8-layer DOI encoding of 3-dimensional crystal array

An 8-layer depth of interaction (DOI) detector was designed on the basis of the technique we have developed for 4-layer DOI detectors. It attains 8-layer encoding by pulse shape discrimination (2-layer DOI encoding) and the proper reflector arrangement in a 3-dimensional crystal array (4-layer DOI encoding). Its capability was proved with an 8 layers of 10times10 Gd₂SiO₅ (GSO) crystal array coupled to a 256-channel flat panel position sensitive photomultiplier tube (256ch FP-PMT). The dimensions of a crystal element are 2.90 mmtimes2.90 mmtimes3.75 mm and intervals of 16times16 multi anodes in the 256ch FP-PMT are 3.04 mm. Two kinds of GSO were used to make pulse shape discrimination; GSOs of 0.5 mol% and 1.5 mol% Ce dopants that show 60 ns and 35 ns scintillation decay times, respectively. In the crystal array, the layer-1, the farthest from the 256ch FP-PMT, layer-3, -5 and -7 were composed of 0.5 mol% GSO:Ce crystals and 1.5 mol% GSO: Ce crystals were in other layers. Performance of the 8-layer DOI detector was evaluated by irradiating 662 keV uniform gamma-rays. The results indicate capability of 8-layer DOI encoding. To prove the validity of the layer encoding, fan-beam of 662 keV gamma-rays are irradiated onto the side face of each layer. The obtained 2D histograms show the right structure in each corresponding layer clearly. In this measurement, the pulse height distribution of a central crystal in each layer suggests the minimum light output of 0.62 to the maximum and about 15% energy resolutions for all layers