The CSPD-2 gamma-ray imaging system

A compact portable γ-ray vision system consisting of a lead multi-hole collimator, CsI(Tl)/photodiode detector array, CCD camera and personal computer, has been constructed and tested. The optical picture obtained with a CCD camera is overlaid with γ-ray intensity distributions at different energies to enable immediate localization of multiple radioactive sources. The γ-ray detector employs a shielded array of sixteen 1×1×3 cm CsI(Tl) scintillation crystals, each of which is viewed by a 1 cm square Hamamatsu PIN silicon photodiode. The device operates in the energy range from 100 keV to 3 MeV with an average energy resolution of about 7% FWHM, and angular resolution of about 40 FWHM at 662 keV. The collected γ-ray distribution is processed using a maximum-likelihood algorithm to provide a more precise reconstruction of the γ-emitter distribution. The detector system is mounted on a pan-and-tilt table; the total weight of the imaging system is about 30 kg. The performance of this instrument has been tested in our laboratory and the results show that this system should be a competitive candidate for radiation monitoring in nuclear facilities