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 ga mma ray sources. This instrument includes both a conventional video ca mera and a gamma ray imaging system, which is based upon a position se nsitive 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 te sts to image radioactive sources with gamma ray energies between 120 k eV and 2.4 MeV. At 662 keV, this new system achieves an angular resolu tion of 4 degrees FWHM with an absolute efficiency of 1x10(-6) at 1 me ter, with sensitivity such that a 0.5 mCi Cs-137 source at 5 meters ca n be located in <60 seconds. Higher efficiency and sensitivity can be achieved at lower spatial resolution.