Low-Noise Preamplifier for High Count Rates

A low-noise charge sensitive preamplifier employing charge restoration after each detector pulse is described. Charge restoration is performed for each pulse by exposing the input FET to an optical flash (produced by a GaAs diode) proportional to the amplitude of the main amplifier output pulse. Special care has been taken to eliminate temperature and linearity problems of the GaAs diode. This preamplifier is capable of operating at very high "energy rates", e.q. for 5 MeV radiation at more than 100,000 cps.