Prototype of Field Waveform Digitizer for BaF2Detector Array at CSNS-WNS

Abstract

At the China spallation neutron source-white neutron sources (CSNS-WNS), the BaF2 (barium fluoride) detector array in planning is designed for neutron capture cross section measurements with high accuracy and efficiency. Once proton beam collides with the spallation target, the neutrons will fly from the target to specimen surrounded by BaF2 array and produce cascaded $\gamma $ rays eventually. The time of flight (TOF) corresponds to the neutron energy. To identify $\gamma $ signals from the high $\alpha $ -particle background, pulse shape discrimination (PSD) technique is usually used according to the ratio of fast to slow component in the signal. Waveform digitization is a valid supporting technology for PSD. In order to precisely obtain the wave and time information carried by detector signal, and to maximally cover the signal dynamic range, a universal digitizer with 1 GSps sampling rate and 12-b resolution has been designed based on a 3U PXIe platform in this paper. Besides waveform digitization, this customized digitizer also measures TOF precisely based on the digitized waveform data and technique of time-to-digital converting on field-programming gate array. Test results show that this digitizer can achieve good static and dynamic performance. The specification of effective number of bits is better than 9.43 b within 198 MHz. Digitizer proposed in this paper can meet the requirements for BaF2 spectrum at CSNS-WNS.