Lifetime Spectrometer Research Articles

Record high counting rate of positron annihilation lifetime spectrometer achieved by [formula omitted] coincidence

Conventional positron annihilation lifetime (PAL) spectrometers, which employ the γ-γ coincidence with two perpendicularly-positioned detectors, have a typical counting rate of 100–300 counts per second (cps). To increase the counting rate, according to the optimized structural parameters using Geant4 simulation, a 22Na positron source (∼ 1.665 MBq), a silicon photomultiplier (SiPM), and digital waveform technology are utilized for the first time to a β+-γ coincidence PAL spectrometer. After the optimization and verification of accuracy and stability, this spectrometer can achieve a time resolution of about 206 ps, and a record high effective counting rate of approximately 19000 cps (∼ 11000 cps/MBq), which is two orders of magnitude greater than those of conventional PAL spectrometers. The significant shortening of measurement time for a single PAL spectrum enables us to observe sub-minute-scale evolution of microstructure during rapid physical and chemical processes in the future.

Investigating the properties of ortho-positronium in liquid scintillators under oxygen quenching

Investigating the mechanism of positron annihilation in liquid-scintillator based neutrino experiments could be helpful for positron reconstruction algorithms and positron-electron discrimination analysis. Based on this, we utilize a novel positron annihilation lifetime spectrometer to characterize a series of liquid scintillator samples without direct contact with the positron source by applying the anti-coincidence method, which facilitates the measurement of liquids with high accuracy and low background. We obtain an ortho-positronium (o-Ps) lifetime value of 3.02 ns for liquid scintillators composed of linear alkylbenzene and two solutes, and we also measure liquid scintillator samples by bubbling different gases to study the interaction of oxygen dissolved with positronium. The discussion of the annihilation behavior of o-Ps in liquid scintillators further clarify the factors affecting the lifetime and intensity of o-Ps, and the calculation of annihilation rate and free volume radius within the samples has potential applications in characterizing gas solubility and free volume in liquids with o-Ps as probe.

Positron annihilation spectroscopy evaluation of using proton irradiation as a surrogate for early neutron radiation damage

A positron annihilation spectroscopy investigation of early stages of radiation-induced damage in Chinese f/m (ferritic/martensitic) steel SIMP and strengthened variant of f/m steel ODS (oxide dispersion strengthened) EUROFER was conducted. Studied materials were irradiated by neutrons at the LVR-15 research reactor to 0.12 dpa at an average temperature of 260 ± 20 °C, and implanted by protons at the 6 MV Tandetron Accelerator of the Slovak University of Technology, to 0.0196 dpa at room temperature (RT) and 300 °C. The potential of using proton irradiation as a surrogate for early neutron radiation damage was investigated. A lifetime spectrometer and Doppler spectrometer was used to obtain simultaneously positron lifetime (PALS) and Doppler broadening spectra (DBS), which provided experimental data used to characterize the vacancy-type defect and their interaction with H atoms in the studied materials. The obtained results show an increase of mean positron lifetime (MLT) in the proton-implanted samples at RT when compared with high temperature irradiation. Similar trend was observed when comparing vacancy concentration of different irradiation conditions. The impact of temperature on mobility and recombination of defects, as well as effect of vacancy stabilization by H atoms, has been addressed. The effect of ODS microstructure on results has been examined. A methodology of comparing various irradiation conditions has been proposed, where the vacancy concentrations have been normalized by the dpa values. The potential application of proton implantation for evaluation of early stages of neutron damage was found to be promising.

Triple-coincidence positron annihilation lifetime spectrometer based on ultrafast discrimination

In this paper, we establish a triple-coincidence positron annihilation lifetime (PAL) spectrometer based on fast–fast coincidence. It can be used to accurately characterize atomic-scale defects in radioactive samples. The PAL spectrometer consists of three BaF2 detectors and a fast–fast coincidence system, which is composed of analogic electronic modules. The timing resolution of the spectrometer is approximately 198 ps, and the coincidence counting rate can reach 44 s−1 for a 0.9 MBq 22Na source. The results demonstrate that with 22Na activity at 0.9 MBq, the triple-coincidence PAL spectrometer can operate with high precision at 60Co activity levels of up to 4.3 MBq. However, when the activity of 60Co exceeds this threshold, the lifetime spectrum experiences noticeable distortion and an increasing background. As a result, the reliability of the measurement results is compromised. Despite this limitation, the spectrometer was proved successful in characterizing defects in neutron-irradiated RPV steels.

Record high time resolution of positron annihilation lifetime spectrometer achieved by double-stop setup and geometry optimization of scintillators

To precisely characterize the defects in crystalline solids including semiconductors and alloys, it is critical but challenging to improve the time resolution of positron annihilation lifetime (PAL) spectrometers. The effects of geometry and wrapping of scintillators on the time resolution of the PAL spectrometer were studied in detail. Geant4 program simulation was used to clarify the reason why cone-frustum-shaped scintillators have better time resolution than cylinder-shaped scintillators. A figure of merit was proposed to comprehensively evaluate the impacts of the transport and absorption of fluorescent photons on the time resolution of scintillators. Additionally, for the simulations of cone-frustum-shaped scintillators, polished reflective coatings can further improve the time resolution without losing count rate. Eventually, using three cone-frustum-shaped BaF2 scintillators and a double-stop setup, we significantly improved the time resolution of PAL spectrometer to a new record of 88.7 ps, the best time resolution up to date. This enables us to distinguish various vacancy types in crystalline solids more precisely in future.

Positron annihilation study of the reactor pressure vessel model steels irradiated in the high flux reactor

Twelve reactor pressure vessel (RPV) model steels with parametric variation of alloying elements Ni and Mn were characterized by means of positron annihilation spectroscopy before and after irradiation at the High Flux Reactor (HFR) to ∼0.18 dpa at an average temperature of 286 °C. Two independent positron annihilation lifetime spectrometers (PALS) and one coincidence Doppler broadening spectrometer (CDBS), used in the post-irradiation examination, provided a substantial amount of experimental data used to characterize the vacancy-type defects and their agglomerations in the studied materials. The obtained results show an apparent increase in the positron trapping at vacancy-type defects after irradiation, with the concentration of the radiation-induced vacancy-type defects increasing with the Ni and Mn content. The effect of Si and Cu was found to be less pronounced, and the concentration of vacancy-type defects seems to anti-correlate with their content. In addition to open-volume vacancy-type defects, the PALS technique enabled a quantitative estimation of the dislocation-type defects, where only a modest increase in density was observed after the irradiation at the given temperature.

PALSRaM: A three-detector positron annihilation lifetime spectrometer for [formula omitted]-emitting radioactive materials

A three detector positron annihilation lifetime spectrometer for γ-emitting radioactive materials has been constructed and successfully tested. The equipment operates in triple-coincidence mode in order to reject the false coincidence due to the radioactive background generated when dealing with radioactive samples. The spectrometer has been optimized and tested by comparison of the results of well-known material with and without high background radiation. The time resolution of 155 ps is achieved. This paper reports on the design, stability and performance of this new spectrometer.

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

Abstract 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.

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

A Versatile Tetraphenylethene Derivative Bearing Excitation Wavelength Dependent Emission, Multistate Mechanochromism, Reversible Photochromism, and Circularly Polarized Luminescence and Its Applications in Multimodal Anticounterfeiting

A four-channel coincidence digital positron annihilation lifetime spectrometer

Positron annihilation lifetime (PAL) spectrometer is an effective tool to investigate material microstructures. Commonly used PAL spectrometers are conventional PAL spectrometer based on nuclear instrument modules (NIMs) and digital PAL spectrometer based on ultra-high-speed digitizer. Limited by the detection efficiency of the detectors, the coincidence count rate of the PAL spectrometer is always low, causing long time consumption of measurement. To solve this problem, a multi-channel coincidence method based on the ultra-high-speed digitizer was proposed. However, the ultra-high-speed digitizer is usually excessively expensive for research institutes. In this paper, we introduce a four-channel coincidence digital PAL spectrometer. Through the improvement of the timing and trigger circuit, all channels can act as start and stop channels during one measurement. Hence the coincidence count rate can be increased by an order of magnitude. The time measurement shows good linearity and high resolution with a full width half maximum (FWHM) at a level of several tens picoseconds. The effective number of bits (ENOB) of the analog-to-digital converter (ADC) reaches 10.72 bits. The energy resolution of the 511 keV photopeak reaches 4.16% when using LaBr 3: 5% Ce3+ scintillator, better than 4.62% of the conventional spectrometer. The time resolution of our PAL spectra when one channel receives start signals and one channel receives stop signals reaches 193.7 ps, better than that of the conventional spectrometer (212.8 ps). The FWHMs of the lifetime spectra of the two and four channel coincidence measurements are 205.8 ps and 212.4 ps respectively. Moreover, the coincidence count rate of our system increases significantly by using the four-channel coincidence method, which can be 10 times higher than the conventional spectrometer.

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

We present a new system for high repetition rate and real-time pulse analysis implemented at the Monoenergetic Positron Source (MePS) at the superconducting electron LINAC ELBE at Helmholtz-Zentrum Dresden-Rossendorf. Dedicated digital signal processing and optimized algorithms are employed allowing for high bandwidth throughput, online pulse analysis and filtering. Positrons generated from radioisotopes and from bremsstrahlung pair production by means of highly intense accelerator-based positron beams serve as a microstructure probe allowing material characterizations with respect to chemical, mechanical, electrical, and magnetic properties. Positron annihilation lifetime events with up to 13 MHz repetition rate are being processed online without losses while performing signal selections for pile-up reduction, online energy calibration, and — for radioisotope-based measurements — identification of start and stop events.

Boosting the Energy Migration Upconversion through Inter-Shell Energy Transfer in Tb 3+ -Doped Sandwich Structured Nanocrystals

Boosting the Energy Migration Upconversion through Inter-Shell Energy Transfer in Tb ³⁺ -Doped Sandwich Structured Nanocrystals

Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence

Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence

Multiple time-over-threshold readout electronics for fast timing and energy resolving in a SiPM-based positron annihilation lifetime spectrometer

Fast timing and energy resolving capabilities are crucial for a silicon-photomultiplier-based positron annihilation lifetime (SiPM-PAL) spectrometer. Time-over-threshold (ToT) offers an attractive method for combining timing and energy encoding with the advantage of simplicity in electronics implementation and SiPM readout. However, single ToT is not appropriate for a SiPM-PAL spectrometer because of its poor energy linearity and limited energy range. In this work, a multi-ToT readout circuit for a SiPM-PAL spectrometer is developed. Each readout channel uses only a pre-amplifier and a comparator for timing, three comparators for energy resolving, resistors, and capacitors. A simple pulse area estimation method using multi-ToT pulse widths and fixed threshold voltages for energy resolving is presented and evaluated. The energy performance and pulse area integral nonlinearity (INL) are investigated using 22Na, 60Co, and 137Cs γ sources with a SiPM-based scintillation detector. For pulse area spectra using the proposed method, multi-ToT (triple and dual threshold cases) resolves γ energies much better than does single ToT. Using triple-ToT, the pulse area linearity in INL in the energy range of 511–1333 keV is superior than 4.21%, which is at least 25% better than that with dual-ToT. Excellent coincidence resolving times of 161.5 ± 1.4 ps and 162.7 ± 1.3 ps in full width at half maximum are achieved using triple-ToT and dual-ToT, respectively, for 3 mm\\;×\\;3 mm\\;×\\;5 mm lutetium-fine-silicate scintillators. The quantitative energy and timing results show that the multi-ToT circuit is suitable for the readout electronics of a SiPM-PAL spectrometer.

Non‐Stationary Complementary Non‐Uniform Sampling (NOSCO NUS) for Fast Acquisition of Serial 2D NMR Titration Data

AbstractNMR spectroscopy offers unique benefits for ligand binding studies on isotopically labelled target proteins. These benefits include atomic resolution, direct distinction of binding sites and modes, a lowest detectable affinity limit, and function independent setup. Yet, retracing protein signal assignments from apo to holo states to derive exact dissociation constants and chemical shift perturbation amplitudes (for ligand docking and structure‐based optimization) requires lengthy titration series of 2D heteronuclear correlation spectra at variable ligand concentration that may exceed the protein's lifetime and available spectrometer time. We present a novel method to overcome this critical limitation, based on non‐stationary complementary non‐uniform sampling (NOSCO NUS) combined with a robust particle swarm optimization algorithm. We illustrate its potential in two challenging studies with very distinct protein sizes and binding affinities, showing that NOSCO NUS can reduce measurement times by an order of magnitude to make such highly informative NMR titration studies more broadly feasible.

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

BaF2-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 BaF2-based detectors. Therefore, it is important to select scintillation detectors with excellent time resolution. In this work, the coincidence time resolution of BaF2-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 60Co cascade γ-rays, respectively. Furthermore, a digital PAL spectrometer composed of two BaF2-based H6610 detectors and an oscilloscope was developed with a time resolution of around 130 ps, much better than most digital PAL spectrometers.

Preparation of PVA-PFSA-Si pervaporative hybrid membrane and its dehydration performance

In order to ameliorate the trade-off effect in pervaporation process and to reduce the micro-phase separation of hybrid membrane, polyvinyl alcohol (PVA)-perfluorosulfonic acid (PFSA) blending materials were modified by two inorganic components to prepare PVA-PFSA-Si hybrid membrane. PVA-PFSA-Si membrane was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), contact angle measurements, scanning electron microscopy (SEM), positron annihilation lifetime spectrometer (PALS) and swelling measurements. As a second inorganic modifier, the effect of γ-glycidyloxypropyl trimethoxysilane (GPTMS) on the morphology of hybrid membrane was better than that of γ-aminopropyl triethoxysilane (APTEOS). PVA-PFSA-Si/polyacrylonitrile (PAN) composite membrane was used to pervaporatively dehydrate ethyl acetate (EAc)/H2O binary, EAc/ethanol (EtOH)/H2O ternary EAc/acetic acid (HAc)/EtOH/H2O quaternary solutions. At feed temperature of 40 °C, M8 membrane had the permeation fluxes (J) of 262.7, 215.2 and 182.6 g m−2 h−1 and the separation factors (α) of 6673, 3453 and 5374 for pervaporative dehydration of EAc/H2O (98/2, wt%) binary, EAc/EtOH/H2O (96/2/2, wt%) ternary and EAc/HAc/EtOH/H2O (96/1/1/2, wt%) quaternary solutions, respectively. The pervaporative results showed that PVA-PFSA-Si membrane had the excellent dehydration performances for EAc binary or multicomponent aqueous solutions.

Symmetrical positron annihilation lifetime spectrometer and single-sided measurements

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 22Na 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 22Na 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.

A supervised machine learning approach using naive Gaussian Bayes classification for shape-sensitive detector pulse discrimination in positron annihilation lifetime spectroscopy (PALS)

Abstract The acquisition of high-quality and non-artefact afflicted positron lifetime spectra is crucial for a profound analysis, i.e. the correct lifetime spectra decomposition for retrieving the true information. Since the introduction of digital positron lifetime spectrometers, this is generally realized by applying detector pulse discrimination with the help of software-based pulse filtering regarding area and/or shape of the detector pulses. Here, we present a novel approach for shape-sensitive detector pulse discrimination applying supervised machine learning (ML) based on a naive Bayes classification model using a normally distributed likelihood. In general, naive Bayes methods find wide application for many real-world problems such as famously applied for email spam filtering, text categorization or document classification. Their algorithms are relatively simple to implement and, moreover, perform extremely fast compared to more sophisticated methods in training and predicting on high-dimensional datasets, i.e. detector pulses. In this study we show that a remarkable low number of less than 20 labelled training pulses is sufficient to achieve comparable results as of applying physically filtering. Hence, our approach represents a potential alternative.

High quantum yield and well-dispersed quantum dots luminescent composite through sodium carboxymethyl starch.

It is a challenging task to prepare well-dispersed and highly luminescent quantum dots (QDs) powder and a new strategy is reported in this article. Sodium carboxymethyl starch (CMS-Na) was employed in this work to prepare the QDs-starch composite. Ultraviolet (UV) light shows that the blank starches had no fluorescence, while the QDs-starches were highly luminescent. Scanning electron microscopy (SEM) observation shows that the QDs-starch composite has the typical particle morphology with the diameter around 200nm. Energy dispersive X-ray spectroscopy (EDX) results show that there are intensive tellurium (Te) and cadmium (Cd) element signals. Combined fluorescent lifetime and steady-state spectrometer show that the QDs-starch quantum yields (QYs) increase when the QDs loading increases from 1×10-6 mol/g to 2×10-6 mol/g, but when the loadings further increase, the QYs decrease slightly. For the red colour (λem =660nm) QDs, the QYs can reach to as high as 28.2%, and for the other colour QDs they can also have the QYs above 22%. Time-resolved photobleaching experiments show that the fluorescent QDs-starch composite has a half-decay time of 40.23s. These results indicate that the CMS-Na is a promising QDs dispersant to obtain high QY QD composites.