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Low-noise cryogenic preamplifiers for semiconductor X-ray detectors will be described. The basic structure of field-effect transistor (FET) preamplifier and its major parameters in the context of the X-ray spectrometer will be presented. Operational characteristics of an FET and its noise properties, especially at cryogenic temperatures, will be outlined. Noise frequency response requiring band-pass limitations and their achievement through pulse shaping in the main amplifier will be described. Noise formulation will be presented emphasizing the influence of various parameters and the conflicting requirements of low-noise and high count-rate performance. Various feedback schemes will be described, comparing in particular the noise and count-rate characteristics of the opto-electronic and the resistive feedback configurations. Recent experimental results with silicon and germanium spectrometers will be given and compared with the theoretical limitations. Finally, future possibilities in the development of X-ray energy analyzers will be assessed.
semiconductor devices, spectrometers, silicon, germanium, X-ray spectra, X-ray analysis, electromagnetic noise, cryogenics, preamplifiers, solid state counters, dispersing, energy methods
Senior physicist, ORTEC, Inc., Oak Ridge, Tenn.