Handy Compton camera using 3D position-sensitive scintillators coupled with large-area monolithic MPPC arrays

The release of radioactive isotopes (mainly Cs-137, Cs-134 and till) from the crippled Fukushima Daiichi Nuclear Plant remains a serious problem in japan. To help identify radiation hotspots and ensure effective decontamination operation, we are developing a novel Compton camera weighting only 1 kg and measuring just similar to 10 cm(2) in size. Despite its compactness, the camera realizes a wide 180 degrees field of vision with a sensitivity about 50 times superior to other cameras being tested in Fukushima. We expect that a hotspot producing a 5 mu Sv/h dose at a distance of 3 m can be imaged every 10 s, with angular resolution better than 10 degrees (FWHM). The 3D position sensitive scintillators and thin monolithic MPPC arrays are the key technologies developed here. By measuring the pulse height ratio of MPPC-arrays coupled at both ends of a Ce:GAGG scintillator block, the depth of interaction (DOI) is obtained for incident gamma rays as well as the usual 2D positions, with accuracy better than 2 mm. By using two identical 10 mm cubic Ce:GAGG scintillators as a scatterer and an absorber, we confirmed that the 3D configuration works well as a high resolution gamma camera, and also works as spectrometer achieving typical energy resolution of 9.8% (FWHM) for 662 keV gamma rays. We present the current status of the prototype camera (weighting 1.5 kg and measuring 8.5 x 14 x 16 cm(3) in size) being fabricated by Hamamatsu Photonics K. K. Although the camera still operates in non-DOI mode, angular resolution as high as 14 degrees (FWHM) was achieved with an integration time of 30s for the assumed hotspot described above. (C) 2013 Elsevier B.V. All tights reserved.