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.