Development of Gamma-ray Detector System with Light Weight for Drone

In case of nuclear and radiation accidents with high risk of radiation exposure such as Chernobyl and Fukushima nuclear accident, it is important to detect radioactive materials and collect radiation dose information for... [ view full abstract ]

In case of nuclear and radiation accidents with high risk of radiation exposure such as Chernobyl and Fukushima nuclear accident, it is important to detect radioactive materials and collect radiation dose information for on-site control. Above all, detecting gamma rays is essential because the gamma ray emitted by radioactive materials can damage the human body.Therefore, if a gamma ray detector is loaded in a drone that can move freely and detect regardless of the terrain, we can cope with nuclear accident promptly. But, it is difficult to install a gamma ray detection system that combines a conventional PMT (Photomultipliers) detector and a collimator, which is heavy and consumes relatively high power because of limited battery capacity and limited payload. In this study, we focused on the development of a gamma ray detector system with the same or better performance while reducing the weight of the system.

First, we optimized the structure of the scintillator which occupies more than 80% of the weight in the detector. The gamma ray detector to be optimized is simply composed of scintillator, light guide and light sensor. For optimization simulation, a Vgate which can simulate visible light used, one of Monte Carlo simulation tools. As shown in figure 1 and table 1, three types of scintillator having same weight were compared and analyzed for optimizing scintillator structure. The evaluation of the gamma ray detector was performed as detector efficiency, light collection efficiency and energy resolution which are important evaluation factors of spectroscopy. Cone type gamma ray detector has superior performance to the other two detectors.

Second, the effective dose received by the person on the ground was predicted through the visible light spectrum measured at SiPM over 50 m without the collimator. Figure 2 shows fluence depending on distance when measuring at 1 m which is the midpoint of the human and 50 m. From the results of height 1m, we can check that the source out of radius 300m did not contribute to the signal. Likewise in the case of the height of 50m, the source out of radius 500m did not contribute to the signal. And we suggest a method which converts 50m spectrum data to the effective dose that people can receive on the ground.