Development of a compton imager based on scintillator bars

We are developing a compact, rugged Compton-scatter gamma-ray imager with a large field of view and a low channel count for use in investigations involving radioactive threat material. The two detector planes, (scatterer and absorber), employ bars of NaI(Tl) read out by photomultiplier tubes (PMTs) located at each end. The position of interaction along the bar is reconstructed from the relative pulse heights of the PMTs. We present the imaging performance of a reduced-scale prototype using three bars in the scatter layer and three bars in the absorber layer. A 100 µCi 662 keV source located 180 cm away from the detector is well localized to within 2° with 60 s of data over 90% of the time.