Design of a Time Discriminator in a Low-background, Anti- Compton Spectrometer

Abstract

Abstract Compton scattering leads to the incomplete deposition of particle energy and produces a Compton scattering background, which decreases the measurement accuracy of low-energy rays. The low-background, anti-Compton spectrometer outputs 7-channel time signals through coincidence detector. The Compton events can be identified and reduced by the inverse coincidence of these time signals with the energy signals coming from the High Purity Germanium (HPGe) Detector. The precise-time measurement circuit can pulse shape the signal from the coincidence detector and accurately draw the arrival time of the signal. This is the key for a low-background, Compton-suppressed spectrometer to realize accurate anticoincidence measurements. In this study, a constant fraction discriminator (CFD) circuit was designed to replace the traditional leading-edge timer. A constant fraction discriminator-based all-pass filter without a delay line was used as the delay module. The advantages of the proposed method include the integration of circuits, low power consumption, and low cost. The simulation nuclear signals with different amplitudes, which were measured using the proposed CFD design, were outputted using the signal generator. The maximum deviation of the circuit triggering ratio was 2.5% and time jitter was 1.6 ns. The anti-Compton spectrometer with constant fraction discriminator has good Compton suppression effect. The peak-to-Compton ratio of the Compton-suppressed spectra is 1333:1 and the Compton-suppressed coefficient is 6.3.