Abstract Polyvinyl toluene (PVT) based detectors are used in radiation portal monitors (RPMs) throughout the world to detect the trafficking of illicit nuclear material. PVT scintillators, which are normally optically clear, have been observed to suffer internal fogging throughout their volume due to prolonged exposure to varying environmental conditions. These changes could lead to reduced performance for RPMs that utilize plastic scintillators. In this research, a proof of concept system, consisting of different color light emitting diodes (LEDs) and a single optical sensor (OS), were used to examine the change in light transmission through a PVT scintillator. This Optical Monitoring System (OMS), coupled with an environmentally exposed PVT detector, was tested in an environmental chamber where it was subjected to changes in temperature and humidity ranging from 55 °C at 100% relative humidity to -20 °C at 40% relative humidity. At temperatures below 10 °C, light transmission was reduced by 81% ± 8% for blue LEDs, 84% ± 5% for yellow LEDs, and 49% ± 4% for green LEDs. Similar reductions in detected light were not recorded when the OMS was tested with only air between the LEDs and OS. Therefore, the significant reductions in transmitted light were attributed to changes occurring within the PVT scintillator. These results indicate that a significant reduction in PVT opacity occurs due to wide environmental changes. A device such as the OMS could be used to track these changes and provide users an early indication that a portal monitor is suffering from reduced performance.

中文翻译：

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用于测量聚乙烯甲苯闪烁体不透明度变化的光学传感器的开发

摘要 基于聚乙烯甲苯 (PVT) 的探测器被用于世界各地的辐射门户监测器 (RPM) 以检测非法核材料的贩运。PVT 闪烁体通常在光学上是透明的，但由于长时间暴露在不同的环境条件下，它们的整个体积都会出现内部雾化。这些变化可能会导致使用塑料闪烁体的 RPM 性能下降。在这项研究中，概念验证系统由不同颜色的发光二极管 (LED) 和单个光学传感器 (OS) 组成，用于检查通过 PVT 闪烁体的光传输变化。该光学监测系统 (OMS) 与暴露在环境中的 PVT 探测器相结合，在环境室中对其进行了测试，在该环境中，它经历了从 100% 相对湿度下的 55 °C 到 40% 相对湿度下的 -20 °C 的温度和湿度变化。在低于 10 °C 的温度下，蓝色 LED 的透光率降低 81% ± 8%，黄色 LED 降低 84% ± 5%，绿色 LED 降低 49% ± 4%。当 OMS 仅在 LED 和 OS 之间有空气的情况下进行测试时，未记录到检测到的光的类似减少。因此，透射光的显着减少归因于 PVT 闪烁器内发生的变化。这些结果表明，由于广泛的环境变化，PVT 不透明度显着降低。OMS 等设备可用于跟踪这些变化，并为用户提供门户监视器性能下降的早期迹象。