Abstract At the European Spallation Source (ESS), a Target Imaging System (TIS) has been proposed to monitor the integrity of the target wheel. The TIS signal will be provided by the gamma decay photons from the activated tungsten bricks of the target. To collect the photons, a linear array of 500 scintillators is mounted on a collimator and the imaging is achieved via a push-broom method. Scintillation light will be carried by optical fibers to an intensified sCMOS camera. This study presents a characterization of the performance of the full detector chain: emission from crystals, attenuation in optical fibers and response of the camera optics. The behaviour of both unirradiated and irradiated optical fibers is also evaluated for γ-only irradiations up to 15 kGy . Among the tested crystals (LuAG:Ce, YAG:Ce and BGO), LuAG:Ce is the preferred choice both in terms of radiation hardness and photon yield. Losses induced by Poly methyl methacrylate (PMMA) and quartz optical fibers are ~ 65 % and ~ 45 % , respectively. In ESS conditions, over half-year of continuous operations, PMMA fibers are estimated to lose an additional 3 % , compared to 2% for quartz fibers. Both PMMA and quartz fibers represent a potentially viable choice: the former suffer a more serious radiation damage than the latter, but formation of permanent defects in quartz can impair the efficiency of quartz fibers in the 580 − 620 nm range. Mix-and-match of PMMA and quartz fibers may represent a cost-effective compromise for the final TIS design. Two different fibers-camera coupling optics are compared. The measured difference in transmittance is 3 % .

中文翻译：

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ESS 目标成像系统的光学元件表征

摘要 在欧洲散裂源（ESS），已经提出了一种目标成像系统（TIS）来监测目标轮的完整性。TIS 信号将由来自目标激活钨砖的伽马衰变光子提供。为了收集光子，将 500 个闪烁体的线性阵列安装在准直器上，并通过推扫式方法实现成像。闪烁光将由光纤传送到增强型 sCMOS 相机。这项研究展示了整个探测器链的性能特征：晶体的发射、光纤的衰减和相机光学元件的响应。还针对高达 15 kGy 的仅 γ 辐照评估了未辐照和辐照光纤的行为。在测试的晶体（LuAG:Ce、YAG:Ce 和 BGO）中，LuAG：就辐射硬度和光子产额而言，Ce 是首选。聚甲基丙烯酸甲酯 (PMMA) 和石英光纤引起的损耗分别为 ~ 65 % 和 ~ 45 %。在 ESS 条件下，连续运行半年以上，估计 PMMA 纤维会额外损失 3%，而石英纤维则为 2%。PMMA 和石英纤维都代表了一种潜在的可行选择：前者比后者遭受更严重的辐射损伤，但石英中永久缺陷的形成会损害石英纤维在 580 - 620 nm 范围内的效率。PMMA 和石英纤维的混合搭配可能代表最终 TIS 设计的成本效益折衷。比较了两种不同的光纤-相机耦合光学器件。测得的透射率差异为 3%。