Lutetium oxyorthosilicate or lutetium yttrium oxyorthosilicate (LYSO) scintillation crystals used in most current PET scanner detectors contain 176Lu, which decays by beta emission to excited states of 176Hf accompanied by the emission of prompt gamma rays or internal conversion electrons. This intrinsic radioactivity can be self-detected in singles mode as a constant background signal that has an energy spectrum whose structure has been explained previously. In this work, we studied the energy spectrum due to the intrinsic radioactivity of LYSO scintillation crystals of two opposing detectors working in coincidence mode. The investigation included experimental data, Monte Carlo simulations and an analytical model. The structure of the energy spectrum was completely understood and is the result of the self-detection of beta particles from 176Lu in one crystal and the detection of one or more prompt gamma rays detected in coincidence by the opposing crystal. The most probable coincidence detection involves the gamma rays of 202 and 307 keV, which result in two narrow photopeaks, superimposed on a continuous energy distribution due to the beta particle energy deposition. The relative intensities of the gamma ray peaks depend on crystal size and detector separation distance, as is explained by the analytical model and verified through the Monte Carlo simulations and experiments. The analytical model used in this work accurately explains the general features of the coincidence energy spectrum due to the presence of 176Lu in the scintillation crystals, as observed experimentally and with Monte Carlo simulations. This work will be useful to those research studies aimed at using the intrinsic radioactivity of LYSO crystals for transmission scans and detector calibration in coincidence mode.

中文翻译：

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由于LYSO闪烁晶体的固有放射性而产生的重合能谱。

大多数当前的PET扫描仪中使用的原硅酸or或原硅酸（闪烁晶体（LYSO）含有176Lu，它会因β发射而衰减到176Hf的激发态，并伴随着迅速的伽马射线或内部转换电子的发射。这种固有的放射性可以作为具有恒定能谱的恒定背景信号在单模模式下自我检测，该能谱的结构已在前面进行了解释。在这项工作中，我们研究了以同时模式工作的两个相对探测器的LYSO闪烁晶体的固有放射性所引起的能谱。调查包括实验数据，蒙特卡洛模拟和分析模型。能谱的结构已被完全理解，并且是一种晶体中自176Lu的β粒子的自我检测结果以及对立晶体同时检测到的一种或多种快速伽玛射线的检测结果。最可能的重合检测涉及202和307 keV的伽马射线，这会导致两个狭窄的光峰，由于β粒子能量的沉积，它们叠加在连续的能量分布上。伽马射线峰的相对强度取决于晶体尺寸和检测器分离距离，如分析模型所解释，并已通过蒙特卡洛模拟和实验验证。这项工作中使用的分析模型准确地解释了由于闪烁晶体中存在176Lu而引起的重合能谱的一般特征，如通过实验和蒙特卡洛模拟观察到的。这项工作对于那些旨在将LYSO晶体的固有放射性用于重合模式下的透射扫描和检测器校准的研究将是有用的。