Lithium Glass Scintillator Research Articles

Neutron transmission measurements for silica glass at the KURNS-LINAC

Silica glass has been used as a base and host material in vitrified radioactive waste and lithium glass scintillators for neutron detection because of its superb transparency, high heat resistance, and excellent chemical inertness. Therefore, an accurate total cross section of the silica glass is crucial to evaluate the criticality safety of vitrified wastes and understand the neutron response for lithium glass scintillators. This study performed neutron transmission measurements for silica glass using a pulsed neutron beam with the time-of-flight method at the Kyoto University Institute for Integrated Radiation and Nuclear Science − Linear Accelerator to provide an accurate total cross section in the thermal and epithermal energy range. We obtained the neutron total cross section of the silica glass in the energy region from 0.002–25 eV. The results were compared and discussed with previous results and evaluated data.

Field tests for performance evaluation of a new spent-fuel verification system in heavy water reactor

The optical fiber-based measurement system has been utilized for inspecting CANDU-type spent fuel at the Wolsung site in South Korea under the nuclear safeguards of the International Atomic Energy Agency (IAEA). In our previous studies, we developed a new spent-fuel verification system to address issues of the existing instrument. While our prior work primarily focused on equipment development, we had not yet conducted comprehensive field tests to assess its performance. Recently, we conducted field tests at the Wolsung Unit 4 to thoroughly evaluate the newly developed spent-fuel verification system's performance. This paper discusses the results of these field tests, with a focus on signal sensitivity, the system's capability to distinguish neighboring spent-fuel bundles, and the optical fiber background signals. Additionally, we conducted experiments to assess how different scintillation materials impact the system's performance, including p-terphenyl organic scintillator, PVT plastic scintillator, and lithium glass scintillator. The experimental results demonstrated that the new instrument equipped with the p-terphenyl organic scintillator outperformed the existing system. The p-terphenyl scintillator emerged as the superior choice among the three radiation scintillators. Signals that were previously undetectable using the Li glass scintillator were observed in the signals obtained with the p-terphenyl and PVT plastic scintillators. The remarkable performance of the new verification instrument is attributed mainly to the p-terphenyl's high light output and low decay time. The newly developed verification system is expected to streamline IAEA safeguards inspection efforts, reducing both time and the burden on nuclear operators. This report represents the first successful application of the p-terphenyl scintillator as a radiation detector in a wet spent fuel pool. The experimental findings presented in this paper are anticipated to be valuable for researchers working on radiation detectors suitable for high radiation environments in water.

Safeguards equipment for the spent nuclear fuel of pressurized heavy water reactors

This paper describes the implementation of newly developed safeguards equipment for the spent nuclear fuel of heavy water reactors stored in a wet interim storage facility. The developed equipment compensates for imperfections in the existing equipment including the optical fiber probe system (OFPS) and improves the performance and user convenience. Specifically, the lithium glass scintillator currently used in the current OFPS was changed to a plastic scintillator with efficient and cost-effective detectors, and the probe design for the radiation measurements was also changed to facilitate replacement of the scintillator. In addition, the manual cable loading method, which is an obstacle method for implementing safeguards, was designed to be automatically loaded onto a drum-shaped structure using a motor. All analog systems such as radiation signal processing systems and cable loading systems that used to run along all the equipment were digitally replaced so that all operations could be done with display panels. Through these efforts, the new equipment resulted in improved performance and enhanced user convenience. The replacement of the scintillators and probes improved the performance by about 10 times, and the new equipment design reduced the number and weight of the parts to less than half that of the existing equipment. The performance of the newly developed equipment was verified so that it can be used as new IAEA safety equipment, and it is expected to have a major role in implementing safeguards for spent nuclear fuel through its registration as IAEA inspection equipment.

Design and Optimisation of a Three Layers Thermal Neutron, Fast Neutron and Gamma-Ray Imaging System

The design and configuration of a multi-layered imaging system with the ability to detect thermal neutrons, fast neutrons and gamma rays has been developed and its efficacy demonstrated. The work presented here numerically determines the systems efficiency and spatial resolution, using 252Cf and 137Cs as a case study. The novelty of this detection system lies in the use of small form factor detectors in a three-layer design, which utilises neutron elastic scattering and Compton scattering simultaneously. The current configuration consists of 10 mm thick natural lithium glass (GS10) scintillator integrated with a 20 mm thick plastic scintillator (EJ-204) in the first layer, a 15 mm thick lithium glass (GS10) scintillator in the second and a 30 mm thick CsI(Tl) scintillator forming the final layer. Each of these layers is backed with an 8 x 8 silicon photomultiplier diode (SiPM) array. The overall size of the imaging system is 27 mm x 27 mm x 135 mm. MCNPv6.1 and Geant4-10.04 were alternatively used to optimise the overall configuration and to investigate detection modalities. Results show promising performance with high precision source localisation and characterization abilities. Measurements were virtually obtained of two gamma-ray sources within steel enclosures at angles of 15°, 30° and 50° separation in order to test spatial resolution ability of the system. With the current active size of the system and the 8x8 SiPM configuration, the results estimate the spatial resolution to be close to 30°. The ability of the system to characterise and identify sources based on the type and energy of the radiation emitted, has been investigated and results show that for all radiation types the system can identify the source energy within the energy range of typical reported sources in literature.

Evaluation of lithium glass scintillation detector responses for tritium production rate measurement in blanket neutronics experiments using the PHITS code

Lithium (Li) glass scintillation detectors were utilized by the neutron response of a 7Li glass subtracted from the neutron response of a 6Li glass to evaluate the tritium production rate (TPR) in the fusion blanket neutronics experiments, which is a so called Li glass method. TPRs in the Li2O blanket and the Li/V-alloy blanket were measured by a 6Li2O and a 6Li2CO3 pellet method, and by the Li glass method in the benchmark neutronics experiment with D-T neutrons at the Fusion Neutronics facility (FNS) of JAERI. TPRs measured by the Li glass method are lower than TPRs measured by the pellet method. The neutron responses of Li glass detectors have been calculated to study the discrepancies of two different methods by using the PHITS code. In the blanket, the neutron spectra change to harder from the backside to the front side of blanket. The reaction rate of several reactions, such as 6Li(n, n’α)D, 7Li(n, n’α)T, 7Li(n, 2n)6Li, and the elastic scattering of 6Li and 7Li increase with the neutron energy. The low-energy neutron peak was considered only for the calculation of TPR from Li glass, which loses the information of the 6Li(n, α)T reaction from high-energy neutron range. In addition, the reaction rate of this peak evaluated by the Li glass method is lower than real TPR of this peak for 6Li glass caused by weakened effect from other reactions. Therefore, the ratios of this peak reaction rate from the Li glass method against the total TPR of 6Li glass were evaluated to be a correction factor to correct Li glass method. After the correction, TPRs measured by Li glass method agree well with TPRs measured by pellet method.

Optimization of lithium-glass fibers with lithium depleted coating for neutron detection

Abstract Neutron-detecting scintillating glass uses 6 Li to capture thermal neutrons to produce an α and triton particles, which have ranges of 6 μ m and 36 μ m , respectively. Captures on or near the surface of the glass can cause one of the particles to deposit less than its full energy in the glass; resulting in a failure to detect the neutron. This effect can be mitigated in lithium glass scintillators by coating lithium-glass fibers with lithium depleted scintillating glass. Thus, the scintillator’s efficiency will be increased. Results from this work on glass scintillating fibers show that an increase up to 60% in neutron intrinsic efficiency depending on core size can be achieved with scintillating glass coatings .

Compact lithium-glass neutron beam monitor for SANS at CSNS

A small-angle scattering neutron spectrometer for material research is under construction at the China Spallation Neutron Source. An intervening neutron beam monitor behind the sample is needed to measure the beam intensity in order to reduce the measurement uncertainty caused by beam fluctuation. Considering the mobility requirement and limited space, we proposed a compact monitor using a type of lithium-glass scintillator provided by China Building Materials Academy. Its performance was studied experimentally using $$^{252}{\hbox {Cf}}$$ and $$^{60}{\hbox {Co}}$$ sources. The neutron light yield of the selected scintillator was measured to be $$5.3\times 10^3$$ photons/neutron. The feasibility of n-gamma discrimination using the charge comparison method was verified. By using the Geant4 toolkit, the monitor was modeled with precise physical processes including neutron tracking, scintillation, and optical photon transmission. The gamma sensitivity and detection efficiency were investigated in the simulation. It was concluded that a 0.5-mm-thick lithium-glass scintillator with natural lithium is an appropriate choice to satisfy both the neutron detection efficiency and gamma elimination requirements.

Simulation of Gamma-Ray and Neutron Spectrometers for Microsatellite Missions

Microsatellites have recently opened windows of frequent and low cost missions for planetary exploration. The performance of gamma-ray and neutron spectrometers on future microsatellite missions is simulated to assess the possibility of observation of hydrogen and major elements, given their concentration on the observation target. The measured elemental abundance will provide important geological constraints, and some of them may serve as space resources. Four different types of target bodies with various hydrogen concentrations in the range of 0 - 20,000 ppm are assumed as target compositions; Earth’s core, C-type, S-type and Martian meteorites. Gamma-ray and neutron emission rates show unique footprints that are related to the different elemental compositions. The starting point is the solid angle subtended between observation target and spectrometers that allow estimating the gamma-ray and neutron count rates emitted by the celestial bodies. In this work, three types of gamma-ray detectors; high-purity germanium (HPGe), CeBr3 and LaBr3(Ce), a neutron spectrometer combining a lithium glass scintillator with a boron loaded plastic scintillator and a dual mode spectrometer Cs2LiYCl6(Ce) (CLYC) are simulated, focusing on their observation backgrounds as a model case for microsatellite based measurements. The background count level of both gamma-ray (except for the LaBr3 detector) and neutron count rates was negligible under these particular conditions. The gamma-ray detectors were compared by the figure of merit, which was determined by their efficiency and energy resolution. It was found that each detector has unique advantages. The HPGe detector has the highest figure of merit due to its excellent energy resolution, whereas the CLYC detector is low in weight and power consumption due to its dual sensitivity to gamma-ray and neutron. The CeBr3 detector is an intermediate choice. The neutron count rates are calculated separately in three energy ranges, i.e. , thermal ( 500 keV), as a function of the hydrogen concentration in the 0 - 20,000 ppm range. The thermal and epithermal neutron count rates are found to decrease with hydrogen concentration, while the fast neutron count rate increases with the target average atomic mass. The optimal detector should be decided by the mission restraints on mass, power consumption, and heat thermal design.

Characteristics of the 2012 model lithium-6 time-analyzer neutron detector (LiTA12) system as a high efficiency detector for resonance absorption imaging

Neutron resonance absorption imaging, being used to visualize a spatial distribution of elements and/or temperature within a sample, is one of the important applications of an intense short-pulse neutron source. Two-dimensional time-analyzer neutron detectors are indispensable to perform neutron energy dependent imaging by means of the time-of-flight technique. Some state-of-the-art time-analyzer neutron detectors have been developed for thermal or cold neutrons. However the detection efficiencies of such neutron detectors are not sufficient for neutron resonance absorption imaging which utilizes neutrons in the energy region from eV to keV.The 2012 model lithium-6 time-analyzer neutron detector (LiTA12) system, based on a lithium glass scintillator and multi-anode photomultiplier tube, has the highest neutron efficiency among the detectors for pulsed neutron imaging together with the flexibility to tune the efficiency by changing the thickness of the lithium glass. The authors estimated performances of the detector at resonance neutron energies finding that 0.7 mm width line pairs made by 3 μm thick gold could be resolved at 4.9 eV and the maximum count rate of 8 Mcps was achieved at 1 keV.

The Breakup Cross Section of the D+D Reaction at 6.94 MeV

The D+D reactions are well known and widely used for a variety of purposes, mainly because of the use of the D(d , n )3 He reaction as a mono-energetic neutron source. The least studied of the D+D reactions is the D(d , n )pD reaction known as the deuteron breakup reaction, which produces a continuum of neutrons at energies below the monoenergetic peak. The neutron energy distribution as a function of angle for the cross section, , of the D(d ,n )pD reaction has been measured using a 6.94-MeV pulsed deuteron beam incident upon a D2 gas target. The time-of-flight technique was used to determine the energy of the neutrons detected in an array of two lithium glass scintillators and one NE-213 scintillator. The breakup cross section was determined as low as 225-keV neutron energy in the lithium glass detectors.

Influence of linear energy transfer on the scintillation decay behavior in a lithium glass scintillator

We analyzed the effects of linear energy transfer (LET) on the scintillation properties of a Li glass scintillator, GS20. The temporal profiles of scintillation were measured by using pulsed ion beams with different LETs. The rise in the temporal profiles of scintillation was faster for higher LET, whereas the decay part did not vary significantly for different LETs. The LET effects in the rise were ascribed to excited state interactions during the energy transfer process from the host glass to the luminescent centers, Ce3+ ions. If the light yield decreases with LET, the fast rise at high LET could be explained by the competition between energy transfer and quenching due to the excited state interactions.

Measurement of Fission Neutron Spectrum and Multiplicity using a Gamma Tag Double Time-of-flight Setup

Recent efforts have been made to improve the prompt fission neutron spectrum and nu-bar measurements for Uranium and Plutonium isotopes particularly in the keV region. A system has been designed at Rensselaer Polytechnic Institute (RPI) utilizing an array of EJ-301 liquid scintillators as well as lithium glass and plastic scintillators to experimentally determine these values. An array of BaF2 detectors was recently obtained from Oak Ridge National Laboratory to be used in conjunction with the neutron detectors. The system uses a novel gamma tagging method for fission which can offer an improvement over conventional fission chambers due to increased sample mass. A coincidence requirement on the gamma detectors from prompt fission gammas is used as the fission tag for the system as opposed to fission fragments in a conventional fission chamber. The system utilizes pulse digitization using Acqiris 8 bit digitizer boards which allow for gamma/neutron pulse height discrimination on the liquid scintillators during post processing. Additionally, a 252Cf fission chamber was designed and constructed at RPI which allowed for optimization and testing of the system without the need for an external neutron source. The characteristics of the gamma tagging method such as false detection rate and detection efficiency were determined using this fission chamber and verified using MCNP Polimi modeling. Prompt fission neutron spectrum data has been taken using the fission chamber focusing on the minimum detectable neutron energy for each of the various detectors. Plastic scintillators were found to offer a significant improvement over traditional liquid scintillators allowing energy measurements down to 50 keV. Background was also characterized for all detectors and will be discussed.

Reaction rates in blanket assemblies of a fusion-fission hybrid reactor

To validate neutronics calculation for the blanket design of fusion-fission hybrid reactor, experiments for measuring reaction rates inside two simulating assemblies are performed. Two benchmark assemblies were developed for the neutronics experiments. A D-T fusion neutron source is placed at the center of the setup. One of them consists of three layers of depleted uranium shells and two layers of polyethylene shells, and these shells are arranged alternatively. The U-238 capture reaction rates are measured using depleted uranium foils and an HPGe gamma spectrometer. The fission reaction rates are measured using a fission chamber coated with depleted uranium. The other assembly consists of depleted uranium and LiH shells. The tritium production rates are measured using the lithium glass scintillation detector which is placed in the LiH region of the assembly. The measured reaction rates are compared with the calculated ones predicted using MCNP code, and C/E values are obtained.

A position-sensitive detector with lithium glass and MaPMT

A position-sensitive detector is designed for neutron detection. It uses a single continuous screen of a self-made lithium glass scintillator, rather than discrete crystal implementations, coupling with a multi-anode PMT (MaPMT). The scintillator is fast and efficient; with a decay time of 34 ns and thermal neutron detection efficiency of around 95.8% for the 3 mm thick screen, and its light yield is around 5670 photons per neutron and 3768 photons per MeV γ rays deposition. The spatial resolution is around 1.6 mm (FWHM) with the energy resolution around 34.7% by using α (5.2 MeV) rays test.

Crystal Growth and Scintillation Properties of Ce<sup>3+</sup> and Mg<sup>2+</sup> Co-Doped LiCaAlF<sub>6</sub> Single Crystal

Ce and Mg Co-Doped LiCaAlF6 (LiCAF) Single Crystals Were Grown by Micro-Pulling-down (μ-PD) Method and the Optical and Scintillation Properties of Obtained Crystals Were Measured. The Grown Crystals Were Crack-Free and Had 30-50 mm in Length and 2 Mm in Diameter. Absorption Coefficients Were Proportional to the Ce Nominal Concentrations. the Radioluminescence Spectra under 5.5 Mev Alpha-Ray Irradiation Showed Emission Peak at 290 and 310 nm due to Ce3+ 5d-4f Transitions, and Were Agreement with those of Ce Single-Doped LiCaF. The Highest Light Yield under 5.5 Mev Alpha-Ray Irradiation of Ce 4% and Mg 2% Co-Doped LiCaF Was Found to Be 0.6 Times than that of Lithium Glass Scintillator GS-20. Comparing the Light Yield of Licaf Samples with the Fixed Ce Nominal Concentration and Different Mg Co-Doped Concentrations, the Light Yield Increased with an Increase of Mg Nominal Concentration. the Alpha-Ray Excited Decay Times Were Constantly 45-50 ns.

Neutron Spectrometer with Capture-Gated Liquid Scintillator

We have developed a capture-gated neutron spectrometer with a liquid scintillator and a lithium glass scintillator. The neutron-scattering signals from the liquid scintillator and the neutron-capture signals from the lithium glass scintillator were processed and collected separately by using a digital pulse processing technique. Neutron and gamma separation was performed using a pulse shape discrimination technique, which showed a 98 % selection capability above a neutron energy of 1 MeV. The correlation between the incident neutron energy and analogue-to-digital converter (ADC) values of the liquid scintillation counter was obtained by using a time-of-flight method to measure the neutrons emitted from a 252 Cf source. The correlation function of the ADC values and the neutron energy allowed us to determine the neutron energy by using only the ADC values of the liquid scintillation detector for capture-gated events. This work shows that the capture-gated neutron spectrometer can be used in neutron dosimetry.

Construction of monoenergetic neutron calibration fields using 45Sc(p, n)45Ti reaction at JAEA

The 8 and 27 keV monoenergetic neutron calibration fields have been developed by using (45)Sc(p, n)(45)Ti reaction. Protons from a 4-MV Pelletron accelerator are used to bombard a thin scandium target evaporated onto a platinum disc. The proton energies are finely adjusted to the resonance to generate the 8 and 27 keV neutrons by applying a high voltage to the target assemblies. The neutron energies were measured using the time-of-flight method with a lithium glass scintillation detector. The neutron fluences at a calibration point located at 50 cm from the target were evaluated using Bonner spheres. A long counter was placed at 2.2 m from the target and at 60 degrees to the direction of the proton beam in order to monitor the fluence at the calibration point. Fluence and dose equivalent rates at the calibration point are sufficient to calibrate many types of the neutron survey metres.

Low-energy neutron flux measurement using a resonance absorption filter surrounding a lithium glass scintillator

The resonance absorption filter technique has been used to determine the thermal/epithermal neutron flux. The main idea in this technique is to use an element with a high and essentially singular resonance in the neutron absorption cross section as a filter surrounding a miniature-type lithium glass scintillator. The count with and without the filter surrounding the detector gives the number of resonance-energy neutrons. Some preliminary results and a comparison with the MCNP code are shown.

BNCT neutron beam characterization using a resonance absorption filter method

The use of a resonance filter technique based on either a BF 3 or a miniature lithium–glass scintillator is described. The principles affecting the choice of suitable resonance absorber materials are discussed, and some preliminary results are shown.

Measurement and analysis of integral fusion neutronics data on simulated experimental lithium-lead module at the LOTUS facility

In-system foil activation rates and tritium production rates were measured in an experimental lithium-lead module (EL2M)- major component being a 62-cm thick pseudo-cylindrical region containing lithium and lead pellets so arranged as to simulate Li17Pb8.3 eutectic—at fusion blanket neutronics facility LOTUS. Sets of two foils each—Zr and In—were irradiated at multiple locations in the central rod to measure90Zr(n,2n)89m+gZr and115In(n,n′)115mIn reaction rates. Tritium measurements were done using two techniques: off-line liquid scintillation technique of Dierck and online lithium glass scintillation technique, the latter technique providing only T6 (tritium from6Li). These measurements have been analyzed both by two-dimensional and three-dimensional transport codes DORT and MCNP, respectively. Though computed results broadly reproduce spatial profiles (along the central rod) of the measured quantities, differences as large as 50% are found.