A depth-encoding anger detector using scintillating fibers

Parallax error during coincidence imaging with dual-head cameras causes inf idelity in tomographic images, worsening as one increases crystal thickness to combat poor detection efficiency. We are integrating wavelength-shiftin g (WLS) scintillating fibers onto a thick NaI(Tl) crystal to create an Ange r detector capable of measuring depth-of-interaction (DOI). Our studies tar get eventual implementation on the large-area detectors of commercial multi head coincidence imaging systems. The prototype detector uses a 127 x 127 x 25.4 mm(3) NaI(Tl) crystal. The crystal is sealed in a two-windowed alumin um enclosure-both faces of the crystal are coupled optically to glass windo ws. A ribbon of 125 square 1-min WLS fibers is coupled lengthwise to the en trance window; enhanced-green-response photomultiplier tubes (PMTs) detect the light from the fibers. The number of fibers exhibiting signals above a threshold value determines the DOI. For interactions near the ribbon, light localizes in only a few fibers; light from distant interactions illuminate s many fibers. Four PMTs, for position centroid calculation and energy wind owing, are coupled through a light-guide to the exit window of the detector . This paper summarizes the concept of the depth-encoding Anger detector, d escribes the design of the detector prototype, and details on-going feasibi lity testing and optimization of the detector.