Study of low cost continuous Gd2O2S:Pr powder scintillator screens in photon counting mode using a dedicated small nuclear imaging camera

The aim of this study is to propose and evaluate a low cost alternative solution as a detector module in nuclear imaging. For this purpose, we have assessed the performance of Gd₂O₂S:Pr powder scintillator in the form of thick screens easily produced in our laboratory. All measurements were carried out in photon counting mode using ^m99Tc. To our knowledge, Gd₂O₂S:Pr powder phosphor screens have never been used in nuclear imaging. Evaluation was performed using a small field of view gamma camera. A general purpose collimator and a position sensitive photomultiplier tube R9232 were used. Different samples with coating thickness varying from 100 mg/cm² to 1.2 g/cm² were tested. The procedures for optimizing the thickness of the screen and PSPMT configuration together with quick and optimal amplification of 4 signals (Xa, Xb, Yc, Yd) are reported. The more efficient coating thickness of 600 mg/cm² which corresponds to ~2mm thickness in height was found to be experimentally optimum. Sensitivity and spatial resolution were measured and compared to two standard 3 × 3 × 5 mm³ and 2 × 2 x3 mm³ discrete CsI:Tl scintillator arrays under the same conditions. The measurements showed significant improvements in detector spatial resolution (up a factor of 1.2 compared with 2×2 CsI) but loss of efficiency (4 times compared with 2×2 CsI) when a 2 mm thick Gd₂O₂S:Pr powder scintillator was used. Moreover, system performance with the proposed screen in terms of energy resolution and uniformity response is reported.