A fully digital coincidence Doppler broadening spectrometer based on FPGA

Abstract

In this article, we implemented a fully digital Coincidence Doppler Broadening (CDB) spectrometer consisting of two HPGe detectors, a fully digital processing and acquisition board, and a dedicated software system. The Field Programmable Gate Array (FPGA) on the board extracts energy and time stamp of digitized pulses from HPGe detectors, and communicates with the dedicated software by which the single channel spectrums and 2D coincidence spectrum were produced. We designed an instruction set dedicated to the CDB Spectrometer and the controller module in FPGA so that the FPGA subsystem is fully controllable and configurable. The trapezoidal pulse shaping algorithm was implemented in FPGA whose arguments are all configurable through the dedicated software by the instruction set. We examined the long-term stability of the spectrometer by 511 keV peak position of both channels. The 2D Gaussian fitting is performed on coincidence spectrum by the software to correct the peak drift of both channels. The results show that this method effectively improves the Doppler-broadened spectrum, by which the peak-to-background ratio increases from 7.0 × 105 to 1.9 × 106.