Search

The response of a gamma-ray spectrometer is generally determined by analyzing full-energy peaks. However, full-energy peaks cannot be measured easily in the case of scintillation detectors that consist of light elements, such as glass scintillators. Only a strong Compton plateau appears in the spectrum of such detectors. Therefore, Compton edgers were used to evaluate the response of these detectors. The response of a low-resolution 6 Li-glass detector to gamma rays was measured for the first time by a coincidence method with a high-resolution LaBr 3 :Ce detector using cascade gamma rays (2.75 and 1.37 MeV) from a 24Na source. Coincidence gates were applied at the peaks of the spectrum of the LaBr 3 :Ce detector at the 0.51 MeV annihilation peak, and the sum peaks of a gamma ray and a backscattered gamma ray. By analyzing the gated spectra of the 6 Li-glass detector, the energy-dependent detector response (i.e., the output strength and its dispersion) was determined. • Evaluation of the response characteristics, including signal output and broadening, of a low-resolution 6Li-glass detector to gamma rays up to approximately 2.5 MeV. • Coincidence measurement of cascade gamma rays emitted from a 24Na source with a high-resolution detector, a LaBr 3 :Ce detector. • Peak analysis of the spectra of the 6Li-glass detector gated at gamma ray peaks of the LaBr3:Ce detector. [ABSTRACT FROM AUTHOR]

This work aims at the investigation of the Pulse Shape Discrimination (PSD) capabilities of two very compact detection systems composed of a 3x3x3 cm3 EJ 276 and a 3x3x3 cm3 EJ 276G (the latter green shifted version) plastic scintillators, both coupled to Silicon Photomultiplier (SiPM). The studied systems are supposed to be the basic elementary cell of a new multi-detector for simultaneous detection of neutrons and light charged particles called NArCoS (Neutron Array for Correlation Studies) having both high angular and energy resolution. In this perspective, the results of the experimental qualification of two prototypes with gamma and alpha radioactive sources and in beam tests are reported, in order to characterize the optimum choice for the new device. [ABSTRACT FROM AUTHOR]

The radiation damage to a silicon photomultiplier (SiPM) set on a satellite orbit increases energy threshold for scintillator detectors. We confirmed that 1 krad of radiation increases the energy threshold by approximately a factor of 10, which is worst for our system. Using one or two SiPMs damaged by proton irradiation and a plastic scintillator, we performed the following three experiments in our attempt to lower the energy threshold of radiation-damaged SiPMs to the greatest extent: (1) measurements using a current waveform amplifier rather than a charge-sensitive amplifier, (2) coincidence measurements with two radiation-damaged SiPMs attached to one scintillator and summing up their signals, and (3) measurements at a low temperature. Our findings confirmed that the use of a current waveform amplifier, as opposed to a charge-sensitive amplifier and a shaping amplifier, could lower the energy threshold to approximately 65% (from 198 keV to 128 keV). Furthermore, if we set the coincidence width appropriately and sum up the signals of the two SiPMs in the coincidence measurement, the energy threshold could be lowered to approximately 70% (from 132 keV to 93 keV) with little loss of the acquired signal, compared to that of use of only one scintillator. Finally, if we perform our measurements at a temperature of −20 °C, we could lower the energy threshold to approximately 34% (from 128 keV to 43 keV) compared to that of at 20 °C. Accordingly, we conclude that the energy threshold can be lowered to approximately 15% by using a combination of these three methods. • Radiation damage increases the energy thresholds of SiPMs. • Using a current waveform amplifier can lower the energy threshold. • Coincidence measurement with two SiPMs and a scintillator can lower the energy threshold. • Measurement at low temperature can lower the energy threshold. [ABSTRACT FROM AUTHOR]

Aimed at beta spectrometry and dosimetry for mixed beta-gamma fields, a Si-plastic scintillator coincidence beta-ray spectrometer has been developed. The spectrometer collects pure beta-ray spectra by rejecting the gamma-ray detection events through coincidence. Both pulse height and arrival time of each detection event were recorded in list mode by a compact digital processing system. Spectral measurements were carried out using mixed beta-gamma fields from 90Sr/90Y and 137Cs sources for various beta and gamma count rates to evaluate the system performance. Coincidence beta spectra were collected for four fixed beta count rates (7.3–241 cps) from 90Sr/90Y while the gamma count rate from 137Cs was varied from 500 to 8000 cps. The coincidence beta spectrum was stable and unperturbed by the gamma detection events for most measurements while notable perturbation was observed in the low energy region when the beta to gamma count ratio is very low. • A beta spectrometer with a silicon detector and a plastic scintillator was developed. • The Coincidence algorithm was designed to reject gamma events. • Measured coincidence spectra were consistent in most count rates. • A distortion in spectrum was observed in the low energy region only at a very low beta to gamma count ratio. [ABSTRACT FROM AUTHOR]

This work presents a systematic study of the properties (Light Output Non-Uniformity (LONU) and energy resolution) of two CsI(Tl) scintillation units over a span of almost three years, under adverse conditions of humidity and temperature. These two crystals are part of the CALIFA detector, a highly segmented calorimeter and spectrometer for γ rays and light-charged particles, that is placed surrounding the reaction target at Cave C, the experimental cave of the R 3 B (Reactions with Radioactive Relativistic Beams) collaboration at the GSI-FAIR facilities in Darmstadt, Germany. The findings obtained after the experiment indicate that there was no significant impact on the performance in terms of resolution and LONU. This suggests that the employed wrapping for light collection effectively serves as an excellent barrier against humidity. As a result, the crystal is preserved in a far better condition than initially anticipated. [ABSTRACT FROM AUTHOR]

We report on a highly selective experimental setup for particle- γ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University (FSU) using fast CeBr 3 scintillators for γ -ray detection. Specifically, we report on the results of characterization tests for the first five CeBr 3 scintillation detectors of the CeBr 3 Array (CeBrA) with respect to energy resolution and timing characteristics. We also present results from the first particle- γ coincidence experiments successfully performed with the CeBrA demonstrator and the FSU SE-SPS. We show that with the new setup, γ -decay branching ratios and particle- γ angular correlations can be measured very selectively using narrow excitation energy gates, which are possible thanks to the excellent particle energy resolution of the SE-SPS. In addition, we highlight that nuclear level lifetimes in the nanoseconds regime can be determined by measuring the time difference between particle detection with the SE-SPS focal-plane scintillator and γ -ray detection with the fast CeBrA detectors. Selective excitation energy gates with the SE-SPS exclude any feeding contributions to these lifetimes. [ABSTRACT FROM AUTHOR]

A network of specialist laboratories support the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) with re-measurements of radionuclide samples, including xenon gas. The measurement of four xenon fission product radionuclides ( 133 Xe, 135 Xe, 131m Xe and 133m Xe) can be used to detect an underground nuclear explosion. Laboratories use a range of techniques to measure the radionuclides, including beta-gamma (β − γ) coincidence spectrometry. These highly-sensitive measurements are capable of detecting concentrations of down to 500 atoms of 133 Xe in a few cm 3 of xenon. In some detector systems, detection of the metastable isomers ( 131m Xe and 133m Xe) can be more challenging due to interferences between the signatures of different radionuclides. Recent work has shown that using high-purity Germanium (HPGe) high-resolution gamma detectors, these interferences can be reduced, lowering the dependence of the detection limits on radionuclide sample isotopic composition. One downside of these detectors is the reduction in detection efficiency, which impacts the overall detection sensitivity; so assessing different detector systems is a priority for radionuclide laboratories. This work presents a coincidence detector system comprising of a plastic scintillator gas cell and a large-crystal high-purity germanium detector. The energy resolution, coincidence detection efficiency, MDA and interference factors are determined from measurements of synthetic radioxenon gas samples. • A plastic scintillator and HPGe β − γ coincidence system has been configured for the measurement of isotopes of radioxenon • Calculations show that this type of setup can improve the detection limits compared to other systems. • High-resolution γ -detectors can separate Xe and Cs X-rays, decreasing interference. [ABSTRACT FROM AUTHOR]

Neutron spectrometry is important for radiation metrology, radiation protection, accelerator physics etc. The spectral response of a capture-gated detector to mono-energetic neutrons contains a significant peak, making it easy to be analyzed. But this system output not only capture-gated events (CGE) but also chance coincidence events (CCE). It is critical to identify and eliminate CCE. However, chance coincidence has not been analyzed in detail before. This paper aims to find a way to eliminate CCE and get the spectrum of CGE. Thus, categories of CCE were analyzed and their probability equations were established. Then recorded pulses from a composite scintillator measured in mixed radiation fields were used to verify CCE and explore the influence of timing gate. Results show that n/γ discrimination is effective to distinguish CCE caused by γ-rays and calculate the amount of CCE caused by fast neutrons. Timing gate should be determined according to the different distributions of CGE and CCE. Spectrum of CGE can be acquired by subtracting that of fast neutron CCE from the fast neutron spectrum of coincidence events. • Categories and probabilities of chance coincidence events (CCE) are analyzed for capture-gated neutron spectrometry. • Time distributions of capture-gated events (CGE) and CCE are calculated to determine timing gate. • The amount of fast neutron CCE is computed with that of γ-ray CCE identified via n/γ discrimination. • Spectrum of coincidence events is decomposed into spectra of CGE and fast neutron CCE. [ABSTRACT FROM AUTHOR]

Measurement of the four relevant radioxenon isotopes, namely 131m Xe, 133m Xe, 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 131m Xe, 133m Xe, 133Xe and 135Xe can achieve 1.8 mBq, 1.4 mBq, 3.4 mBq and 4.1 mBq, respectively. [ABSTRACT FROM AUTHOR]

Recent theoretical and experimental results have brought renewed interest and focus on the topic of fission fragment angular momentum. Measurements of neutrons and γ rays in coincidence with fission fragments remain the most valuable tool in the exploration of fission physics. To achieve these scientific goals, we have developed a system that combines a state-of-the-art fission fragment detector and n − γ radiation detectors. A new twin Frisch-gridded ionization chamber has been designed and constructed for use with a spontaneous fission source and an array of forty trans -stilbene organic scintillators (FS-3) at Argonne National Laboratory. The new ionization chamber design we present in this work aims at minimizing particle attenuation in the chamber walls, and provides a compact apparatus that can be fit inside existing experimental systems. The ionization chamber is capable of measuring fission fragment masses and kinetic energies, whereas the FS-3 provides neutron and γ -ray multiplicities and spectra. The details of both detector assemblies are presented along with the first experimental results of this setup. Planned event-by-event analysis and future experiments are briefly discussed. [ABSTRACT FROM AUTHOR]

The goal of the present work is to develop a time-of-flight positron emission tomography (TOF-PET) detector system with 100 picosecond (ps) coincidence time resolution (CTR) using arrays of 20 mm length scintillator crystal elements. If successful, this would yield a 1.5-fold better reconstructed image signal to noise ratio (SNR) compared to state-of-the-art clinical TOF-PET systems. The proposed detector configuration comprises LGSO scintillation crystal elements optically coupled to silicon photomultipliers (SiPMs) which are read out by a fast, high precision, multi-channel amplifier/comparator integrated circuit (IC). Results obtained with that IC were compared with those achieved using a high-frequency (HF) readout, comprising discrete element readout for each detector channel. CTR values of 89.6 ± 0.8 ps and 105.1 ± 0.9 ps FWHM were achieved with the HF readout for 3 × 3 × 3 mm3 and 3 × 3 × 10 mm3 LGSO crystals, respectively, and 92.8 ± 0.9 ps and 114.1 ± 1.1 ps FWHM were achieved using the IC board for the same crystal elements. These results demonstrate the capabilities of a scalable IC readout solution for a 100 ps CTR TOF-PET design. [ABSTRACT FROM AUTHOR]

We describe a technique, applicable to liquid-argon-based dark matter detectors, allowing for discrimination of alpha-decays in detector regions with incomplete light collection from nuclear-recoil-like events. Nuclear recoils and alpha events preferentially excite the liquid argon (LAr) singlet state, which has a decay time of ∼ 6 ns. The wavelength-shifter TPB, which is typically applied to the inside of the active detector volume to make the LAr scintillation photons visible, has a short re-emission time that preserves the LAr scintillation timing. We describe the production method and characterization of a wavelength-shifting polymeric film – pyrene-doped polystyrene – which we developed for the DEAP-3600 detector. At liquid argon temperature, the film's re-emission timing is dominated by a modified exponential decay with a time constant of 279(14) ns, and has a wavelength-shifting efficiency of 46.4(2.9)% relative to TPB, measured at room temperature. By coating the detector neck (a region outside the active volume where the scintillation light collection efficiency is low) with this film, the visible energy and the scintillation pulse shape of alpha events in the neck region are modified, and we predict that through pulse shape discrimination, the coating will afford a suppression factor of O (1 0 5 ) against these events. [Display omitted] • Wavelength shifter characterization. • Background rejection techniques for liquid argon detectors. • Cryogenic detector technologies. [ABSTRACT FROM AUTHOR]

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% Ce 3 + 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. [ABSTRACT FROM AUTHOR]

Organic glass scintillator (OGS) bars (6 × 6 × 50 mm 3) were melt-cast and characterized with dual-ended readout by silicon photomultiplier arrays. The results were compared to trans -stilbene bars of the same size. Energy resolution was measured via a 137Cs Compton-coincidence experiment. Time resolution was determined via a 22Na coincidence-timing experiment. Depth-of-interaction resolution was measured by moving a gamma-ray fan beam along the major axis of the bars. Pulse shape discrimination capability and neutron light output were determined via a time-of-flight measurement of a 252Cf source. The OGS bars exhibited better energy resolution at 478 keV (10. 3 ± 0. 5 % vs. 11. 2 ± 0. 5 %), better time resolution from 200–341 keVee (270 ps vs. 340 ps FWHM), slightly poorer depth-of-interaction resolution, poorer PSD performance, and higher neutron light output than the stilbene bars. The low cost, ease of manufacturing, brightness, and excellent time resolution make OGS a strong candidate for use in compact radiation imaging systems. [ABSTRACT FROM AUTHOR]

This paper describes an experimental setup developed to measure the beta-ray energy spectrum as well as a Geant4 simulation study conducted to characterize the properties of a beta-spectrometer. The beta-spectrometer comprises a multi-wire chamber to generate signals to indicate the incidence of beta rays and a plastic scintillation detector to measure its energy. The coincidence method of the detector signals was used to remove high gamma-ray interference. To evaluate the performance of the developed spectrometer, the energy spectra were measured with the radionuclide sources (137Cs and 207Bi) emitting internal conversion electrons and gamma rays. The gamma-ray interference removal rate of the spectrometer using the coincidence method was 99.12 ± 0.09%. To reconstruct the beta spectrum from the measured spectrum, Monte Carlo simulations using the Geant4 toolkit were performed to calculate the coefficient related to the effect of gamma rays. The obtained spectrum confirmed that the energy resolution and intrinsic internal conversion peak detection efficiency of the beta-spectrometer were 10.2% at 1 MeV and 91.6%, respectively. [ABSTRACT FROM AUTHOR]

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 E n 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 E n score as specified in the ISO13528:2015. The results of measurements are acceptable if E n ≦ 1.0. An E n 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. • Standardisation of 133Ba. • Efficiency extrapolation technique in variant of e, X -γ coincidence. • Plastic scintillator (PS) is used as beta detector. • Performance demonstration of PS based 4πβ-γ coincidence system for e, X -γ emitters. • Performance of PS system was evaluated with E n score. [ABSTRACT FROM AUTHOR]