Simple charge division readouts for imaging scintillator arrays using a multi-channel PMT

Three simple charge division circuits were assembled, and tested, as 2-D readouts for multi-channel photomultiplier tubes (MC-PMT). They were evaluated with an 8×8 array of individual scintillators (2×2×10 mm BGO) coupled to a 64 channel MC-PMT (Philips XP1722) via 25 cm long, 2 mm diameter, double clad, optical fibers (Kuraray). This type of γ-ray imaging detector has many potential applications in medical and industrial imaging. Independent channel readout allows for the discrimination of scatter within the array, and higher count rates, but it requires an excessive amount of supporting electronics. This is specially true for multi-array imaging systems with hundreds, or thousands, of channels. In this study, the number of channels being read out was reduced from 64 to 4. This was achieved by the use of simple resistor networks which take advantage of the discretized nature of the scintillator array, the low crosstalk of the MC-PMT and low input impedance current-sensitive preamplifiers. For each circuit, the scintillator identification accuracy was compared. The identification accuracy as a function of deposited energy was also determined by exposure to various γ emitters. It was found that the preamplifiers circuit noise contributed the most to the degradation of the detector's spatial response so several low noise op amps were evaluated. It was also determined that keeping the preamplifiers input impedance small was necessary for accurate positioning. The timing resolution of the detector was slightly degraded by the readout circuit.