A simplified spectrometer based on a fast digital oscilloscope for the measurement of high energy γ-rays

A simplified digital spectrometer for studying γ-rays with energies up to ~100MeV is presented and tested. The spectrometer only consisted of a fast digital oscilloscope and three scintillation detectors which can work in single or in coincidence modes: two BGO-detectors comprising ∅7.62×7.62cm BGO-crystals and one plastic detector which includes an organic polystyrene-based scintillator. The basic properties of the spectrometer (energy resolution, time resolution, γ-rays detection efficiency) were studied exhaustively also using Geant4-based Monte-Carlo simulation. Several numerical algorithms for processing of waveforms in offline mode were proposed and tested to perform digital timing, pulse area measurement and correction of pile-up events without rejection. As a result, the energy resolution of the spectrometer was up to 10% better than that was obtained by a common 10-bit CAMAC ADC with the same detectors. Furthermore, the pile-up processing algorithm based on the pulse shape analysis showed high efficiency under severe conditions (the portion of pile-up events was ~30%). The measured maximum acquisition rate of the spectrometer was 1.8×105waveforms/s.