Coincidence time resolution investigation of BaF₂-based H6610 detectors for a digital positron annihilation lifetime spectrometer

Abstract

BaF 2 -based detectors have been used in many fields requiring fast timing, especially in positron annihilation lifetime (PAL) spectroscopy. The performance of a PAL spectrometer is closely correlated with the time response of BaF 2 -based detectors. Therefore, it is important to select scintillation detectors with excellent time resolution. In this work, the coincidence time resolution of BaF 2 -based H6610 detectors was investigated using a digital oscilloscope. The time response of detectors has been optimized by tuning the supply voltages, the sampling rate of the oscilloscope, and digital fraction constants, achieving a conicidence time resolution of about 162 ps for the 0.511 MeV annihilation γ-ray pairs and 108 ps for the 60 Co cascade γ-rays, respectively. Furthermore, a digital PAL spectrometer composed of two BaF 2 -based H6610 detectors and an oscilloscope was developed with a time resolution of around 130 ps, much better than most digital PAL spectrometers.

Study of timing performance parameters for a SiPM-based digital positron annihilation lifetime spectrometer

“…Through the timing resolution measurements, we confirmed that the timing resolution of the SiPM-based digital PAL spectrometer was different according to the γ-ray energy. The higher the γ-ray energy the better the timing resolution, which well matched the results of previous studies [5,10]. The output pulse of the SiPM is the sum of individual pulses from micro cells so the slope of the pulse is proportional to the number of fired micro cells.…”

“…Digital constant fraction discrimination (dCFD) is the most common time pick-off method for measuring the arrival time of the γ-ray in scintillator detectors such as the PAL spectrometer and positron emission tomography (PET) detectors [5,7,14,19]. The principle of dCFD is to determine the arrival time of radiation when the pulse amplitude reaches a specific threshold fraction of the maximum amplitude as shown in figure 2.…”

“…With the development of technology, several digital PAL spectrometers using fast oscilloscope or digitizer have been developed to replace nuclear instrumentation modules (NIM modules) such as the constant fraction discriminator (CFD) and the time-to-amplitude converter (TAC) [4][5][6][7]. In addition, recent studies developed a silicon photomultiplier (SiPM) based PAL spectrometer that has many advantages over the conventional PAL spectrometer, which is configured with PMT [8,9].…”

“…Despite the difference in the energy of the start signal and stop signal when the lifetime of a positron is measured, it is not considered in most cases of PAL measurement. Only a few studies have considered the difference in the timing resolution according to the γ-rays energy [5,10].…”

A new system for real-time data acquisition and pulse parameterization for digital positron annihilation lifetime spectrometers with high repetition rates

“…Groups in Japan [17,18] and Finland [19,20] recorded the first fully-digital lifetime spectra based on fast digital oscilloscopes. In the following years, many other laboratories [21][22][23][24][25][26] performed a transition from analogue to digital technology. The advantages of digital data acquisition became increasingly visible.…”