A novel imaging technique based on the tridimensional localization of a (beta, gamma) radioisotope emitter with a liquid-xenon Compton telescope was proposed at SUBATECH in 2003. This technique named 3 gamma imaging combines a classical positron emission tomography device and a Compton telescope for the reconstruction of two back-to-back annihilation gamma-rays and the third one respectively. The interaction of the last one with liquid-xenon induces a scintillation signal read by a vacuum photomultiplier tube to trigger the acquisition of the simultaneous ionization signal read by a MICROMEGAS (MICRO MEsh GAseous Structure) which allows the measurement of each interaction position and corresponding energy. In this experimental framework, we propose an original way of scintillation reading, replacing the traditionnal photomultiplier tubes devices by a large-area cryogenic gaseous photomultiplier. This photodetector consists of a reflective solid cesium iodide photocathode for the photoconversion of UV light and a combination of three micro-pattern gaseous detectors : the THGEM (THick Gaseous Electron Multiplier), the MICROMEGAS and the PIM (Parallel Ionization Multiplier). It should allow a virtual segmentation of the liquid xenon volume to reduce the telescope occupancy. First results obtained with a small area prototype at liquid xenon temperature (173 K) are presented.
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