A prototype of aerial radiation monitoring system using an unmanned helicopter mounting a GAGG scintillator Compton camera

Due to the accident of Fukushima Daiichi Nuclear Power Plant, some areas were contaminated by released radioisotopes (mainly 137Cs and 134Cs). Effective decontamination is demanded to encourage evacuated people to return. This paper proposes a new survey system using an unmanned helicopter equipped with a Compton camera for localizing radionuclides. As a prototype, 32 Ce:Gd3(Al,Ga)5O12 (GAGG) crystals were coupled to 16 silicon photomultipliers and 16 avalanched photodiodes as the scatterer and absorber, respectively. A new Dynamic Time-over-Threshold (dToT) method was applied to convert CR-RC shaping signals to digital signals for multi-channel spectra and coincidence acquisition. The system was designed to work in two modes: one is Compton-camera mode (CCM) which obtains the radiation distribution maps through Compton imaging using hovering flights, while the other one is Gamma-camera mode (GCM) which maps the radiation distribution via measured coincidence events using programmed flights. For point source in CCM, an intrinsic efficiency of 1.68% with a combined standard uncertainty of 0.04% and an angular resolution of about 14° (FWHM, full width at half maximum) was achieved. In GCM, a spatial resolution of about 11 cm (FWHM) was obtained when detecting area is 11.2 cm away from the detector, while it was about 28 cm (FWHM) in single detector mode (SDM). Promising results were obtained in field in Fukushima.

[1]  Shunsuke Kurosawa,et al.  Cz grown 2-in. size Ce:Gd 3 (Al,Ga) 5 O 12 single crystal; relationship between Al, Ga site occupancy and scintillation properties , 2014 .

[2]  V. Chani,et al.  Czochralski growth of Gd 3 (Al 5−x Ga x )O 12 (GAGG) single crystals and their scintillation properties , 2014 .

[3]  Tetsuzo Yasunari,et al.  Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident , 2011, Proceedings of the National Academy of Sciences.

[4]  Tatsuo Torii,et al.  A Remote Radiation Monitoring System Using an Autonomous Unmanned Helicopter for Nuclear Emergencies , 2008 .

[5]  Tatsuo Torii,et al.  Development of a remote radiation monitoring system using unmanned helicopter , 2005 .

[6]  Shinji Ohsuka,et al.  Handy Compton camera using 3D position-sensitive scintillators coupled with large-area monolithic MPPC arrays , 2013 .

[7]  Boxuan Shi,et al.  Dynamic Time Over Threshold Method , 2012, IEEE Transactions on Nuclear Science.

[8]  Yasushi Fukazawa,et al.  High-Resolution Compton Cameras based on Si/CdTe Double-Sided Strip Detectors , 2012 .

[9]  Andreas Zoglauer,et al.  Simulation and detector response for the High Efficiency Multimode Imager , 2011 .

[10]  T. Takahashi,et al.  A Si/CdTe semiconductor Compton camera , 2004, IEEE Transactions on Nuclear Science.

[11]  Feng Zhang,et al.  4-pi Compton imaging with single 3D position-sensitive CdZnTe detector , 2004, SPIE Optics + Photonics.

[12]  T. Tomitani,et al.  Image reconstruction from limited angle Compton camera data , 2002, Physics in medicine and biology.

[13]  L. Parra,et al.  Reconstruction of cone-beam projections from Compton scattered data , 1999, 1999 IEEE Nuclear Science Symposium. Conference Record. 1999 Nuclear Science Symposium and Medical Imaging Conference (Cat. No.99CH37019).

[14]  Yukihisa Sanada,et al.  Aerial radiation monitoring around the Fukushima Dai-ichi Nuclear Power Plant using an unmanned helicopter. , 2015, Journal of environmental radioactivity.