Reconfigurable positron annihilation lifetime spectrometer utilizing a multi-channel digitizer

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A: Positron Annihilation Lifetime (PAL) spectroscopyis widely applied in material and biomedical science. The conventional analog PAL spectrometer built by multiple Nuclear Instrumentation Modules gradually shows deficiencies in performance. Most digital PAL spectrometers strongly rely on the advanced Analog-to-Digital Converter (ADC) or oscilloscope with an ultrahigh-speed sampling rate. In this paper, we developed a prototype system of the digital PAL spectrometer based on ordinary Time-to-Digital Converter (TDC) and ADC. Benefiting from the high-performance digitization devices and digital signal processing algorithms accomplished by Field-Programmable Gate Array (FPGA), the system achieves remarkable energy and lifetime resolution in a simple structure and at a much lower cost. Electronic test results show that the time resolution of the TDC reaches 67 ps and the Effective Number Of Bits of ADC is better than 10.77 bit. The energy resolution of 511 keV photopeak is 4.1% and the Full Width at Half Maximum of the lifetime spectrum reaches 210.6 ps when using Hamamatsu H3378-50 Photomultiplier Tubes with LaBr 3 :5% Ce 3+ scintillators as detectors.

Section: Pal Spectra Testsmentioning

confidence: 95%

Development of a TDC-based digital positron annihilation lifetime spectrometer

Ge¹,

Xue²,

Cong³

et al. 2020

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“…The range between 511 and 1275 keV photopeaks is included. Then we use software to set the energy windows for start and stop signals [13]. As we know, start signals of coincidence events come from the 1275 keV nuclear photons (emitted almost simultaneously with the positrons), while stop signals come from the 511 keV annihilation photons.…”

Section: Spectrometer Designmentioning

confidence: 99%

“…The simulated PAL spectra are created by LabVIEW random value generators (exponential, normal, and uniform distribution) according to the mathematical model of PAL spectra [1,18] and should be "perfect" without any distortion. But we can distort the spectra by adding kinds of "incorrect" coincidence events [13], or adjusting the time resolution function and its FWHM (full width at half maximum), zero-channel position, channel width, background rate, and so on. In experiments, the two sub-spectra (conventional and inverse) may have different parameter values, so the combined spectrum would be distorted even if the sub-spectra are "perfect".…”

Section: Symmetrical Pal Spectra Simulationsmentioning

confidence: 99%

See 1 more Smart Citation

Symmetrical positron annihilation lifetime spectrometer and single-sided measurements

Cong¹,

Gu²,

Han³

et al. 2019

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A: Positron annihilation lifetime (PAL) spectroscopy is a useful tool in material defect studies. In this work, a symmetrical PAL spectrometer was developed based on a conventional system and 22 Na radioactive source. Both detectors provide start and stop signals to double the counting rate without adding devices. Zero-channel position is calibrated automatically during the measurement to combine the two sub-spectra, which can be applied to larger systems with more detectors. The differences of zero-channel positions and time resolutions of two sub-spectra were simulated to confirm the feasibility of our work. Then we used polyimide film (Kapton film, the packaging material of 22 Na source) as reference sample to collect PAL spectra with only one piece of tested sample (single-sided). The influences of high and unknown intensity of source components were simulated to check the importance of enough counts and accurate source correction. Symmetrical PAL spectrometer provides higher counting rate to meet the requirement of single-sided sample. Experimental results confirmed that our PAL spectrometer performs well for both double-sided and single-sided measurements.

“…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].…”

Section: Introductionmentioning

confidence: 99%

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

Choi¹,

Ko²,

Kim³

et al. 2022

Positron annihilation lifetime spectroscopy (PALS) is a popular method for studying defects in materials. With the development of fast digital oscilloscopes and digitizers, the conventional analog positron annihilation lifetime (PAL) spectrometer is being replaced by a digital PAL spectrometer. Recently, newly conducted research has developed a PAL spectrometer using a silicon photomultiplier (SiPM) instead of a photomultiplier tube (PMT). Timing resolution of PAL spectrometer needs to be improved to identify the lifetimes of positrons. Many parameters affect the timing performance of a SiPM-based digital PAL spectrometer: bias voltage, pulse smoothing, and the constant fraction value of digital constant fraction discrimination (dCFD). Timing resolution depends on the radiation energy, but only a few studies have considered the energy difference of 1274 keV and 511 keV. In this study, we optimized the timing performance parameters of the SiPM-based digital PAL spectrometer by conducting the timing resolution measurements using two γ-ray sources (22Na and 60Co). With a 32 V bias voltage, 5th degree polynomial fitting method, and optimal constant fraction value, we optimized the timing resolution of our SiPM-based digital PAL spectrometer. Furthermore, the optimal constant fraction value depended on the γ-ray energy and we verified it by timing resolution measurement using 207Bi. We studied the reason why performance parameters have optimal conditions and the optimal constant fraction value varies depending on the γ-ray energy. With optimized performance parameters, we measured the lifetime spectrum of pure silicon to confirm the SiPM-based digital PAL spectrometer. The timing resolution function of the SiPM-based digital PAL spectrometer was 185.6 ps.