A large area RICH photon detector for astrophysics

We have developed a detector of 1.5 × 1.4 m2 area which measures individual photons with a spatial resolution of ∼1 cm. This device is in the focal plane of a 3 m long gas-filled Ring Imaging CHerenkov (RICH) instrument designed to make precision measurements of the velocity of high energy cosmic rays at the top of the atmosphere. In future applications this type of detector may be combined with a magnet spectrometer to make mass measurements of cosmic rays at high energy. The detector is a wire chamber filled with an ethane/TMAE mixture having fused silica windows. The signals are collected by 18 432 cathode pads of 1 cm2 area connected to a VLSI electronic readout system. The quantum efficiency of the detector in the wavelength region of 180–200 nm is ∼12%. We shall discuss the design and operation of this detector.