采用偏振器的康普顿旋光仪通过Citiroc ASIC用MPPC读出
A Compton polarimeter using scintillators read out with MPPCs through Citiroc ASIC
摘要：
近年来，一些专门建造的基于偏振器的偏振计首次研究了硬X射线波段（数十至数百keV）的明亮天文源。增加旋光可以通过解决依赖于模型的简并来帮助数据解释。典型的仪器方法是入射X射线从塑料闪烁体散射到相邻的闪烁体单元中。在迄今为止的所有特派团中，使用传统的真空管光电倍增管读出光放大器。固态光电倍增管（“硅PM”或“MPPC”）的出现对空间仪器很有吸引力，因为这些设备紧凑、坚固且需要低偏置电压。我们已经表征了塑料闪烁体，EJ-248 M，光学耦合到多像素光子计数器（MPPC）和读出与Citiroc ASIC。在室温下获得了1.6个光电子/keV的光产额，低能量探测阈值为$\lesssim$ 5 keV。我们还建造了一个基于MPPC的偏振仪演示，以探讨这种方法的可行性，为未来的仪器。入射X射线从塑料闪烁体棒散射到周围的掺铈GAGG（钆铝镓石榴石）闪烁体，在闪烁体中产生时间重合信号。我们已经确定了使用非极化和极化$\sim$ 50 keV X射线的极化响应。我们观察到一个明显的不对称性的GAGG计数率的偏振光束。塑料闪烁体中的低能量检测阈值可以使用符合技术进一步降低。演示偏振计的设计显示作为一个空间为基础的康普顿偏振计的承诺，我们讨论的方式，我们的偏振计可以适应这样的任务。
英文摘要：
In recent years, a number of purpose-built scintillator-based polarimeters have studied bright astronomical sources for the first time in the hard X-ray band (tens to hundreds of keV). The addition of polarimetry can help data interpretation by resolving model-dependent degeneracies. The typical instrument approach is that incident X-rays scatter off a plastic scintillator into an adjacent scintillator cell. In all missions to date, the scintillators are read out using traditional vacuum tube photo-multipliers (PMTs). The advent of solid-state PMTs ("silicon PM" or "MPPC") is attractive for space-based instruments since the devices are compact, robust and require a low bias voltage. We have characterised the plastic scintillator, EJ-248M, optically coupled to a multi-pixel photon counter (MPPC) and read out with the Citiroc ASIC. A light-yield of 1.6 photoelectrons/keV has been obtained, with a low energy detection threshold of $\lesssim$5 keV at room temperature. We have also constructed an MPPC-based polarimeter-demonstrator in order to investigate the feasibility of such an approach for future instruments. Incident X-rays scatter from a plastic-scintillator bar to surrounding cerium-doped GAGG (Gadolinium Aluminium Gallium Garnet) scintillators yielding time-coincident signals in the scintillators. We have determined the polarimetric response of this set-up using both unpolarised and polarised $\sim$50 keV X-rays. We observe a clear asymmetry in the GAGG counting rates for the polarised beam. The low-energy detection threshold in the plastic scintillator can be further reduced using a coincidence technique. The demonstrated polarimeter design shows promise as a space-based Compton polarimeter and we discuss ways in which our polarimeter can be adapted for such a mission.
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