大视场γ射线偏振能谱仪的设计研究

Measurement of energy spectrum and polarization properties simultaneously in X/γenergy range is important to revealing the radiation mechanism and geometric construction of compact object in high energy astrophysics. It is a great scientific potential research area now. For a typical Gamma-Ray Burst spectrum, polarization is determined by measuring the azimuth distribution of Compton scattering photons. POLAR, GRAPE, PoGOLite etc. are designed by this principle. The reconstructions of polarization properties and localization are energy dependent. However, the current several Compton polarimeters do not have the ability of measuring the energy spectrum and polarization properties simultaneously with a large FOV. In this research, optimized arrangement of plastic and high-Z scintillator bars is a key issue. Innovatively, two SiPMs , as readout devices, are coupled to both ends of each scintillator bar. This leads to an large FOV instrument, which not only has the ability of self-localized the γ-source, but also has the capability to measure energy spectrum and polarization properties simultaneously. This instrument is very fit for observing transient sources and GRB. This instrument could be used as a dedicated γ-ray spectrum-polarimetry or a GRB all-sky monitor. It is suit to be a candidate payload aboard on a micro-satellite or a large space-borne platform.

空间X/γ射线的偏振测量及其能量相关性为人们了解高能天体的辐射机制和几何结构提供了关键信息，是目前高能天体物理观测领域新兴的研究热点。在伽马暴GRB典型波段，偏振仪器的设计是通过测量Compton散射光子出射方位角的偏振调制效应推算入射光子的偏振信息，如POLAR、GRAPE、PoGOLite等专用的γ射线偏振仪。GRB偏振信息及入射γ源空间定位的能力是依赖于入射能谱的，而现有仪器的设计均无法实现兼具大视场和偏振能谱联合观测的能力。本项目研究使用塑料闪烁体和高Z闪烁体共同组成探测器阵列，创新性的使用SiPM对每根闪烁体棒进行双端读出，可实现对入射γ射线源自主定向，具备入射γ射线偏振信息和能谱联合观测的能力，兼具有大视场的优点，十分适用于暂现γ射线源和伽马暴的巡天观测。其研究成果将可以用作γ射线偏振能谱仪或伽马暴全天监测器的目的，做为空间微小卫星项目或大型平台搭载项目的科学载荷候选。

偏振和能量同时测量对限制伽马暴辐射机制和几何模型具有重要意义，而目前高能偏振测量仪基本都设计成了专用的偏振测量仪器，不能同时进行能谱和偏振联合测量。.本项目的研究目标是对伽马暴偏振仪进行设计，在保持大视场FOV的基础上，通过探测器布局优化设计，实现偏振信息、能谱信息及自主定向信息的同步测量。主要研究内容包括探测器布局优化设计研究，利用SiPM对闪烁体棒双端读出技术验证，自主定位算法研究。目前这些研究内容基本完成，达到了预期，初步验证了方案可行性。. 基于Compton散射原理，用放射源搭建了偏振度及能量可调的偏振X射线源，能区覆盖50-500keV，偏振度20%-86%可调。确定每个探测器模块由塑料和CsI闪烁体组成9*10的阵列，只用四个探测器单元就可以实现自主定位精度优于5°。 SiPM双端符合读出可以将暗计数降低约4个数量级，探测能量下阈约20keV。.基于研究结果提出了宽波段X/γ射线能谱与偏振卫星概念，实现3-500keV能区偏振能谱探测，并列入了某部门十四五民用航天计划指南中。