Position-sensitive NaI(TL) detector module for large-area Compton camera

In the present study, we developed a position-sensitive NaI(Tl) scintillation detector module for use in the development of a large-area Compton camera. The developed detector module employs a large ( i.e. , 27 × 27 × 2 cm 3 ) monolithic NaI(Tl) scintillator coupled with a closely packed array of 6 × 6 square PMTs. A multiplexer-based signal processing circuit and a data acquisition system were developed to estimate the interaction position in the scintillator from the signals of the PMTs by using the maximum likelihood position estimation algorithm (MLPE). The performance of the developed detector was evaluated experimentally, showing that the energy and the time resolution of the detector are 7.88% (for 662-keV gamma ray) and 9.6 ns FWHM, respectively, which are comparable to those of a commercial three-inch cylindrical NaI(Tl) scintillation detector. In addition, the spatial resolutions were about 3-to-6-mm FWHM for a wide energy range (59.5 - 1173 keV) and various interaction positions on the detector (from center to edge), which are satisfactory results considering that a 3-mm-diameter collimated gamma-ray beam was used in the experiments.