Construction of a Wide-Range Gamma-Ray Spectrometer

Full text: Broad-range detectors feature the useful energy range of 4 to 3000 keV. To calculate the peak areas in this region reliably the spectrum must be measured in the energy range from at least 3 to 3000 keV. It is not possible to cover the useful energy range of such a detector with one spectrum since the dynamic range of commercially available ADC converters is only about 500. To cover a wider energy range a Canberra 8172 Wilkinson-type ADC was operated with the lower level discriminator set very close to the noise level. To avoid registration of pulses belonging to excursions in the noise of the spectrometer a low-energy filter (ref 1), preventing the registration of pulses with slow rise times, was used. The closeness of the noise level to the level set by the lover-level discriminator disturbed the measurement of the live time of the spectrometer therefore the pulser method was used to measure the counting losses. The efficiency of the low-energy filter was 95% at 6 keV and 80% at 4 keV. At low count rates the counting losses measured by the pulser method were approximately10%. (author)