Design for a Versatile Charge Sensitive Preamplifier for Nuclear Radiation Detectors

The design of the high-gain, low-noise, charge-sensitive preamplifier discussed in this paper was prompted by the need for a unit that would fulfill many experimental requirements without modification and/or redesign. This transistorized preamplifier has good versatility without sacrificing performance characteristics. The maximum gain is about 650 volts/picocoulomb, but can be reduced by a factor of 1200. The noise figure is approximately 300 rms electrons (2.6 keV fwhm referred to a silicon detector) at zero input capacitance and 1-μs pulse shaping. Either polarity input signal is accepted, with a maximum output of either plus or minus 5 volts delivered to a 50-ohm load with better than 0.05% linearity. When desired, 1-μs integration and differentiation can be switch-selected to provide shaped pulses suitable for scalers or pulse height analyzers. Circuit design considerations to include frequency compensation, linearity, temperature stability, and bipolar operation are discussed. Graphs indicate preamplifier noise and risetime performance characteristics. A brief analysis describes charge-loop performance in terms of circuit parameters. A modified version of the preamplifier, which has provisions for removing the FET from the chassis and cooling it to about 130°K, has yielded a zero-input-c apacitance noise figure of approximately 140 rms electrons (0.95 keV germanium).