D. Marocco

A digital data acquisition system optimized for spectrometry with liquid scintillation detectors

The prototype of a new concept FPGA-based digital acquisition board has been developed for application with scintillation detectors. The board performs digitisation of pulses at 200 MSamples/s with 14-bit resolution. A Dynamic Windows Data Acquisition (DWDA) method is used such that data sampling occurs only when pulses are present and for a time window depending on the width of each pulse. This allows to reduce the amount of stored data and, at the same time, to handle count rates up to the MHz range. Peak identification, baseline correction, pile-up removal, neutron/� ray separation and pulse height analysis are performed by means of a LabVIEW TM program. We show the results of measurements carried out with an NE213 liquid scintillation detector at the PTB (Physikalisch-Technische Bundesanstalt) accelerator facility in Braunschweig (Germany) both with 2.5 MeV and 14 MeV neutrons. The measurements have been performed at different source to detector distances as well as various detection angles. In the digital branch of the acquisition, the pulses have been stored on disk and analysed after the experiment. The comparison between the PTB standard analogue pulse processing system and the new digital system is presented and discussed, in particular in terms of energy resolution, dependence of the pulse height spectra on different total count rates, system stability with time, pile-up rejection and neutron/� -ray separation capability.