An imaging nuclear survey system

A combined video and gamma ray imaging system has been developed which can rapidly determine the location, distribution, and intensity of gamma ray sources. This instrument includes both a conventional video camera and a gamma ray imaging system, which is based upon a position sensitive photomultiplier tube, a scintillator, and a pinhole collimator. The gamma camera records the position and energy of each interaction, determining the energy spectrum and count rate from each direction. We have used a prototype of such an instrument in preliminary field tests to image radioactive sources with gamma ray energies between 120 keV and 2.4 MeV. At 662 keV, this new system achieves an angular resolution of 4° FWHM with an absolute efficiency of 1×10^-6 at 1 meter, with sensitivity such that a 0.5 mCi ¹³⁷Cs source at 5 meters can be located in <60 seconds. Higher efficiency and sensitivity can be achieved at lower spatial resolution