The long-term stability of the DSPEC PLUS spectrometer at the Reactor Institute Delft

In the 1990s, digital spectrometry became feasible as very fast ADCs became available. In a digital spectrometer, the signal from the detector is no longer shaped by analog circuitry before it is handed over to the ADC that determines the channel number-it is digitized to begin with. High count rates that vary within the acquisition time are dealt with satisfactory in these spectrometers. The gain of analog amplifiers is known to be temperature sensitive. Digital spectrometers supposedly do not exhibit such sensitivity. In general, very high gain stability is expected because of this. Stability tests of a DSPEC(PLUS) digital spectrometer were performed at Ortec over a period of seven months. Also, the performance of such a digital spectrometer was monitored during seven years in the reactor containment building of the Delft research reactor--where no climate control is present. It is concluded that the long term gain stability of the digital systems tested is about 0.2%--almost as good as the 0.1% of the analog system used before. The FWHMs as observed are quite a bit better with the digital spectrometer.