have been decided. Meanwhile, type of the silicon photomultiplier has been selected.Secondly, the design of the electronics part has been achieved, including power modules, a front amplifier module and a linear amplifier module. Since the gain of the silicon photomultiplier (also called as Multi-pixel Photon Counter according to the principle. MPPC) changes obviously with temperature variation, which can greatly affect the performance of anti-coincidence detector. The tests of MPPC performance have been conducted. In order to stabilize MPPC gain, a temperature compensation circuit has been designed to solve this problem.Finally, some tests of the whole anti-coincidence detector unit have been conducted. The μ particle emitting to the ground has been chosen as the incident particle. By two-fold and triple coincidences, some performance tests of the anti-coincidence detector have been conducted. The results show that the detection efficiencies of the designed detector to all penetrating charged particles are higher than90%and the design requirement can be satisfied.