A three dimensionally position sensitive large area detector

A large area detector consisting of a parallel plate avalanche counter (PPAC) and a trapezohedral ionization chamber (TIC) is described. Its active area is 184 cm². The time resolution of the PPAC is 175 ps. The energy resolution of the TIC is 0.4%, the energy loss resolution 2.8%, the nuclear charge resolution 2.3%. The TIC is position sensitive in three dimensions. The position x is measured via a saw-tooth anode with a resolution of 0.7 mm; the drift time coordinate shows a resolution of δy ? mm. The range z is determined by a new technique, a graded density Frisch grid. It enlarges the dynamic range of the charge measurement down to the Bragg maximum at E/A ～ 1 MeV. The resolution is δZ/Z ? 3.5%