Development of HPDs for applications in physics and medical imaging

We discuss the design, construction and first results of two Hybrid Photon Detectors (HPDs) under development for applications in neutrino physics and Positron Emission Tomography (PET). The concept of a large almost spherical HPD is being developed as instrumentation for a next generation underwater Cherenkov detector array. Its main advantages compared to a conventional hemispherical PMT are the considerably increased viewing angle, minimum transit time spread, high gain stability and immunity to the Earth's magnetic field, intrinsic to the design. A proximity focused ceramic HPD with a flat sapphire entrance window has been developed in the framework of a conceptual design study of a novel 3D Axial PET scanner. The PET–HPD is equipped with custom-designed fast front-end electronics, allowing sequential and sparse mode readout of its 208 pads. Prototypes of both HPDs are being built in a dedicated vacuum deposition facility at CERN.