Cryogenic UV-photomultipliers for Gamma-camera

The interaction of radiation with liquid xenon (LXe), inducing both scintillation and ionization signals, is of particular interest for gamma-induced Compton-sequences reconstruction. We have been collaborating with Ecole des Mines – Nantes on the development of a Compton Camera based on a LXe time-projection chamber (TPC) - dedicated to a novel ''3γ imaging'' technique. The goal has been to improve radiation imaging by combining PET & Compton Cameras. The basic idea was to replace standard vacuum PMTs by a large-area Gaseous Photomultiplier (GPM), for recording the LXe scintillation photons. Different UV-sensitive GPM concepts were materialized on small prototypes operated in cryogenic conditions. Among them cascaded Thick Gas Electron Multipliers (THGEM), having a CsI photocathode deposited on the first THGEM electrode, and cascaded THGEM/PIM/Micromegas GPM. The operation of a 100mm diameter cryogenic imaging-GPM concept has been recently demonstrated in my group (see paragraph on “basic research”).