Gamma-ray Scintillation Research Articles

Improvement of mechanical properties and radiation shielding performance of AlBiBO3 glasses using yttria: An experimental investigation

Nuclear radiation shielding and rigidity parameters of the newly developed Al(0.1-x)B0.6Bi1.8O3Y2x glasses were studied to elucidate their potential as gamma radiation shielding material. In this study, bismuth borate glass systems with different amount of yttria additive were synthesized using melt-quenching technique. The material properties such as radiation shielding performance, structural and mechanical behaviors have changed with yttria additive into Bi-borate glasses. To obtain these changes, x-ray diffraction, scintillation gamma-ray spectrometer, and pulse-echo measurements have performed. The results showed that yttria additive has increased the density of glasses as well as radiation shielding performance. Also, the rigidity parameters were investigated not only experimentally but also theoretically. The results showed that G5 sample is superior nuclear radiation shielding sample with lowest HVL and MFP values. Moreover, yttria additive has increased the bridging oxygen atoms, enhances the coordination number as well as the cross-link density. The enhancement of all of these parameters indicates that these glasses are an excellent candidate to be used as a radiation shielding material. It can be concluded that yttria additive for aforementioned glass system has an important impact in mechanical and nuclear shielding properties yet further investigations should be considered for different types of applications.

Data fusion methods for improving resolution from a gamma-ray scintillator network

Abstract Enhancements in gamma-ray spectral resolution have been realized through hardware development, including low-defect scintillation materials, solid-state detector technology, and low-noise read-out electronics. Enhanced resolution has also been provided by deconvoluting hardware response through the application of spectral unfolding techniques. However, fusing data from multiple independent measurements, both before and after spectral unfolding, to obtain more information than exists from a single measurement represents a largely unexplored path. This work provides a statistical foundation from which data acquired from an arbitrary number of independent gamma-ray spectra can be fused to yield higher resolution than the constituent measurements yield in isolation. Specifically, three data fusion techniques are considered: (i) pulse-height spectrum fusion, (ii) unfolded fluence linear opinion pool, and (iii) unfolded fluence logarithmic opinion pool. We explore the qualitative characteristics of these methods. We then apply them to spectra of thallium-doped sodium iodide [NaI(Tl)] and bismuth germanate (BGO), where all spectra are provided by MCNP simulations. Our results demonstrate improved resolution, thus establishing the methods as an inexpensive alternative to hardware upgrades. Moreover, our results demonstrate that these results have the potential to expand the capability of cutting-edge technology to provide currently unachievable resolution.

Study of runaway electrons in TUMAN-3M tokamak plasmas

Studies of runaway electrons in present day tokamaks are essential to improve theoretical models and to support possible avoidance or suppression mechanisms in future large-scale plasma devices. Some of the phenomena associated with the runaway electrons take place at faster time scales, and thus it is essential to probe the runaway electrons to investigate underlying physics. The present article reports a few experimental observations of runaway electron associated events, at fast time scales, using a state-of-the-art multi-detector system developed at the Ioffe Institute and recently deployed on the TUMAN-3M tokamak. The system is based on the high-performance scintillation gamma-ray spectrometers for measurements of bremsstrahlung generated during the interaction of accelerated electrons with plasma and materials of the tokamak chamber. It includes a total three detectors configured in the spectroscopic mode having different lines of sight. Along with this hardware, dedicated algorithms were developed and validated that enables the separation of piled-up pulses, maximize the dynamic range of the detector and provides a counting rate as high as 107 counts per second. The inversion code, DeGaSum, has been used for the reconstruction of a runaway electron energy distribution function from the measured gamma-ray spectra. Using this tool, experimental analysis of the runaway electron beam generation and evolution of their energy distribution in the TUMAN-3M representative plasma discharges is performed. The effect on gamma-ray count rate during the magnetohydrodynamic activities and possible changes in the runaway electron energy distribution function during sawtooth oscillations is discussed in detail. Possible maximum limit of the runaway electron energy in TUMAN-3M is investigated and compared with the numerical analysis. In addition, the probability of the runaway electron generation throughout the plasma discharge is estimated analytically and compared with the experimental observation that suggests a balance between production and loss of the runaway electrons.

Determination of effective atomic number of composite materials using backscattered gamma photons – A novel method

The effective atomic number (Zeff) of composite materials has been determined by measuring the backscattered gamma photons at 180°. A 661.6 keV gamma photons from 137Cs radioactive source are allowed to scatter at an angle of 180° from the sample. The backscattered photons at 180° from the sample are detected with “2 × 2″ NaI(Tl) scintillation gamma ray spectrometer coupled to 16 K Multi Channel Analyzer (MCA). It is observed experimentally that the intensity of backscattered photons increases initially with increasing the thickness of the target and then it becomes saturated above a certain thickness. By knowing the saturated thickness values for known atomic number of the elemental targets, the Zeff of composite materials has been determined. The experimentally measured Zeff values have been compared with theoretical values predicted by direct method, power law method and AutoZeff code.

Spectral windows analysis method for monitoring anthropogenic radionuclides in real-time environmental gamma-ray scintillation spectrometry

This paper proposes an analysis methodology based on the spectral windows technique aimed for environmental real-time gamma-ray spectra obtained with scintillation detectors. The method permits us to monitor activity concentrations of selected isotopes, such as anthropogenic radionuclides like 137Cs and 131I, by removing the Compton scattering plus other external contributions and resolving peak overlapping within any window. Activity concentrations are presented for 137Cs, 131I, 214Bi, and 214Pb when applying the method to a monitor using a LaBr3(Ce) detector. The method avoids false-positive and false-negative results of anthropogenic radionuclides in the presence of radiation from natural origins by obtaining activity concentrations that correspond to those obtained by a Gaussian fitting commercial software.

Mapping of radiation anomalies using UAV mini-airborne gamma-ray spectrometry

Localization of size-limited gamma-ray anomalies plays a fundamental role in uranium prospecting and environmental studies. Possibilities of a newly developed mini-airborne gamma-ray spectrometric equipment were tested on a uranium anomaly near the village of Třebsko, Czech Republic. The measurement equipment was based on a scintillation gamma-ray spectrometer specially developed for unmanned aerial vehicles (UAV) mounted on powerful hexacopter. The gamma-ray spectrometer has two 103 cm3 BGO scintillation detectors of relatively high sensitivity. The tested anomaly, which is 80 m by 40 m in size, was investigated by ground gamma-ray spectrometric measurement in a detail rectangular measurement grid. Average uranium concentration is 25 mg/kg eU attaining 700 mg/kg eU locally. The mini-airborne measurement across the anomaly was carried out on three 100 m long parallel profiles at eight flight altitudes from 5 to 40 m above the ground. The resulting 1 s 1024 channel gamma-ray spectra, recorded in counts per second (cps), were processed to concentration units of K, U and Th, while total count (TC) was reported in cps. Increased gamma ray intensity of the anomaly was indicated by mini-airborne measurement at all profiles and altitudes, including the highest altitude of 40 m, at which the recorded intensity is close to the natural radiation background. The reported instrument is able to record data with comparable quality as standard airborne survey, due to relative sensitive detector, lower flight altitude and relatively low flight speed of 1 m/s. The presented experiment brings new experience with using unmanned semi-autonomous aerial vehicles and the latest mini-airborne radiometric instrument. The experiment has demonstrated the instrument's ability to localize size-limited uranium anomalies.

A comparative study of different radiometric methodologies for the determination of 226 Ra in water

Abstract An evaluation of various radiometric methods to analyze 226 Ra in water has been employed on a set of 10 standard solutions of different concentrations in the range of 1–10 Bq/L −1 . The analysis was carried out using well-established procedures by means of gamma-ray, alpha-particle and liquid scintillation spectrometry. The feasibility of the various methods has been quantified in terms of relative standard error and percentage error. Correlations between the various methods have been presented and discussed. In general, good agreement was found in the results of various methodologies, which assures the accuracy of the methods and allows for the validation of instrumentation and procedures. Of the different methods adopted here, a combined procedure for the determination of 226 Ra along with 228 Ra using Quantulus 1220 ultra-low level background liquid scintillation counting gave the most accurate results.

Calibration and performance of a real-time gamma-ray spectrometry water monitor using a LaBr3(Ce) detector

A scintillation gamma-ray spectrometry water monitor with a 2″ × 2″ LaBr3(Ce) detector was characterized in this study. This monitor measures gamma-ray spectra of river water. Energy and resolution calibrations were performed experimentally, whereas the detector efficiency was determined using Monte Carlo simulations with EGS5 code system. Values of the minimum detectable activity concentrations for 131I and 137Cs were calculated for different integration times. As an example of the monitor performance after calibration, a radiological increment during a rainfall episode was studied.

Technology Update: Tool Enables Complete Cased-Hole Formation Evaluation, Reservoir Saturation Modeling

Technology Update For more than 40 years, the industry has used pulsed neutron logging to determine hydrocarbon and water saturations behind casing for reservoir management. Multiphase saturation measurements over time are useful for tracking reservoir depletion, planning workover and enhanced recovery strategies, and diagnosing production problems such as water influx and injection fluid breakthrough. Cased-hole logs also serve as a contingency when openhole logs cannot be run or are not considered for reservoir characterization. Although the cased-hole measurement suite has been greatly improved over many tool generations, the intrinsic physical measurements remained unchanged, which meant that operators could not obtain a complete picture of the rock and fluids behind casing. Input from openhole logs was required from a porosity or bulk density measurement for combination with the neutron porosity. Absent this input, primary formation evaluation in cased wellbores can be ambiguous. An additional challenge with cased-hole logging is correctly compensating for the effects of borehole fluids and the presence of completion hardware. Next-Generation Logs To meet the need for accurate surveillance in cased holes, Schlumberger recently introduced the Pulsar multifunction spectroscopy system. The system builds on innovative technologies originated by the company to provide the first complete cased-hole formation evaluation and reservoir saturation monitoring capability with openhole-equivalent measurements. This next generation in pulsed neutron logging integrates multiple detectors and a high-output pulsed neutron generator (PNG) to significantly improve measurement precision, data acquisition accuracy, and logging speed. The measurements are complemented by powerful algorithms that compensate for variation in the borehole fluids and completion in delivering robust, representative answers in complex conditions. The PNG and four detectors are housed in a 1.72-in.-outside-diameter (OD) tool that is designed for through-tubing access and logging through most completion restrictions. The detector adjacent to the PNG is the compact neutron monitor, which is primarily sensitive to fast neutrons to provide accurate and precise output measurement. There are three scintillation gamma-ray detectors for near, far, and deep detection. The near and far detectors use cerium-doped lanthanum bromide (LaBr3:Ce) scintillators, and the deep detector, farthest spaced from the PNG, has an yttrium aluminum perovskite scintillator. The three gamma-ray detectors are coupled to high-temperature-rated photomultiplier tubes, and their pulses are counted with specialized electronics matched to the high rate and resolution of the LaBr3:Ce scintillators.

Improved Scintillation Detector Performance via a Method of Enhanced Layered Coatings

Increasing demand for better detection performance with a simultaneous reduction in size, weight and power consumption has motivated the use of compact semiconductors as photo-converters for many gamma-ray and neutron scintillators. The spectral response of devices such as silicon avalanche photodiodes (APDs) is poorly matched to many common high-performance scintillators. We have developed a generalized analytical method that utilizes an optical reference database to match scintillator luminescence to the excitation spectrum of high quantum efficiency semiconductor detectors. This is accomplished by the fabrication and application of a series of high quantum yield, short fluorescence lifetime, wavelength-shifting coatings. We show here a 22% increase in photoelectron collection and a 10% improvement in energy resolution when applying a layered coating to an APD-coupled, cerium-doped, yttrium oxyorthosilicate (YSO:Ce) scintillator. Wavelength-shifted radio-luminescence emission and rise time analysis are also discussed.

Tl2LiYCl6: Large Diameter, High Performing Dual Mode Scintillator

Tl2LiYCl6:Ce (TLYC) is a recently discovered dual mode gamma-ray and neutron scintillator. So far small crystals of this composition have been studied, but for practical applications with affordable price, large-scale crystals are required. In this work, we present successful efforts to grow crack-free single crystals with sizes up to ⌀1″ × 5.5″. A variety of experimental techniques were employed to investigate the scintillation properties. A ⌀1″ × 1.2″ TLYC cylinder has a light yield of 25,000 ph/MeV, and its energy resolution is better than 4% at 662 keV. The gamma equivalent energy (GEE) produced by thermal neutron is 1.89 MeVee, along with a neutron induced light yield of 47,000 ph/n. Pulse shape discrimination (PSD) between gamma-rays and neutrons has been successfully shown with a current Figure-of-Merit (FOM) of 2.4. This article explores the crystal growth, scintillation properties, and potential applications of TLYC.

Ground level gamma-ray and electric field enhancements during disturbed weather: Combined signatures from convective clouds, lightning and rain

We report coincidences of ground-level gamma-ray enhancements with precipitation events and strong electric fields typical of thunderstorms, measured at the Emilio Segre Cosmic Ray observatory located on the western slopes of Mt. Hermon in northern Israel. The observatory hosts 2×2″ Nal(TI) gamma ray scintillation detectors alongside a vertical atmospheric electric field (Ez) mill and conduction current (Jz) plates. During several active thunderstorms that occurred near the Mt. Hermon station in October and November 2015, we recorded prolonged periods of gamma ray enhancements, which lasted tens of minutes and coincided with peaks both in precipitation and the vertical electric field. Two types of events were detected: slow increase (up to ~300min) of atmospheric gamma ray radiation due to radon progeny washout (or rainout) along with minutes of Ez enhancement, which were not associated with the occurrences of nearby CG lightning discharges. The second type showed 30min bursts of gamma rays, coinciding with minutes of Ez enhancement that closely matched the occurrences of nearby CG lightning discharges, and are superimposed on the radiation from radon daughters washed out to near surface levels by precipitation. We conclude that a superposition of accelerated high energy electrons by thunderstorm electric fields and radon progeny washout (or rainout) explains the relatively fast near surface gamma-ray increase, where the minutes-scale vertical electric field enhancement are presumably caused due to nearby convective clouds. Our results show that the mean exponential half-life depletion times of the residual nuclei produced during events without lightning occurrences were between ~25–65min, compared to ~55–100min when lightning was present, indicating that different types of nuclei were involved.

Energy-Dependent Scintillation Pulse Shape and Proportionality of Decay Components for CsI:Tl: Modeling with Transport and Rate Equations

In a spectroscopic gamma-ray scintillation detector, hot and thermalized transport, trapping, and recombination in multiple kinetic orders set the performance characteristics on which security, physics, and medical applications depend. CsI:Tl is the classic scintillator, yet even in it the details of these processes are still not fully understood. In this study, computational modeling reveals the origins of both recent and old observations about the spatial and temporal characteristics of the carrier interactions. This insight allows for improved material engineering of spectroscopic radiation detectors.

Li co-doped NaI:Tl (NaIL) — A Large Volume Neutron-Gamma Scintillator with Exceptional Pulse Shape Discrimination

We have demonstrated that Li can be substantially incorporated into the matrix of NaI under an optimized crystal growth process. The incorporation of Li introduces efficient neutron detection into an already successful commercial gamma-ray scintillator. Exceptional gamma-neutron pulse shape discrimination (PSD) has been demonstrated in Li co-doped NaI:Tl crystals with up to 8% Li concentration. Neutron-gamma PSD figure of merits are typically above 2 and can be high as 4.3 depending on the Li concentration. Gamma-ray performance of a single crystal Li co-doped NaI:Tl is on par with standard NaI:Tl. Simulations show that a $\varnothing ~50$ mm $\times50$ mm 6Li doped at 2% NaI:Tl detector has comparable neutron detection efficiency as a 6Li-enriched Cs2LiYCl6:Ce of the same size. High-temperature measurements have confirmed good gamma-neutron PSD to at least 160 °C. Creation of large volume (>1000 cm $^{3})$ , low cost, and dual-gamma spectroscopy/neutron sensitive detectors is possible with this technology.

New Developments in Scintillators for Security Applications

Radiation is an important part of security space: It is detected either passively in search of special nuclear materials or actively to monitor or interrogate objects of interest. Systems relying on radiation require adequate detectors. The most common radiation detectors are based on scintillating materials that convert hard (gamma, x-ray or neutron) radiation into visible light registered by a photodetector.The last decade has seen development of new materials driven by various security applications. This included the search for He-3 replacement technologies, which resulted in development of neutron sensing scintillators such as Ce-doped Cs2LiYCl6 (CLYC) or more recently Cs2LiLa(Br,Cl)6 (CLLBC). Since they are also good gamma-ray scintillators, they have also penetrated the detection market for passive dual-mode (gamma and neutron) detection systems, replacing scintillators such as NaI(Tl) or CsI(Tl) and competing with LaBr3(Ce). High-energy Non-Intrusive Inspection is another area where active research is being pursued in order to replace existing scintillator choices such as CdWO4, which is commonly used in simple radiography, and PbWO4, which is being studied for spectroscopic alternatives to radiography. For radiography, in particular, new ceramic scintillators such as Ce-doped GLuGAG (garnet) are considered, and for spectroscopy, Yb doped Lu2O3. In this paper we provide a short overview of these technologies.

Characterization of Environmental Radioactivity Level in Al-Basrah City (Iraq)

Soils and earth-derived building materials contain radioactive materials provide external exposure to nearby individuals and result in detrimental health effects including cancer. The risk of cancer incidence (morbidity) and mortality to individuals in Al-Basrah’s population (south of Iraq) related to external exposure to ambient gamma radiation is evaluated in this study. The risk estimations include delayed radiation effects (cancer morbidity, mortality and hereditary genetic damages). Radiation exposure rates were measured using BGS-4 gamma-ray scintillation (Scintrex, Canada) for the period 2012-2013. Absorbed dose rates in air and in human tissues are determined by applying typical conversion factors available in the literature. Age-dependent radiation dose is calculated for infants, children, and adults. Dose-to-risk conversion factors are applied to estimate potential risk to various body organs and tissues as a result of exposure to ambient gamma radiation. The findings of this study report that about 0.26% of Al-Basrah population are expected to be diagnosed with radiation-induced cancer over there lifetime. The lifetime fatal cancer probability (mortality) is found to be occurs at a rate of 0.19%. The risk of developing fatal stomach cancer is found to be occurs at a largest extent in comparison with other exposed body organs and tissues. Children and infants are found to be at a greater radiation risk than adults due to lower body weight. Other consequences of radiation injury such as genetic effects transmitted to succeeding generations are expected to occur at a rate of 0.03% in the offspring of Al-Basrah population as a result of changes transmitted via the genetic mechanisms due to irradiation of gonads.

Determination of oil–water volume fraction by using a pencil-beam collimated gamma-ray emitting source in a homogenized flow regime condition

The application of TPFHL as a novel two-phase flow Homogenizer loop in conjunction with the gamma-ray attenuation technique is emphasized. The capability of this instrumentation, to measure the volume fraction of iron ore powder-water two-phase mixture was demonstrated. In moving towards achieving the ability to use the above facility for two-phase mixtures with low density difference between phases, Monte Carlo (MC) simulations carried out to get the good geometry condition regarding to pencil-beam collimators used both for gamma-ray source and scintillation detector opposed it. Why of different types of oil compositions, it was used Normal-Decane (ND) as a good as well as a standard alternative to replace oil in oil–water experiments. In the following an optimum distance between a radioactive source and detector was achieved, which resulted in the maximum permissible accuracy for ND-water volume fraction measurements. Finally, different volume fractions of ND-water mixture were prepared and the corresponding fractions to each one were calculated.

Performance evaluation of newly developed SrI2(Eu) scintillator

The development of europium-doped strontium iodide (SrI2(Eu)) has attracted considerable attention, because of its excellent material properties as regards gamma-ray scintillator applications. These include its excellent energy resolution, high light output (>80,000ph/MeV), and high effective atomic number (Z=49). Here we report on the performance of ϕ 1in×1in SrI2(Eu) cylindrical crystals newly fabricated by Union Materials Inc. In this study, we measured the energy resolution and light output at 10 °C temperature intervals between −40 and 40°C, using an optically coupled 2-in photomultiplier tube (PMT) (Super Bialkali, Hamamatsu). The SrI2(Eu) light output increased by 0.12%/°C as the temperature decreased. At −40°C, we obtained the optimal energy resolution recording 2.91±0.02% full width at half maximum (FWHM) for 662keV gamma rays measured with 137Cs. For comparison, we also measured the same crystal using both a large-area (19×19mm2) avalanche photodiode detector (APD) and 8×8 multi-pixel photon counter (MPPC) arrays of 3×3mm2 pixels. The energy resolutions of 2.94±0.02%, 3.14±0.06% and 3.99±0.01% were obtained using PMT, APD, and MPPC, respectively, as measured at −20°C. We also measured the inherent background of SrI2(Eu) in a cave composed of Cu–Pb blocks with their thickness of 5–10cm confirming that SrI2(Eu) has an extremely low inherent background radiation. In this study, we have shown that SrI2(Eu) is a promising scintillator that can be utilized for radiation measurements incorporating low-energy X-rays to high-energy gamma rays, and can thus be applied in various medical, industrial, and environmental treatment fields in the near future.

Computation of full energy peak efficiency for nuclear power plant radioactive plume using remote scintillation gamma-ray spectrometry

A method of full energy peak efficiency estimation in the space around scintillation detector, including the presence of a collimator, has been developed. It is based on a mathematical convolution of the experimental results with the following data extrapolation. The efficiency data showed the average uncertainty less than 10%. Software to calculate integral efficiency for nuclear power plant plume was elaborated. The paper also provides results of nuclear power plant plume height estimation by analysis of the spectral data.

Partial ligand exchange as a critical approach to the synthesis of transparent ytterbium fluoride–polymer nanocomposite monoliths for gamma ray scintillation

A partial ligand exchange route to the preparation of transparent polymer nanocomposites with a high nanoparticle loading in bulk size for gamma-ray detection.