Coincidence System Research Articles

The SNEWS 2.0 alert software for the coincident detection of neutrinos from core-collapse supernovae

The neutrino signal from the next galactic core-collapse supernova will provide an invaluable early warning of the explosion. By combining the burst trigger from several neutrino detectors, the location of the explosion can be triangulated minutes to hours before the optical emission becomes visible, while also reducing the rate of false-positive triggers. To enable multi-messenger follow-up of nearby supernovae, the SuperNova Early Warning System 2.0 (SNEWS 2.0) will produce a combined alert using a global network of neutrino detectors. This paper describes the trigger publishing and alert formation framework of the SNEWS 2.0 network. The framework is built on the HOPSKOTCH publish-subscribe system to easily incorporate new detectors into the network, and it implements a coincidence system to form alerts and estimate a false-positive rate for the combined triggers. The paper outlines the structure of the SNEWS 2.0 software and the initial testing of coincident signals.

Development of a charged particle-[formula omitted] coincidence system for nuclear structure and reaction studies at TIFR

A new detector system for measurements of charged particles and γ-rays in coincidence has been developed at TIFR Mumbai, by coupling an annular double-sided segmented Si detector with an array of Compton-suppressed clover HPGe detectors. Digital data acquisition system has been configured for the setup, which has been calibrated and tested using the 229Th radioactive source that emits α-particles along with γ-rays. The functionality and performance of the coincidence apparatus for Doppler correction of γ-transitions emitted during the in-flight de-excitation of the projectile and the target in the 30Si + 197Au Coulomb excitation experiment have been demonstrated.

Digital coincidence counting with 4πβ(PPC)-γ for the standardization of 60Co

A 4πβ(PPC)-γ coincidence system has been made at KRISS based on a digital DAQ. 60Co sources were measured to verify the system. The maximum detection efficiency for beta particles was estimated to be 96.7 %. Massic activities for sample sources had 0.005 % of the sample variability error, which was well within the expanded standard uncertainty of 0.54 % (k = 2).

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.

Primary standardization and Monte Carlo modeling of (243Am + 239Np) by means of a 4π(PC)-γ coincidence counting system

The procedure followed by the Nuclear Metrology Laboratory (LMN) at the IPEN for the primary standardization of a (243Am + 239Np) solution, in secular equilibrium, is described. The measurement was carried out in a 4π(PC) (α,β)−γ coincidence system. The total activity per unit mass of the solution was determined by the extrapolation technique, using a software coincidence counting systsem. The extrapolation curves were compared with Monte Carlo calculations by means of Code ESQUEMA, used in previous works, which, was improved and applied in order to calculate the alpha, beta, gamma, X-rays and coincidence spectra.

Characterization of a [formula omitted]-[formula omitted] coincidence system comprising a plastic scintillator and HPGe detector for radioxenon measurements under the CTBT

Measurement of the four relevant radioxenon isotopes, namely 131mXe, 133mXe, 133Xe, and 135Xe, play a key role in underground nuclear explosion monitoring for ensuring compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). A β-γ coincidence system that employs a plastic scintillator detector and a HPGe detector was developed in Beijing Radionuclide Laboratory. The Minimum Detectable Activity (MDA) in a 24-h measurement of the system for 131mXe, 133mXe, 133Xe and 135Xe can achieve 1.8 mBq, 1.4 mBq, 3.4 mBq and 4.1 mBq, respectively.

A SiPM-based dual and triple coincidence system for positron annihilation lifetime measurement

Positron annihilation lifetime (PAL) spectroscopy is a powerful non-destructive method to study defects in materials. Silicon photomultipliers (SiPMs) have emerged as promising photodetector alternatives for PAL systems. However, further research is needed to fully optimize SiPM arrays for PAL applications. In this study, a dual and triple coincidence system has been developed based on four 1 × 4 SiPM arrays with resistor-chain readout, and initial results of PAL measurement have been obtained. A pixel-by-pixel time shift correction method was proposed and successfully applied using triple γ coincidence for summing 128 PAL spectra in one measurement. The system provides position, timing, and energy information for both 1275 and 511 keV γ-rays. The use of SiPM arrays and the pixel-by-pixel time shift correction method have enabled precise and reliable measurements of PALs in single-crystal silicon and yttria-stabilized zirconia samples. The developed SiPM-array-based PAL system also offers a technical solution to measure angular correlations of positron annihilation radiation, with the potential for further improvements.

Development and performance evaluation of a novel [formula omitted]-[formula omitted] coincidence analysis software

Processing of large amounts of data from a γ-γ coincidence system is a practical challenge in trace-level radionuclide measurements. Given the benefits and growing number of multidimensional gamma spectrometers worldwide, this is a major restriction in wide-spread applicability of coincidence techniques. This study demonstrates a novel γ-γ coincidence analysis software developed at Pacific Northwest National Laboratory, USA. The software utilizes advanced search techniques and Python libraries to readily identify coincidence signatures in the large data. Using both synthetic and experimental data, the study uncovers various strategies/libraries employed during software’s development. This work aims to provide a reference document in handling large data routinely encountered in trace-level measurements.

Novel Compton suppression equipment in [formula omitted]-ray spectrometry with list mode data acquisition

A novel Compton suppression device has been developed at the Radiation and Nuclear Safety Authority of Finland to improve the sensitivity of measurements in the Gamma Laboratory. It utilizes γ–γ anticoincidence, but operates as a full coincidence system. Specific software has been developed for the sorting, visualization and analysis of list mode data produced by the multi-detector list-mode devices in the Gamma Laboratory. By utilizing the software, the coincidence data can be accessed and the true-coincidence losses of photo-peaks of multiple gamma-ray-emitting nuclides restored in the analysis. This simplifies data analysis and further increases the sensitivity of the device in low count-rate gamma spectrometry.A detailed Geant4 simulation model of the device was developed and used to optimize the device as well as to support calibrations and complex analysis tasks.The setup has been integrated to current laboratory information management system used in the Gamma Laboratory. Compton suppression reduces the continuous background seen by the high-purity germanium detector by a factor of 3–10, in addition to comparable reduction in the Compton continuum of any peaks in the spectrum. A comparison with the results of conventional gamma-ray spectrometry is presented.

ELECTRON IRRADIATED EFFECT IN POLYURETHANES STUDIED BY POSITRON ANNIHILATION LIFETIME SPECTROSCOPY

The intensity variation of positronium as a result of electron irradiation has been studied on polyurethanes (PU) using positron annihilation lifetime spectroscopy (PALS). The PALS measurement was carried out at room temperature with a conventional fast-fast coincidence system. The lifetime spectra were analyzed into four components using melt program to extract the positron parameters such as lifetime and intensity. Due to irradiation a decrease of intensity about 2.7% was observed up to 10kGy. Free volume radius has been calculated for electron irradiated PU. PALS measurement has also been performed to study the effect of temperature variation in the range 30K to 310K. Analysis by melt program on the spectra shows that the fourth lifetime component increases significantly above glass transition temperature.

Dynamic imaging comparison of 18F-FDG tracers with Compton imaging and PET coincidence imaging

In the clinical situation of positron emission tomography (PET) scans, an activity of an approximately few hundred megabecquerels (3.7 MBq/kg) is used for injection. Monitoring and imaging of moving radioisotopes is useful in clinical applications, such as tracer injection and leakage monitoring in PET scan protocols. We have developed a Compton imaging and PET coincidence system to monitor a moving radioisotope using 8 × 8 GAGG crystal arrays coupled to SiPM arrays with dynamic time-over-threshold-based individual readout circuits, and its imaging performance is considered. The measured resolution of PET and Compton imaging is 3.2 mm and approximately 17 degrees for a 22Na point source. In the experiment, radiotracers with activities from 11.2 MBq to 93.3 MBq moving with speeds from 1 mm/s to 10 mm/s were used for mimicking the blood flow. Both reconstructed images of PET and Compton imaging successfully visualized the movement, except for Compton imaging in the 93.3 MBq case. PET shows better activity-tracking capability and radio-tracer speeds up to 100 MBq. In contrast, Compton imaging has a wider field of view (FOV) to monitor a larger area than the limited FOV in a PET system. We believe that this work can contribute to solutions of various medical problems such as blood flow measurement and extravasation detection.

Development of a miniature digital data processing 4πβ(LS)-γ(LaBr3) coincidence system at KRISS

A miniature 4πβ(LS)–γ(LaBr3) coincidence system for the activity measurement of beta-gamma-emitting nuclei was developed using digital data processing at the Korea Research Institute of Standards and Science (KRISS). The system was configured with two photomultiplier tubes for beta measurements, and two LaBr3 gamma detectors. A pilot experiment was conducted using a60Co source. The highest beta-detection efficiency achieved with 60Co was found to be 93.7%. The activity concentration with the new system was found to be (5665 ± 27) kBq (k = 2). This value is in agreement with the reference ionization chamber at KRISS within the uncertainty of the new system.

Design and Application of a β-γ Coincidence Measurement System Based on Digital Technology

In order to reduce the uncertainty of coincidence measurement, a β-γ coincidence measurement system based on digital technology is designed. The system consists of data acquisition hardware and data analysis software. It uses the data acquisition card to collect data from the detector, and then finish the dead time correction, coincidence resolving time correction and efficiency extrapolation necessary for coincidence measurement on the computer. The designed coincidence measurement system is used to measure 60Co standard source in the laboratory, and adopt two efficiency extrapolation methods to process the measurement results. The results show that the deviation of the activity of 60Co standard source measured using the designed coincidence system from the value measured using a standard device is less than 0.5%.

Time characterization of cosmic-ray induced events in HPGe detector by Monte Carlo simulations

Detailed studies of background events provide information necessary for the planning of active and passive shielding of the detector in all experiments, especially ones searching for rare nuclear events. An effective approach in understanding the contribution of cosmic rays to the background of the HPGe detector is the use of Monte Carlo simulations. In this study, the Monte Carlo simulations were performed in order to obtain the time spectrum of the events induced by cosmic-ray muons and neutrons in the materials in the vicinity of the detector system and the detector itself. In order to reject background events originating from environmental radionuclides (from 238U and 232Th series, 40K, etc.), a coincidence system based on a large-volume HPGe detector and plastic scintillation detector was developed and the same setup was constructed in simulations. The experimental spectrum was compared with the simulated one. The possibility to distinguish these events based on the time was presented and illustrated through the selection of several time intervals of the time spectrum obtained in the simulation and corresponding spectra.Furthermore, the contribution of the muon-induced neutrons and cosmic-ray neutron-induced events to the background spectrum of the large-volume HPGe detector was analyzed. It was found that neutrons produced in the interaction of cosmic-muons with detector shielding and the detector itself are relatively small contributors to the overall neutron-induced events (i.e. low-energy region up to 100 keV originating dominantly from recoils and gamma lines originating from inelastic neutron scattering) registered in coincidence spectrum of HPGe detector compared to the contribution of cosmic-neutron themselves. The share of neutron components in this low-energy region of the coincidence spectrum of the HPGe detector was estimated to be ≈88%. In experiments searching for hypothetical dark matter particles, expected signals are in this energy region, thus in this type of experiment, it is essential to perform rejection of events induced by neutron interaction, in order to avoid misidentification of registered signals.

Next-generation particulate monitoring

Operated by the Comprehensive Nuclear-Test-Ban Treaty Organisation, the International Monitoring System is used by almost 200 nations to monitor for nuclear weapons tests. The IMS is still under development, and the Comprehensive Nuclear-Test-Ban Treaty has not yet entered into force, however the radionuclide component has proved instrumental in radically changing both nuclear verification science and researchers’ understanding of the dynamic global radiation background. After more than 20 years, the network is mostly complete, however the technology utilised for the particulate monitoring component remains practically the same, despite a number of laboratories developing coincidence systems that can offer orders of magnitude improvements in detection sensitivity and reliability. This paper describes the status of the technology, and the advantages of implementing this within the International Monitoring System. Furthermore, the performance of a prototype system developed by the Comprehensive Nuclear-Test-Ban Treaty Organisation is presented, and the implications of introducing this technology considered.

Standardization of 129I using the movable 4πβ(LS)-X(NaI(Tl)) system

The 129I standardization, using the movable 4πβ(LS)−X(NaI(Tl)) coincidence system, was performed for two 129I radioactive sources – one was dissolved in 0.1M NaOH solution and the other in 0.1M HNO3 solution. The system incorporates three movable PM tubes for a β–counter placed on a plane and a X-ray detector that can be moved up to the bottom of the vial.The β-efficiency depending on the amount of radioactive solution was investigated with 14 liquid scintillation samples prepared by gravimetrically dispensing 4.4–145 mg of 129I radioactive solution. The β-efficiencies above 90% were observed at less than 56 mg, but it was at most 70% at 145 mg. This occurred regardless of the activity of the sample or the type of chemical solution used to dissolve 129I source. The activity concentration of each 129I source was determined by efficiency-extrapolation method for samples with an activity range of 0.28–4.5 kBq. The β-efficiency points were derived over 10 intervals by moving 3-PM tubes in fine steps of about 1 mm from the sample. The highest value for β-efficiency was 95%. The combined uncertainty were 0.25% and 0.26%, respectively. The stated precision obtained using the system is better than that previously reported in the literature obtained by the triple to double coincidence ratio (TDCR) or the CIEMAT/NIST efficiency tracing method.

Preliminary measurements using a Triple to Double Coincidence Ratio (TDCR) Liquid Scintillator Counter System

The preliminary measurements using a Triple to Double Coincidence Ratio (TDCR) Liquid Scintillator Counter System developed by the Nuclear Metrology Laboratory (LMN) at IPEN, is presented. The TDCR system makes use of three photomultipliers positioned at 120° relative angle, operating in coincidence. For this preliminarymeasurement, 14C was selected to be standardized; 14C was chosen due to be a pure beta emitter with low end-point energy of 156 keV, which is suitable to be measured by the TDCR system. This solution was previously calibrated by the efficiency tracing technique using a 4p(PC)b-g coincidence system, employing 60Co as a tracer. The activity of the 14C solution by efficiency tracing technique was determined by using the extrapolation technique, changing the beta efficiency by pulse height discrimination. In order to determine the final activity, a Monte Carlo simulation was used to generate the extrapolation curve. The Software Coincidence System (SCS) developed by the LMN was used for both systems to register the events. MICELLE 2 code was used to calculate the theoretical TDCR efficiency. Measurements using HIDEX, a commercial liquid scintillator system, were also carried out and the results from the three methods were compared, showing a good agreement.

Standardisation of 133Ba by efficiency extrapolation method and calibration of ionisation chamber

133Ba has been standardised by direct measurements for the first time in the laboratory using two counting systems: (i) the 4πβ (plastic scintillator) -γ coincidence, (ii) the 4πβ (proportional counter) -γ coincidence. Furthermore, this standardisation experiment demonstrates the performance and applicability of the recently developed 4πβ (plastic scintillator)-γ coincidence system for radionuclides decaying with complex decay schemes as well as for e, X-γ emitters. Additionally, 133Ba solution standards were prepared to calibrate the pressurized 4π γ ionisation chamber and determination of the calibration coefficient. The En score is a statistical indicator of the agreement between two independent estimations. Thus, the performance of the PS system was compared to the result obtained with the PC system using the En score as specified in the ISO13528:2015. The results of measurements are acceptable if En ≦ 1.0. An En score of 0.2 was obtained which indicates that, the 133Ba activity concentration obtained by the 4πβ (plastic scintillator) -γ coincidence and 4πβ (proportional counter) -γ coincidence systems are in agreement. This paper presents the standardisation procedure, the results obtained by the measurements and their comparison.

Development of a movable 4πβ(LS)−γ coincidence counting system for activity standardization of β−γ emitters

A new movable 3PM-γ coincidence system, based on 4πβ(LS)−γ coincidence counting, for activity measurement of β-γ emitters has been designed at the Korea Research Institute of Standards and Science (KRISS). The system incorporates 3 PM tubes on the plane and two detectors placed above and below the center of the plane. The 3 PM tubes for β–counters in the plane are movable up to 100 mm from a liquid scintillation vial, thus enabling the variation of β−detection efficiencies by a geometrical technique. A NaI(Tl) γ-counter was set above for the present work. The β-event is determined by counting the logical sum of three double coincidences. All the necessary electronics, i.e., logical sum, adjusting the duration of dead-time of each counting channel and coincidence resolving times, and analyzing coincidence relation, were specially designed to be fabricated in an integrated circuit. Details of the detectors, the electronics, the overall movable 3PM-γ coincidence system are presented, as well as the results of investigations to assess its operating characteristics. Validation measurements have been performed with 60Co and 57Co sources. The highest β−detection efficiency achieved with 60Co and 57Co was 97% and 95%, respectively. The activity concentration determined with a new system agreed with calibrated values within the uncertainty range. Further results from validation measurements and the corresponding uncertainty budgets are presented.

Gamma Spectrum Measurement Following the Nuclear Decay

In the present work, the detection systems and the data acquisition methods used in the nuclear decay study in our laboratory at Shanghai Institute of Applied Physics, CAS are introduced. These two detection systems include the low-background anti-Compton spectrometer and the three-parameter (γ-γ-t) coincidence system of HPGe-HPGe detectors, both of which are used to measure the γ rays following the nuclear β- and β++EC decays. In addition, as an example, the detection of γ rays following the β++EC decay of 74As, by using these two spectrometers, is described in detail.