Large-Area Compton Camera for High-Speed and 3-D Imaging

Abstract

Compton imaging is a promising imaging modality for radioactive contamination in nuclear facilities. However, most of the Compton cameras in nuclear applications have been constructed with small detector sensors, up to a few centimeters, resulting in low imaging sensitivities. To overcome the limitation and improve imaging sensitivity, in this paper, a Compton camera, named a large-area Compton camera (LACC), was developed using two large-size (27 cm $\times27$ cm) monolithic NaI(Tl) scintillators and 72 square-type photomultiplier tubes. The imaging performance of the LACC was evaluated for surface and internal contamination cases. Our results show that the absolute imaging sensitivity of the LACC was $3.4\times 10^{-5}$ for a 137Cs point source at about 1-m distance in front of the LACC, which is a few $10\times $ higher than those of the existing Compton cameras. The obtained imaging resolution was 14.1° full-width at half-maximum (FWHM) when we use the backprojection algorithm and 5.6° FWHM when we use the maximum-likelihood expectation–maximization algorithm. The LACC also showed the 3-D imaging capability, not only for the surface contamination cases but also for the internal contamination cases within a depth of a few tens of centimeters.