Semiconductor x-ray spectrometer system type 454.

The semiconductor detector X-ray spectrometer type 454 provides a resolution of 220 eV FWHM for the Fe Kα X-ray line at count rates up to 10 4 pulses per second, and is suitable for the energy range 4 to 60 keV. The preamplifier uses the pulsed optical feedback technique and a remounted input field effect transistor which operates at 130 K. The detectors are fabricated from commercially available hyper-pure n-type silicon and do not suffer from the carrier trapping effects exhibited by some lithium drift compensated silicon detectors at temperatures approaching 77 K. The high initial cost of this material is offset by savings in manufacturing time and in the cost of the sophisticated equipment required for lithium drift compensation of p-type silicon. Drifting times of possibly weeks coupled with uncertainty about the qualities of the final product make the more costly hyper-pure n-type silicon an attractive proposition for small laboratories. The doping density is stable and is not affected appreciably by the high temperature (300ºC) processing required to diffuse lithium into one surface and so produce a highly doped low sheet resistivity n contact. Guarding the n+ contact ensures a signal contact leakage current of less than 0.01 pA when the 5-8 mm thick detector is fully depleted