Environmental Radiation Monitoring Research Articles

Crystal growth and Ce3+ concentration optimization in Tl2LaCl5: An excellent scintillator for the radiation detection

High effective atomic number (70) and density (5.17 g/cm3) among the known halide scintillators with excellent scintillation performance make Tl2LaCl5 (TLC) a new potential candidate for X- and γ-ray detection. The preliminary scintillation performance of TLC was reported earlier for small crystal pieces without any detail information of synthesis, crystal growth optimization conditions and Ce3+ doping concentration, which are investigated in this study. The newly developed melt rotation technique was found to be the best one for the synthesis of TLC and probably for other Tl-based compounds among the known melting techniques. Pure and nominal Ce3+ concentration of 1%, 3%, 5%, 7% and 10% TLC crystals were grown with two zones vertical Bridgman technique in two different type of homemade furnaces and found the optimum thermal gradient, pulling and cooling rate as 25 °C/cm, 0.5 mm/h and 20 °C/h, respectively. The best energy resolution of ∼3.3% (FWHM) and light yield of ∼82,000 ph/MeV were obtained for TLC:3%Ce3+ under 662 keV γ-rays excitation. The promising scintillation performance of TLC revealed that this crystal could be used in Positron Emission Tomography (PET), environmental radiation monitoring and homeland security applications.

Real-time acquisition and correction of temperature effect in NaI(Tl) detector-based environmental gamma radiation detection device

Environmental radiation monitoring especially around nuclear facility is needed to ensure public protection and safety. An online radiation monitoring system which continuously detects the presence of radioactive material in the environmental is important system to quickly detects uncontrolled radioactive released to the air. In this study, a radiation detection device based-on NaI(Tl) scintillation detector as part of an online radiation monitoring system has been developed and tested. During field testing, radiation count rate, and operational condition parameters which are temperature and relative humidity was collected continuously for 3 months. Data was transferred every 10 seconds with average communication delay around 0.57 second. Total number of data points is 733,725 records, and the average count rate was 653.09 cpm (σ = 81.77). Measured temperature is between 18.9 °C and 44.3 °C, while relative humidity is between 19.4 %RH and 78.6 %RH. Experimental result shows that count rate has temperature dependence. Effect of temperature to the count rate was estimated using power equation, and then the equation is used to correct the measurement data. After correction, several peaks which indicates the presence of radioactive material other than background radiation can be identified easily. In the future, further development such as radionuclide identification feature can be added to the prototype.

Design of fast digital spectrum stabilization method for UAV radiometry system

The drone radiation measurement system has a sharp increase in demand for environmental radiation monitoring due to its easy manoeuvrability, low aerial survey cost, high patrol efficiency and no personnel safety concerns. In order to adapt to the fast, flexible and efficient characteristics of the drone, the detector for the Unmanned Aerial Vehicle (UAV) radiation measurement generally consists of a plurality of small-sized detectors to form a detection array. Due to the low single crystal count rate and the influence of electronic system temperature and packaging, many detectors of the UAV radiation measurement system will have “spectral drifts”, which affects the quality of the synthesized spectrum and affects the accuracy of the whole system. Aiming at the characteristics of UAV spectrum measurement system, a three feature point recognition model is established, and the K-40 feature peak (1.46MeV) is approximated by reverse piecewise summation. Thus, the backscattering peaks and characteristic peaks K-40 of the measured spectrum can be obtained to achieve fast spectrum stabilization. Finally, through Gaussian Mixture Model (GMM) peak estimation and experimental validation, the method can obtain the characteristic peak position accurately, and the time between instrument start-up and automatic spectrum stabilization is less than 2 minutes.

Characterisation of borosilicate glass media as potential thermoluminescent dosimeters

Thermoluminescence dosimetry applications range from environmental radiation monitoring to sensing of the doses delivered in radiotherapy, through to verifying the doses of large-scale industrial irradiation. Particular utilisations largely depend upon the sensitivity of the dosimetric medium. In present work the thermoluminescent dosimetric properties of commercial low-cost borosilicate glass slides and glass-fibre filters were characterized, use being made initially of a 250 kV clinical therapy x-beam facility. From this, reproducibility and linearity were determined for radiation doses of 0.5, 1, 2, 4, 6, 8, and 10 Gy. Reproducibility of +/5% was obtained following appropriate screening, excellent linearity to dose also being demonstrated for both the borosilicate glass slides and glass-fibre filters, sufficient to demonstrate the potential of these media for use in radiotherapy dosimetry. Of note is the appreciable but not unsurprising dose response of the nominal 1.0 mm thickness borosilicate glass slides, with a per unit dose response some twice that of the less substantial glass-fibre filters. Further work has characterized the borosilicate glass slides for the megavoltage photons and electrons produced by linacs. A further potential interest results from the boron content, recognizing the associated appreciable neutron cross-sections. It is posited that the additional response observed at 10 MV over that at 6 MV is partly a result of photo-neutron production, a matter that is expected to form the basis of further investigations.

Evaluation of Scintillator Detection Materials for Application within Airborne Environmental Radiation Monitoring.

In response to the Fukushima Daiichi Nuclear Power Plant accident, there has occurred the unabated growth in the number of airborne platforms developed to perform radiation mapping—each utilising various designs of a low-altitude uncrewed aerial vehicle. Alongside the associated advancements in the airborne system transporting the radiation detection payload, from the earliest radiological analyses performed using gas-filled Geiger-Muller tube detectors, modern radiation detection and mapping platforms are now based near-exclusively on solid-state scintillator detectors. With numerous varieties of such light-emitting crystalline materials now in existence, this combined desk and computational modelling study sought to evaluate the best-available detector material compatible with the requirements for low-altitude autonomous radiation detection, localisation and subsequent high spatial-resolution mapping of both naturally occurring and anthropogenically-derived radionuclides. The ideal geometry of such detector materials is also evaluated. While NaI and CsI (both elementally doped) are (and will likely remain) the mainstays of radiation detection, LaBr3 scintillation detectors were determined to possess not only a greater sensitivity to incident gamma-ray radiation, but also a far superior spectral (energy) resolution over existing and other potentially deployable detector materials. Combined with their current competitive cost, an array of three such composition cylindrical detectors were determined to provide the best means of detecting and discriminating the various incident gamma-rays.

ESTABLISHMENT OF A LOW DOSE RATE GAMMA RAY CALIBRATION FIELD FOR ENVIRONMENTAL RADIATION MONITORING DEVICES.

For routine calibration of dosemeters used for environmental radiation monitoring, a low dose rate 137Cs gamma ray calibration field that fully satisfies the requirement of the ISO 4037 series was established in the Facility of Radiation Standards in Japan Atomic Energy Agency. Two different methods were employed to determine the reference air kerma rate, namely a conventional ionisation chamber and a G(E) function method used a newly developed scintillation spectrometer. To fulfil the requirement of the ISO 4037 and suppress scattering of Cs gamma ray within the room as far as possible, a suitable lead collimator was introduced to limit the irradiation area at test points and placed at the middle height in an irradiation room with a grating floor. From measured results of de-convoluted photon fluence spectrum and the variation of evaluated reference air kerma rates between 1.0 m and 3.0 m from the centre of the source, gamma ray scattering from the room structures was found to be negligible. The reference air kerma rate at distances between1.0 m and 3.0 m could be then interpolated by simply considering the inverse square law of the distance and air attenuation. The resulting Cs gamma ray calibration field could provide ambient dose equivalent rates of 0.7-7.2 μSv h-1 for use with environmental radiation monitoring devices. Finally, we attempted to calibrate a widely used NaI(Tl) scintillation survey metre, obtaining a quite satisfactory calibration factor. These results also imply that such survey metres can be employed to monitor affected areas and assess the progress of decontamination, as they can provide appropriate measurements of the ambient dose equivalent rate.

Establishment of a low dose rate gamma ray calibration field for environmental radiation monitoring devices.

Establishment of a low dose rate gamma ray calibration field for environmental radiation monitoring devices.

Low Dose Rate X-Ray Radiation Fields Implementation for Study of Energy Response of the Dosimeters Based on Scintillation Detectors

Near background low dose rate measurements are important part of the environmental radiation monitoring. It is possible to fulfill energy response verification for the high sensitive dosimeters based on inorganic scintillation detectors in low energy region when creating reference X-ray fields with dose rates up to 5 µSv/h. The aim of this work was to create and study reference X-ray fields with low dose rate and narrow spectrum in the energy range from 15 to 250 keV using high-purity metal filters as a part of X-ray irradiator of AT300 X-ray calibration facility.To determine the main characteristics of created X-ray fields highly sensitive comparators of photon radiation based on NaI(Tl) scintillation detectors was used. The comparators were developed in “ATOMTEX”. To verify comparators energy response the reference AT5350/1 dosimeter and ionization chamber TM32003 with sensitive volume 10000 cm3 were used.Characteristics of X-ray fields that were created on the AT300 X-ray calibration facility to verify the energy response of high sensitive dosimeters based on scintillation detectors were investigated. The possibility to calibrate high sensitive dosimetric measuring instruments based on scintillation detectors in the energy range up to 250 keV in X-ray beams was shown.

Overview of Radon Background Correction Technology for Airborne Gamma Spectrometry

In radiometric measurements, the radiation characteristics of radon and its daughters will increase the detection background value and affect the detection results. Research institutes in various regions of the world have studied the effects of radon and its daughters, and have done a lot of work according to the special climate, geological conditions and characteristics of radioactive events in their regions. In the view of the influence of radon background in airborne gamma-ray spectrometry measurement, this paper summarizes the research results of radon background correction in gamma-ray spectrometry measurement from three aspects in the world scope: environmental radiation monitoring, radiation monitoring instruments and nuclear emergency monitoring. In the aspect of environmental radiation monitoring, the research unit mainly considers the climatic factors such as rainfall, temperature and humidity, atmospheric and hydrological changes and seasonal changes, geological factors such as altitude, mineral types, and measurement means such as alpha measurement and inverse derivation gamma measurement. In terms of radiation monitoring instruments, radon and its daughters are mainly considered to reduce the impact and improve the measurement accuracy. In the aspect of nuclear emergency monitoring, the main consideration is how to improve the accuracy of measurement and avoid false alarm. On this basis, the research trend and development direction of radon background correction in airborne gamma-ray spectrometry are put forward.

Time Resolution of a Cs2LiYCl6:Ce3+ Detector Measured with a DRS4 Waveform Digitizer

The Cs2LiYCl6:Ce3+ (CLYC) scintillator is being widely employed in nuclear physics, planetary science, radiation environmental monitoring, nuclear security, and nonproliferation communities. The time resolution of a 1 × 1-in. CLYC scintillation detector is reported in this paper. It was measured by the use of a high sampling rate DRS4 waveform digitizer and an EJ-309 liquid scintillation detector. The digitizer was first characterized with regard to its intrinsic time resolution and then the time resolution of the EJ-309 detector was investigated. It served as a reference detector in the time resolution measurements for the CLYC detector. The time pick-off techniques used were the constant fraction discrimination and leading edge discrimination methods. In addition, the Savitzky-Golay filter was used to further improve the measured time resolutions. This filter was shown to be an effective approach to improving time resolution when the signal-to-noise ratio is low.

Universat-SOCRAT multi-satellite project to study TLEs and TGFs

We present concept of a new multi-satellite Universat-SOCRAT project aimed to study transient phenomena in the upper atmosphere such as transient luminous events (TLEs) and terrestrial gamma-ray flashes (TGFs). It is a new space project of Lomonosov Moscow State University based on the use of a few satellites in the near-Earth orbit for real-time monitoring of radiation environment, natural (asteroids, meteoroids) and artificial (space debris) potentially dangerous objects, electromagnetic transients including cosmic gamma-ray bursts, terrestrial gamma-ray flashes, and optical and ultraviolet bursts in the Earth’s atmosphere.Study of TLEs and TGFs remains an important and demanding task despite of a multitude of recently acquired data for these phenomena. This might be explained by the absence of comprehensive theoretical understanding of physical nature of high-energy processes in the Earth’s atmosphere. Multi-wavelength synchronous observations with moderate accuracy of localization of TGF and TLE events are necessary to gain an insight of physics governing these high-energy processes in the Earth’s atmosphere. In the article, we present results of TLE observations in space experiments of Moscow State University and discuss advanced instruments for optical observations of TLEs, as well as gamma-ray burst monitor and tracking gamma spectrometer for TGFs observations.

Sensor node for wireless radiation monitoring network

The structure of a sensor node for wireless network for environmental radiation monitoring is described in the article. The sensor node is developed on the base of semiconductor detector, modern microprocessor technology, and a last-generation telecommunications radio module. A new algorithm for measuring the power of the exposure dose of ionizing radiation has been investigated in the article. The amount of ionizing radiation energy absorbed by the human body affects the degree of radiation damage to its functional organs radically. In order to solve this problem we are working on improving the parameters of detectors, as well as the characteristics of electronic modules of detecting systems and creating software for controlling the detection process, collecting and processing information digitally, and presenting it properly to users in online mode. A wireless sensor network (WSN) is a distributed, self-organizing network of multiple sensors (sensors, motors, etc.) containing "Motes" (a specks of dust), so named because of the tendency to miniaturization and Executive devices combined with each other through the radio channel. The coverage area of such a network can range from several meters to several kilometers due to the ability to relay messages from one element to another. The motes usually contain battery-powered autonomous microcomputers (controllers) and transceivers. That allows the motes to self-organize into specialized networks, communicate with each other and exchange data. The role of human changes significantly in the model of sensor networks, since their elements – sensor microcomputers – become much more independent, often anticipating human requests long before they are received. "Homocentric" model of network computing with a human as a central link belongs to the past − a human moves from the center to the periphery and concentrates on the process managing, becoming a kind of an intermediary between the real world and computers.

Radiation distribution situation seven years after the Fukushima dai-ichi nuclear power plant accident and the leading edge of technology for environmental radiation monitoring

2011年に発生した福島第一原子力発電所事故から7年が経過しようとしている現在でも政府や自治体をはじめとする様々な環境中の放射線モニタリングが実施されている。原子力研究開発機構は，事故直後から有人のヘリコプターを用いた航空機モニタリングをはじめとする放射線モニタリングの実施主体となっている。本稿では，著者が関わっている事業を中心とした環境中での放射線モニタリングの現状についてまとめるとともに，避難指示区域における住民帰還の観点から生まれている新たなニーズと解決する新技術について紹介する。

DEVELOPMENT AND APPLICATION OF SOLID FORMS OF CaSO4:Dy THERMOLUMINESCENT DOSEMETERS IN RADIATION PROTECTION DOSIMETRY—A REVIEW

CaSO4:Dy is a reliable high-sensitive themoluminescent phosphor useful for low-level and high-level radiation measurements as it exhibits fading free linear dose response with a single glow peak at ~230°C in these dose regions. For large-scale radiation protection dosimetry service, it is embedded in Teflon matrix with varying thicknesses. Extensive studies have been carried out with such CaSO4:Dy Teflon discs in individual and environmental radiation monitoring applications including its capability to measure International Commission on Radiation Units and Measurements operational quantities. The review highlights their development and application in high-energy photon measurements, thin wafers and graphite-loaded Teflon discs for beta-dosimetry, phosphor-filled aluminium discs for high-dose applications, 6LiF-mixed CaSO4:Dy Teflon discs for thermal and albedo or moderated fast neutrons, sulphur-mixed CaSO4:Dy pellets for fast-neutron exposure even in the presence of gamma-rays and polyethylene-mixed CaSO4:Dy discs for fast neutrons.

Analytic simulator and image generator of multiple-scattering Compton camera for prompt gamma ray imaging.

For prompt gamma ray imaging for biomedical applications and environmental radiation monitoring, we propose herein a multiple-scattering Compton camera (MSCC). MSCC consists of three or more semiconductor layers with good energy resolution, and has potential for simultaneous detection and differentiation of multiple radio-isotopes based on the measured energies, as well as three-dimensional (3D) imaging of the radio-isotope distribution. In this study, we developed an analytic simulator and a 3D image generator for a MSCC, including the physical models of the radiation source emission and detection processes that can be utilized for geometry and performance prediction prior to the construction of a real system. The analytic simulator for a MSCC records coincidence detections of successive interactions in multiple detector layers. In the successive interaction processes, the emission direction of the incident gamma ray, the scattering angle, and the changed traveling path after the Compton scattering interaction in each detector, were determined by a conical surface uniform random number generator (RNG), and by a Klein-Nishina RNG. The 3D image generator has two functions: the recovery of the initial source energy spectrum and the 3D spatial distribution of the source. We evaluated the analytic simulator and image generator with two different energetic point radiation sources (Cs-137 and Co-60) and with an MSCC comprising three detector layers. The recovered initial energies of the incident radiations were well differentiated from the generated MSCC events. Correspondingly, we could obtain a multi-tracer image that combined the two differentiated images. The developed analytic simulator in this study emulated the randomness of the detection process of a multiple-scattering Compton camera, including the inherent degradation factors of the detectors, such as the limited spatial and energy resolutions. The Doppler-broadening effect owing to the momentum distribution of electrons in Compton scattering was not considered in the detection process because most interested isotopes for biomedical and environmental applications have high energies that are less sensitive to Doppler broadening. The analytic simulator and image generator for MSCC can be utilized to determine the optimal geometrical parameters, such as the distances between detectors and detector size, thus affecting the imaging performance of the Compton camera prior to the development of a real system.

Real‐time inverse distance weighting interpolation for streaming sensor data

AbstractWith advances in technology and an increasing variety of inexpensive geosensors, environmental monitoring has become increasingly sensor dense and real time. Using sensor data streams enables real‐time applications such as environmental hazard detection, or earthquake, wildfire, or radiation monitoring. In‐depth analysis of such spatial fields is often based on a continuous representation. With very large numbers of concurrent observation streams, novel algorithms are necessary that integrate streams into rasters, or other continuous representations, continuously in real time. In this article, we present an approach leveraging data stream engines (DSEs) to achieve scalable, high‐throughput inverse distance weighting (IDW). In detail, we designed and implemented a novel stream query operator framework that extends general‐purpose DSEs. The proposed framework includes a two‐panel, spatio‐temporal grid‐based index and several algorithms, namely the Shell and k‐Shell algorithms, to estimate individual grid cells efficiently and adaptively for different sampling scenarios. For our performance experiments, we generated several different spatio‐temporal stream data sets based on the radiation deposits in the Fukushima region after the nuclear accident of 2011 in Japan. Our results showed that the k‐Shell algorithm of the proposed framework produces a raster based on 250k observation streams in under 0.5 s using a state‐of‐the‐art workstation.

Application of a LaBr3(Ce) Scintillation Detector to an Environmental Radiation Monitor

To simultaneously determine the dose rate and radioactivity for detected gamma nuclides from one measured energy spectrum, the dose rate spectroscopy using a LaBr3(Ce) scintillation detector was first applied to an environmental radiation monitor, installed in the relative flat land at a height of about 1 m above the ground. After subtracting the intrinsic background of the LaBr3(Ce) detector used in the measured energy spectrum for count rate, that spectrum was converted into one for dose rate using the dose conversion factor. Several full-energy absorption peaks were then analyzed to calculate the individual dose rate for detected gamma nuclides, such as 214Pb, 214Bi, 228Ac, 212Pb, 208Tl, and 40K. The radioactivity of these nuclides distributed in the ground was calculated from their individual dose rates and conversion coefficients of the dose rate at 1 m above the ground into the radioactivity in the ground. The experimental verification was finally conducted by comparing the results of radioactivity using a portable high purity Ge (HPGe) detector and a LaBr3(Ce) detector equipped with the in situ objective counting system method and dose rate spectroscopy, respectively. Below, a 20% difference between two methods was shown in 214Bi, 228Ac, 208Tl, and 40K. In the case of 214Pb and 212Pb with low-energy photons, the calculated radioactivity using a LaBr3(Ce) detector was also within a 30% difference from those of an HPGe detector.

Radionuclide concentrations in sand samples from riverbanks of Muzaffarabad, Azad Kashmir

This paper presents the results of a radiological risk assessment arising from the presence of naturally occurring radionuclides in sand samples from three riverbanks in Muzaffarabad. The mean values obtained for 232Th, 226Ra, and 40K were found to be 44.58 ± 3.34, 48.25 ± 1.77, and 239.92 ± 22.73 Bq kg−1, respectively. To assess the uniformity of exposure, the radium equivalent activity (Raeq) was calculated and was found to be 130.47 ± 8.29 Bq kg−1. The current reported value for Raeq is lower than the maximum permissible value, that is, 370 Bq kg−1, and equivalent to a gamma dose of 1.5 mSv y−1. To investigate the possible contribution to health risks of alpha particle exposure, the radon exhalation rate (RER) from the sand samples was determined. The mean RER for all the samples was found to be 335 mBq m−2 h−1. About 43% of the samples were found to have an indoor excess lifetime cancer risk value slightly higher than recommended safety limit of 1, as proposed by the ICRP. A normalized parameter, the equivalent multiplicative factor, was defined and used to compare the current results with the findings of studies performed in other countries. Our findings are relevant to both human health and future environmental radiation monitoring.

Evaluation of Shiryaev-Roberts procedure for on-line environmental radiation monitoring

Water can become contaminated as a result of a leak from a nuclear facility, such as a waste facility, or from clandestine nuclear activity. Low-level on-line radiation monitoring is needed to detect these events in real time. A Bayesian control chart method, Shiryaev-Roberts (SR) procedure, was compared with classical methods, 3-σ and cumulative sum (CUSUM), for quantifying an accumulating signal from an extractive scintillating resin flow-cell detection system. Solutions containing 0.10–5.0 Bq/L of 99Tc, as T99cO4− were pumped through a flow cell packed with extractive scintillating resin used in conjunction with a Beta-RAM Model 5 HPLC detector. While T99cO4− accumulated on the resin, time series data were collected. Control chart methods were applied to the data using statistical algorithms developed in MATLAB. SR charts were constructed using Poisson (Poisson SR) and Gaussian (Gaussian SR) probability distributions of count data to estimate the likelihood ratio. Poisson and Gaussian SR charts required less volume of radioactive solution at a fixed concentration to exceed the control limit in most cases than 3-σ and CUSUM control charts, particularly solutions with lower activity. SR is thus the ideal control chart for low-level on-line radiation monitoring. Once the control limit was exceeded, activity concentrations were estimated from the SR control chart using the control chart slope on a semi-logarithmic plot. A linear regression fit was applied to averaged slope data for five activity concentration groupings for Poisson and Gaussian SR control charts. A correlation coefficient (R2) of 0.77 for Poisson SR and 0.90 for Gaussian SR suggest this method will adequately estimate activity concentration for an unknown solution.

Studies of ionizing radiation shielding effectiveness of silica-based commercial glasses used in Bangladeshi dwellings

Abstract Following the rapid growing economy, the Bangladeshi dwellers are replacing their traditional (mud-, bamboo-, and wood-based) houses to modern multistoried buildings, where different types of glasses are being used as decorative as well as structural materials due to their various advantageous properties. In this study, we inquire the protective and dosimetric capability of commercial glasses for ionizing radiation. Four branded glass samples (PHP-Bangladesh, Osmania-Bangladesh, Nasir-Bangladesh, and Rider-China) of same thickness and color but different elemental weight fractions were analyzed for shielding and dosimetric properties. The chemical composition of the studied material was evaluated by EDX technique. A well-shielded HPGe γ-ray spectrometer combined with associated electronics was used to evaluate the attenuation coefficients of the studied materials for 59 keV, 661 keV, 1173 keV and 1332 keV photon energies. A number of shielding parameters- half value layer (HVL), radiation protection efficiency (RPE) and effective atomic number (Zeff) were also evaluated. The data were compared with the available literature (where applicable) to understand its shielding capability relative to the standard materials such as lead. Among the studied brands, Rider (China) shows relatively better indices to be used as ionizing radiation shielding material. The obtained, Zeff of the studied glass samples showed comparable values to the TLD-200 dosimeter, thus considered suitable for environmental radiation monitoring purposes.