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A method to determine the cutoff diameter and counting efficiency of single-particle optical particle counters (OPC) is presented. An aerodynamic aerosol classifier (AAC) coupled with an atomizer was used to generate monodisperse dioctyl phthalate particles with a condensation particle counter (CPC) as the reference instrument. This method is accurate for capturing the counting efficiency of OPCs at lower size ranges and determining the cutoff diameter. The CPC was found to be a poor reference instrument for particles larger than 1 µm in which case an inkjet aerosol generator (IAG) was used as the monodisperse particle source and reference instrument. Two different particle materials were used with the IAG: lactose monohydrate and an ionic liquid (1-ethyl-3-methylimidazolium trifluoromethanesulfonate). A combination of the AAC to size smaller particles ( µm) and IAG to generate larger particles (>1 µm) was found to provide a comprehensive method capable of covering the counting efficiency over the entire operating range of OPCs. Copyright © 2020 American Association for Aerosol Research

We have developed a measurement method that enables accurate determination of the number concentration of liquid-borne particles by adopting simultaneous particle counting and mass measurement. The new measurement method consists of an optical particle counter (OPC) for particle counting, an electronic balance for mass measurement, a syringe pump for sampling, and a pulse height analyzer for signal processing. We refer to this method as the mass-measurement-type optical particle counting (M-OPC) method. The M-OPC method facilitates both metrological traceability of the mass of measured suspensions and evaluation of the counting efficiency of OPCs. Using the M-OPC method, we evaluated the measurement accuracy of two different types of OPCs: a light-scattering type and a light-extinction type. The validity of the measurement results obtained with the M-OPC method was examined by comparison with the results of an independent microscopic method using a scanning electron microscope (SEM). The M-OPC method also offers the possibility of calibrating the number concentration of particles in suspensions with diameters from the sub-micrometer to micrometer range by combining multiple OPCs. This method is expected to be used as the national primary standard at the National Metrology Institute of Japan of the National Institute of Advanced Industrial Science and Technology.

Beam hardening is a significant artifact that comes from the polychromatic nature of the X-ray source in computed tomography. It appears because the object tends to absorb more low-energy photons within the beam, which leads to a nonlinear relationship between attenuation and material thickness. As a result, the reconstructed image is spoiled. This work articulates an approach to promoting the correction of MeV X-ray beam hardening. In order to calculate the attenuation of the polychromatic beam, the following terms were evaluated: the energy spectra S(E) for sets of X-ray spectra with a maximum energy of 2, 4, 6 and 9 MeV were simulated using the Geant4 toolkit; the counting efficiency λ(E) was estimated based on the Lifton method; and the attenuation coefficient µ(E) was taken from the NIST database. The non-linear relationship between the attenuation and the thickness of iron was investigated. The beam hardening for each energy set was successfully corrected by polynomial fitting, transforming the polychromatic attenuation data into equivalent monochromatic data. The corrected attenuation was used to estimate the penetration capability of the X-ray source and produced a result that was consistent with what has been reported in the literature.

PURPOSE: Spectral distortion due to charge sharing (CS) and pulse pileup (PP) in photon counting detectors (PCDs) degrades the quality of PCD data. We recently proposed multi-energy inter-pixel coincidence counters (MEICC) that provided spectral cross-talk information related to CS. When PP was absent, the normalized Cramér–Rao lower bounds (nCRLBs) of 225-μm pixel PCDs with MEICC was comparable to those of 450-μm pixel PCD without MEICC. The aim of this study was to assess the performance of PCDs with MEICC at the presence of both CS and PP using computer simulations. METHODS: An in-house Monte Carlo program was modified to incorporate the following four temporal elements: (1) A pulse shape with a pulse duration of 20 ns, (2) delays of up to 10 ns in anode arrival times when photons were incident on pixel boundaries, (3) offsets proportional to a vertical separation between the primary and secondary charge clouds at the rate of ±4 ns per ±100 μm, and (4) a stochastic fluctuation of anode arrival times for all of the charge clouds with a standard deviation of 2 ns. We assessed the performance of five PCDs, (a)–(f), for three spectral tasks, (A)–(C): (a) The conventional PCD, (b) a PCD with MEICC, (c) a PCD with one coincidence counter (1CC), (d) a PCD with a 3×3 analog charge summing scheme (ACS), and (e) a PCD with a 3×3 digital count summing scheme (DCS); (A) conventional CT imaging with water (i.e., linear attenuation coefficient maps), (B) water–bone material decomposition, and (C) K-edge imaging with tungsten. The tube current was changed from 1 mA to 1,000 mA and the nCRLB was assessed. RESULTS: The recorded count rate curves were fitted by the non-paralyzable detection model with the effective deadtime parameter. The best fit was achieved by 25.8 ns for the conventional PCD, 18.6 ns for MEICC and 1CC, 140.5 ns for ACS, and 209.0 ns for DCS. The nCRLBs were strongly dependent on count rates. MEICC provided the best nCRLBs for all of the imaging tasks over the count rate range investigated except for a few conditions such as K-edge imaging at 1 mA. PP decreased the merit of MEICC over the conventional PCD in addressing CS. Nonetheless, MEICC consistently provided better nCRLBs than the conventional PCD did. The nCRLBs of MEICC were in the range of 49–58% of those of the conventional PCD for K-edge imaging, 45–76% for water–bone material decomposition, and 81–88% for the conventional CT imaging (i.e., linear attenuation coefficient maps). ACS provided better nCRLBs than the conventional PCD did only when the effect of PP was minor (e.g., when the counting efficiency of the conventional PCD was higher than 0.95 with the tube current of up to 100 mA). CONCLUSION: Besides a few cases, MEICC provides the best nCRLBs for all of the tasks at all of the count rates. ACS and DCS provides better nCRLBs than the conventional PCD does only when count rates are very low.

The sharing of charge between multiple pixels can significantly degrade the energy resolution of small pixelated compound semiconductor detectors. This paper describes an energy calibration and reconstruction technique to correct for absorbed energy that is split over two neighbouring pixels, defined as bipixel events. Results were obtained with a 1 mm thick CdTe detector with 250 µm pixel pitch and an inter-pixel spacing of 50 µm, using the STFC HEXITEC ASIC. The proportion of charge sharing events was found to be 54% for photons at 59.5 keV when applying a noise threshold of 3 keV. Across the energy range investigated, bipixels were the predominant shared event type and the absolute fraction of shared events was found to be dependent on the noise threshold used. The reconstruction technique described reduces the degradation of energy resolution due to charge sharing in bipixel events compared to simple charge sharing summing techniques. This improved counting efficiency compared to using only isolated events and improved energy resolution compared to pixel addition techniques. When only isolated pixels were included, a FWHM energy resolution of 1.42 keV at 140.5 keV was achievable; inclusion of bipixel events using pixel addition results in an energy resolution of 3.33 keV whereas the reconstruction technique described here results in an energy resolution of 2.14 keV. When bipixel events are combined with single pixel events, the number of counts within the 140.5 keV photopeak of 99mTc increased by over 100%.

This review discusses the developments in aerosol instrumentation that have led to the current vapor condensation based instruments capable of detecting sub-3 nm particles. We begin from selected r...

An international intercomparison was organized by Working Group 7, Internal Dosimetry, of the European Radiation Dosimetry Group in collaboration with Working Group 6, Computational Dosimetry, for measurement and Monte Carlo simulation of Am-241 in three skull phantoms. The main objectives of this combined exercise were (1) comparison of the results of counting efficiency in fixed positions over each head phantom using different germanium detector systems, (2) calculation of the activity of Am-241 in the skulls, (3) comparison of Monte Carlo simulations with measurements (spectrum and counting efficiency), and (4) comparison of phantom performance. This initiative collected knowledge on equipment, detector arrangements, calibration procedures, and phantoms used around the world for in vivo monitoring of Am-241 in exposed persons, as well as on the Monte Carlo skills and tools of participants. Three skull phantoms (BfS, USTUR, and CSR phantoms) were transported from Europe (10 laboratories) to North America (United States and Canada). The BfS skull was fabricated with real human bone artificially labeled with Am-241. The USTUR skull phantom was made from the US Transuranium and Uranium Registries whole-body donor (case 0102) who was contaminated due to an occupational intake of Am-241; one-half of the skull corresponds to real contaminated bone, the other half is real human bone from a noncontaminated person. Finally, the CSR phantom was fabricated as a simple hemisphere of equivalent bone and tissue material. The three phantoms differ in weight, size, and shape, which made them suitable for an efficiency study. Based on their own skull calibration, the participants calculated the activity in the three European Radiation Dosimetry Group head phantoms. The Monte Carlo intercomparison was organized in parallel with the measurement exercise using the voxel representations of the three physical phantoms; there were 16 participants. Three tasks were identified with increasing difficulty: (1) Monte Carlo simulation of the simple CSR hemisphere and the Helmholz Zentrum Munchen high-purity germanium detector for calculating the counting efficiency for the 59.54 keV photons of Am-241, in established measurement geometry; (2) Monte Carlo simulation of particular measurement geometries using the BfS and USTUR voxel phantoms and the Helmholz Zentrum Munchen high-purity germanium detector detector; and (3) application of Monte Carlo methodology to calculate the calibration factor of each participant for the detector system and counting geometry (single or multidetector arrangement) to be used for monitoring a person in each in vivo facility, using complex skull phantoms. The results of both exercises resulted in the conclusion that none of the three available head phantoms is appropriate as a reference phantom for the calibration of germanium detection systems for measuring Am-241 in exposed adult persons. The main reasons for this are: (1) lack of homogeneous activity distribution in the bone material, or (2) inadequate shape/size for simulating an adult skull. Good agreement was found between Monte Carlo results and measurements, which supports Monte Carlo calibration of body counters as an alternative method when appropriate physical phantoms are not available and the detector and source are well known.

The mechanical-collimation imaging is the most mature technology in prompt gamma (PG) imaging which is considered the most promising technology for beam range verification in proton therapy. The purpose of the present study is to compare the performances of two mechanical-collimation PG cameras, knife-edge (KE) camera and multi-slit (MS) camera. For this, the PG cameras were modeled by Geant4 Monte Carlo code, and the performances of the cameras were compared for imaginary point and line sources and for proton beams incident on a cylindrical PMMA phantom. From the simulation results, the KE camera was found to show higher counting efficiency than the MS camera, being able to estimate the beam range even for 107 protons. Our results, however, confirmed that in order to estimate the beam range correctly, the KE camera should be aligned, at least approximately, to the location of the proton beam range. The MS camera was found to show lower efficiency, being able to estimate the beam range correctly only when the number of the protons is at least 108. For enough number of protons, however, the MS camera estimated the beam range correctly, errors being less than 1.2 mm, regardless of the location of the camera. Keywords: Proton therapy, Beam range verification, Prompt gamma, Knife-edge camera, Multi-slit camera

In this study, we aimed to identify the reasons for track misrecognition caused by gamma-rays in the FNTD (fluorescent nuclear track detector) system. FNTDs were irradiated with fluence-controlled 241Am alpha-particles at 0°. The irradiated FNTDs were scanned by a commercial reader to obtain fluorescence images of uniform shape tracks and a reader-counted track density per unit area [mm−2]. The track density was good agreement with manually eye-counted track density. Then, the FNTDs irradiated with alpha-particles were additionally irradiated with 137Cs gamma-rays and scanned by the reader in order to monitor transition of the reader-counted track density with gamma dose. Track counting efficiency, which is defined as the reader-counted density divided by the eye-counted density, was reliable with until 33 mSv of gamma dose with ± 30% accuracy. However, with the higher dose of gamma-rays at 95 and 242 mSv, the efficiency fluctuated over the accuracy because of track misrecognition. To clarify the reasons for the track misrecognition, fluorescence track images were compared before and after gamma irradiations. On the fluorescence images with gamma-rays, the non-uniform signal caused by secondary electrons were observed (Sykora et al., 2010a). Especially with 242 mSv of gamma dose, the non-uniform signal formed “track-like” spots. To analyze the characteristics of the non-uniform signal, fluorescence intensity (FI) per pixel was analyzed for track and background (BG) areas separately. The FIs at both track and BG areas showed linearity to gamma dose. In the analysis of FI distributions, the fluctuation of FIs at BG area increased with gamma doses while the fluctuation of FIs at track areas did not change significantly. As a result, the difference of FI values between track and BG areas was smaller with the higher dose of gamma-rays. This phenomenon caused the difficulty of detecting tracks under gamma-ray exposure.

Multiple coincidence events from charge-sharing and fluorescent cross-talk are typical drawbacks in room-temperature semiconductor pixel detectors. The mitigation of these distortions in the measured energy spectra, using charge-sharing discrimination (CSD) and charge-sharing addition (CSA) techniques, is always a trade-off between counting efficiency and energy resolution. The energy recovery of multiple coincidence events is still challenging due to the presence of charge losses after CSA. In this work, we will present original techniques able to correct charge losses after CSA even when multiple pixels are involved. Sub-millimeter cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors were investigated with both uncollimated radiation sources and collimated synchrotron X rays, at energies below and above the K-shell absorption energy of the CZT material. These activities are in the framework of an international collaboration on the development of energy-resolved photon counting (ERPC) systems for spectroscopic X-ray imaging up to 150 keV.

In the framework of the development of future advanced treatment modalities in charged particle therapy, the use of silicon sensors is an appealing alternative to gas ionization chambers commonly used for beam monitoring. A prototype of a device, based on Low-Gain Avalanche Diode (LGAD) sensors with 50 μ m thickness, is being developed to discriminate and count single beam particles. This paper describes the design and characterization of ABACUS, an innovative multi-channel ASIC prototype for LGAD readout, based on a fast amplifier with self-reset capabilities. The design goals aim at detecting charge pulses in a wide range, from 4 fC to 150 fC, up to 70 MHz instantaneous rates, with a dead time of about 10 ns or less and efficiency larger than 98%. The characterization results indicate that even at the lowest input charge the signal-to-noise ratio is 15, high enough to keep full efficiency and preventing fake counts from the electronics noise. The dead time was found to be in the range between 5 ns and 10 ns, allowing to reach a full counting efficiency up to instantaneous rates of 70 MHz or larger, depending on the input charge.

This study presents the first reference calibrations of three commercially available bioaerosol detectors. The Droplet Measurement Technologies WIBS-NEO (new version of the wideband integrated bioaerosol spectrometer), Plair Rapid-E, and Swisens Poleno were compared with a primary standard for particle number concentrations at the Federal Institute for Metrology (METAS). Polystyrene (PSL) spheres were used to assess absolute particle counts for diameters from 0.5 to 10 µm. For the three devices, counting efficiency was found to be strongly dependent on particle size. The results confirm the expected detection range for which the instruments were designed. While the WIBS-NEO achieves its highest efficiency with smaller particles, e.g. 90 % for 0.9 µm diameter, the Plair Rapid-E performs best for larger particles, with an efficiency of 58 % for particles with a diameter of 10 µm. The Swisens Poleno is also designed for larger particles but operates well from 2 µm. However, the exact counting efficiency of the Poleno could not be evaluated as the cut-off diameter range of the integrated concentrator unit was not completely covered. In further experiments, three different types of fluorescent particles were tested to investigate the fluorescent detection capabilities of the Plair Rapid-E and the Swisens Poleno. Both instruments showed good agreement with the reference data. While the challenge to produce known concentrations of larger particles above 10 µm or even fresh pollen particles remains, the approach presented in this paper provides a potential standardised validation method that can be used to assess counting efficiency and fluorescence measurements of automatic bioaerosol monitoring devices.

The experimental characterization of an aged PIPS detector used in an alpha-particle spectrometry is performed using a standard mixed source of 238 U, 234 U, 239 Pu, and 241 Am. The variations in the detector efficiency and resolution (FWHM) at the main energy lines of the 238 U, 234 U, 239 Pu and 241 Am source were investigated at all possible source–detector distances under chamber air pressure of ∼ 1.33 Pa. Finding shows that on average, the counting efficiency data obtained from measurements are lower than those obtained by theoretical data and Monte Carlo simulation (SOLANG and AASI) methods. A combination of polymeric strippable coating and both traditional wiping and cleaning method for the detector decontamination works only show a significant reduction in the background activity. The counting efficiency improvement process by an increase of the higher voltages within the recommended range results in a good agreement in the counting efficiency comparison and a slight decrease of the detector dead layer thickness. Novel method to evaluate the dead layer thickness for PIPS detector via the variations in experimental energy loss with respect source to detector distance using alpha standard sources of 242 Pu has been proposed. This method can help to predict a default dead layer thickness value which will be as close as it was originally, is less than 50 nm from the manufacturer.

Gamma-ray scanning is a widely used technique for the non-destructive analysis of nuclear waste drums. This work proposes the use of a spectral index as an additional tool for data analysis. Under appropriate circumstances, it can be useful to assess the homogeneity of waste drums, to localize hot spots and to determine their counting efficiency. Experimental data for open geometry and segmented scanning systems are presented. No additional hardware is needed, as only gamma-ray spectra are needed.

This study introduces the method to evaluate the counting efficiencies of optical particle counters (OPCs), , at particle diameter greater than 1 μm by using an inkjet aerosol generator (IAG). This study demonstrates the evaluations at 5 and 10 μm in volume equivalent diameter. The chemical composition of the particles is either sodium chloride or lactose monohydrate. The aerosol flowrate of the IAG is set at 0.3 L/min, and the aerosol is delivered to an OPC with sampling flowrate 6 L/min (Omron, ZN-PD50S). The mismatch of the flowrates is compensated for by adding particle-free air in a laminar flow chamber. In order to simulate the sampling of uniformly mixed aerosol from a real environment, the particles are delivered to different points over the inlet plane of the isokinetic probe attached to the OPC. Particle flux into the isokinetic probe is proportional to the gas-velocity into the probe; however, the true velocity distribution is usually unknown. It is assumed that the true velocity distri...

Absolute measurement by the 4πβ-γ coincidence counting method was conducted by two photomultipliers facing across a plastic scintillator to be focused on β ray counting efficiency. The detector was held with a through-hole-type NaI(Tl) detector. The results include absolutely determined activity and its uncertainty especially about extrapolation. A comparison between the obtained and known activities showed agreement within their uncertainties.

The detection efficiency for large area alpha sources with adjustable heights of a raised lip around the edge were measured by 2 π gas-filled proportional counter. The variations in low-energy spectral shape were modeled using a Geant4 radiation and charge transport Monte Carlo simulation, to enable extrapolation of the spectrum to zero energy. COMSOL Multiphysics finite-element analysis was used to explore changes in the spectrum gain in the presence of a lip. It qualitatively reproduced an increase in peak height due to an increasing height of the source lip. A spectrum analysis procedure was developed to perform integral counting on sources with a lip. The experimental results were used to validate the model, which was then used to predict the changes in 2 π counting efficiency for other source-lip geometries.

PURPOSE: In radioimmunoassay (RIA), the gamma counter is the important instrument for the accurate measurement. To manage quality assurance of RIA, the counting efficiency of gamma counter is one of the important parameters. The aim of this study was to evaluate the counting efficiency of gamma counters in multiple institutes on the base of traceability by using the certified reference materials (CRMs). METHODS: Twenty-three institutes that perform RIA were enrolled in this study. I-125 CRMs that were certified by National Institute of Standards and Technology (NIST) were used. Each institute was asked to count the activity of I-125 CRMs at most twice on all gamma counters in use. The counting efficiency of each well of counter was calculated on the base of NIST-certified information, corrected for I-125 decay for date of testing. RESULTS: From 23 institutes, 44 gamma counters were evaluated. The average counting efficiency of all wells was 85.9% and the standard deviation was 13.5%. As a mean value of each gamma counter, three gamma counters showed poor counting efficiency (less than 70%). The poorest counting efficiency was 7%. The counting efficiency of seven gamma counters was between 70 and 75%. Eight counters had the counting efficiency between 75 and 90%. More than half of counter (26 gamma counters) showed excellent counting efficiency (more than 90%). The standard deviation variation range of inter-well efficiency was from 0 to 11.2. CONCLUSION: The first survey on the counting efficiency of gamma counter was performed in South Korea. Most of the RIA laboratories have well managed the quality assurance of gamma counter.

Gamma ray spectroscopy enables the identification of radioactive sources, and, with proper calibration, their activities. In use since the 1950s, NaI(Tl) spectroscopic systems remain popular due to their affordability and high detection efficiency. The crystals and accompanying electronics may vary, and there are practical choices necessary to produce the best possible spectra for a given application or correctly interpret system performance. An overview of the scintillation mechanism as well as the common features of a gamma ray spectrum are presented in this paper. This includes a discussion of the impacts of the size and shape of detector crystals on the spectrum and counting efficiency. A description of supporting electronics is included along with techniques for arranging and optimizing them. Coaxial cables become part of the circuit and can degrade the detector signal if they have mismatched impedance or excessive length. A discussion is included of tradeoffs involved in selecting combinations of individual electronics components for NaI(Tl) spectroscopic applications. Lastly, a comprehensive energy calibration procedure is provided. This paper thus serves as a tutorial on several practical aspects of a NaI(Tl) gamma ray spectroscopy system.

Based on the principle of Mie scattering, we design a small flow optical sensor of particle counter. Firstly, laser illumination system was simulated and designed by ZEMAX optical design software, and the uniform light intensity of photosensitive area was obtained. The gas circuit structure was also designed according to the related theory of fluid mechanics. Then, the method of combining with MIST scattering calculation software and geometric modeling was firstly used to design spherical reflection system, on the basis of the formula of object-image distance. Finally, the test was conducted after the optical sensor placed in self-designed pre-amplification and high-speed processing circuit. The test results show that the counting efficiency of 0.3 μ m gear is above 70%, 0.5 μ m gear and 1.0 μ m gear are both reached more than 90%, and the dispersion coefficient of each gear is very nearly the same, compared with the standard machine of Kanomax 3886 under the particle spraying flow of 2.5SCFH, 3.0SCFH, 3.5SCFH.

In this study, we present a traceable method for determining the counting efficiency of optical particle size spectrometers (OPSS), also known as aerosol spectrometers. The primary standard consists of an aerosol generation setup, a vertical flow tube for particle homogenization and a reference optical particle counter. The OPSS under testing and the reference optical particle counter sample aerosol simultaneously through specially designed isokinetic sampling probes at number concentrations ranging from 0.5 cm−3 up to several hundred particles per cm3 (depending on the particle size). Calibration in terms of particle size relies by convention on the use of certified PS (polystyrene) spheres in the size range 100 nm - 10 μm. Here, the counting efficiency profiles of two commonly used OPSS, namely the Model 3330 OPS (TSI Inc., USA) and the 11-D monitor (Grimm GmbH, Germany) are presented for the first time and discussed within the context of the ISO 21501–1:2009 and 21501–4:2018 standards on the calibration of OPSS for indoor/outdoor measurements and optical particle counters (OPC) for clean rooms applications, respectively. We believe that this study can help manufacturers improve the design of their instruments, contribute to the further development of relevant national and international standards and pave the way for a standardised and traceable calibration of OPSS units installed at air quality monitoring stations and industrial/workplace environments.

Radioiodine can be released in nuclear accidents and can cause internal contamination of the thyroid gland in members of the public. For population monitoring in radiation emergencies, measurement of counting efficiency is very important to accurately determine thyroid activity. Here, we estimate the counting efficiencies of a portable NaI detector using Monte Carlo simulations. Two different types of neck phantoms and a 7.62 cm long by 7.62 cm diameter NaI detector were modeled and the counting efficiencies were calculated depending on the thyroid size and distance from the neck phantom to the detector. We found that distance is a more important parameter than thyroid size. The optimal distance of the NaI detector from the neck surface was determined to be greater than 12 cm, beyond which the counting efficiency was not affected by thyroid size.

Background: Different cases exist in the measurement of thyroid radiobioassays owing to the individual characteristics of the subjects, especially the potential variation in the counting efficiency. An In situ Object Counting System (ISOCS) was developed to perform an efficiency calibration based on the Monte Carlo calculation, as an alternative to conventional calibration methods. The purpose of this study is to evaluate the applicability of ISOCS to thyroid radiobioassays by comparison with a conventional thyroid monitoring system. Materials and Methods: The efficiency calibration of a portable high-purity germanium (HPGe) detector was performed using ISOCS software. In contrast, the conventional efficiency calibration, which needed a radioactive material, was applied to a scintillator-based thyroid monitor. Four radioiodine samples that contained 125I and 131I in both aqueous solution and gel forms were measured to evaluate radioactivity in the thyroid. ANSI/HPS N13.30 performance criteria, which included the relative bias, relative precision, and root-mean-squared error, were applied to evaluate the performance of the measurement system. Results and Discussion: The portable HPGe detector could measure both radioiodines with ISOCS but the thyroid monitor could not measure 125I because of the limited energy resolution of the NaI(Tl) scintillator. The 131I results from both detectors agreed to within 5% with the certified results. Moreover, the 125I results from the portable HPGe detector agreed to within 10% with the certified results. All measurement results complied with the ANSI/HPS N13.30 performance criteria. Conclusion: The results of the intercomparison program indicated the feasibility of applying ISOCS software to direct thyroid radiobioassays. The portable HPGe detector with ISOCS software can provide the convenience of efficiency calibration and higher energy resolution for identifying photopeaks, compared with a conventional thyroid monitor with a NaI(Tl) scintillator. The application of ISOCS software in a radiation emergency can improve the response in terms of internal contamination monitoring.

International audience; In the case of a nuclear reactor accident the release contains a high proportion of iodine-131 that can be inhaled or ingested by members of the public. Iodine-131 is naturally retained in the thyroid and increases the thyroid cancer risk. Since the radiation induced thyroid cancer risk is greater for children than for adults, the thyroid dose to children should be assessed as accurately as possible. For that purpose direct measurements should be carried out with age-specific calibration factors but, currently, there is no age-specific thyroid phantoms allowing a robust measurement protocol. A set of age-specific thyroid phantoms for 5, 10, 15 year old children and for the adult has been designed and 3D printed. A realistic thyroid shape has been selected and material properties taken into account to simulate the attenuation of biological tissues. The thyroid volumes follow ICRP recommendations and the phantoms also include the trachea and a spine model. Several versions, with or without spine, with our without trachea, with or without age-specific neck have been manufactured, in order to study the influence of these elements on calibration factors. The calibration factor obtained with the adult phantom and a reference phantom are in reasonable agreement. In vivo calibration experiments with germanium detectors have shown that the difference in counting efficiency, the inverse of the calibration factor, between the 5 year and adult phantoms is 25% for measurement at contact. It is also experimentally evidenced that the inverse of the calibration factor varies linearly with the thyroid volume. The influence of scattering elements like the neck or spine is not evidenced by experimental measurements. © 2017 Institute of Physics and Engineering in Medicine.

A point source is used to investigate the effect of water phantom thickness and source-to-detector distance (SDD) on the sensitivity and counting efficiency of a rectangular detector gamma camera. The increase in water thickness resulted in an increase in scatter fraction, a decrease in sensitivity, and counting efficiency. The increase in SDD resulted in a decrease in sensitivity and an increase in counting efficiency. An SDD of 0.79±0.02 m is found to provide a good compromise for acceptable sensitivity and reasonable counting efficiency.

The interaction between analytes and the evanescent field of a waveguide can be exploited for highly sensitive measurement devices, which find already wide usage as chemical and biological sensors. Based on this sensor principle, we designed a single particle detector, featuring a silicon nitride waveguide with sub-micron dimensions, a diode laser, and a photodetector. The first prototype provides single counting efficiency for PSL spheres down to a diameter of 200 nm.

Photon-counting receivers are deployed on the NASA Ice, Cloud and land Elevation Satellite-2 (ICESat2) Advance Topographic Laser Altimeter System (ATLAS). The ATLAS laser altimeter design has total six ground tracks with three strong and three weak tracks. The strong track has nominally 4 times more laser power than the weak track. The receiver is operated in photon counting mode. There are 16 photon-counting channels for each strong track and 4 photon-counting channels for each weak track. Hamamatsu photomultiplier with a 4x4-array anode was used as photon counting detector. This receiver design has high counting efficiency (>15%) at 532 nm, low dark count rate (

An environmental radiation survey using a gamma-ray spectrometer is used to rapidly detect radioactive contamination over a wide area of ground that was released from nuclear events. For the successful application of a gamma-ray spectrometer to the calculation of the radioactivity concentration in the ground and the dose rate at 1 m above the ground, it is necessary to build a calibration procedure to obtain the counting efficiency at the in situ measurement, which means in situ calibration factor to report the calculation results from the measured net count rate according to the diverse detection geometries. This study is focused on the development of a program to calculate the in situ calibration factor and report the survey results in the environmental radiation surveys using three kinds of gamma-ray spectrometers, which have been widely used in the field of in situ measurements: a coaxial HPGe detector, cylindrical NaI(Tl), and rectangular NaI(Tl). The program is based on the results of diverse theoretical calculations of the unscattered photon fluence at the detector height, detector responses of three detectors, and their angular corrections. The developed program was successfully applied to the estimation of the radioactivity concentration of nuclides in the ground and the dose rate at 1 m height above the ground induced from them.

Measurements of airborne particles in buildings with low-cost optical particle counters (OPCs) are often inaccurate and subject to uncertainties. This study introduces a methodology to improve the performance of low-cost OPCs in measuring indoor particles through machine learning. A two-month field measurement campaign was conducted in an occupied net-zero energy house. The studied OPCs (OPC–N2, Alphasense Ltd.) report size fractionated concentrations from 0.38 to 17.5 μm. Co-located reference instrumentation included a scanning mobility particle sizer (SMPS: 0.01–0.30 μm) and an optical particle sizer (OPS: 0.30–10 μm). The machine learning field calibration method applies Gaussian Process Regression (GPR) and includes two components: (1.) correction of the size-resolved OPC counting efficiency from 0.38 to 10 μm and (2.) prediction of volume size distributions (mass proxy) below the 0.38 μm detection limit of the OPC. The field calibration method is applicable to OPCs that report size fractionated concentrations. In (1.), a GPR function was used to correct the size-resolved counting efficiency of the OPCs between 0.38 and 10 μm using the OPS as reference. In (2.), a second GPR function was used to predict the volume size distribution below 0.38 μm using the SMPS/OPS as reference. This was done given the significant contribution of sub-0.38 μm particles to volume concentrations in the accumulation mode. The machine learning field calibration method resulted in a significant improvement in the accuracy of size-integrated volume concentrations (PV2.5, PV10) reported by the OPCs as compared to the SMPS/OPS. Improvements were seen in the Pearson coefficient (before correction: 0.59–0.83; after correction: 0.98–0.99); coefficient of determination (before correction: 0.35–0.69; after correction: 0.97–0.98); and mean absolute percentage error (before correction: 35–69%; after correction: 19–25%).

The aim of this work is to present the method for sequential plutonium and americium activity determination in air filters using chromatographic radionuclide separation and alpha spectrometry measurement. The developed method may be employed for the purposes of workplace monitoring and as an indicator of the need of introducing the individual monitoring as well as a useful complementation of individual monitoring. Basic parameters describing the developed method such as values of chemical recoveries and minimum detectable activities for plutonium and americium isotopes have been determined. Applied counting efficiency was obtained using Monte Carlo calculation method.

A novel water-based condensation particle counter has been developed using a patented, single-flow mixing (SFM) condenser that permits a conventional thermal approach of using a hot saturator followed by a cold condenser to activate and grow particles for counting with an optical detector. A computational fluid dynamics (CFD) model of the internal flow, temperature, and vapor profiles was used to predict the effectiveness of the SFM condenser. Using the results from the CFD model, the counting efficiency was numerically calculated for pure water droplets, and the CPC cut-point (i.e., 50% counting efficiency) was predicted to be 8.3 nm. The experimental performance of the new CPC was measured with differential mobility analyzer-classified, monodisperse particles. The measured cut-points were 8.2 nm for Ag particles and 3.9 nm for NaCl particles. The reduction in the cut-point for NaCl is the result of a compound effect: water uptake by NaCl particles, which increases their size before entering into...

Direct 214Bi bioassays may elucidate some of the uncertainties related to the relationship between the ambient concentration of radon and its short-lived decay products and the corresponding radiation burdens of individual human subjects. Sequential total body 214Bi activity measurements were carried out on a group of 67 healthy adult volunteers living in a region with moderate airborne radioactivity and conducting similar daily activities using a whole-body counter equipped with sixteen NaI(Tl) detectors. The total body 214Bi activity in the studied subjects was related to gender, fat-free mass and the season of the year. Approximately 95% and 92% of the 214Bi activity measured during the cold seasons of the year in men and women, respectively, was attributed to radon progeny inhalation. Following acute exposure to high airborne radioactivity over a short time period, the 214Bi enhancement in a volunteer decreased exponentially with time post-exposure, with a half-time of about 40 min. Taking into account the anticipated low 214Bi activity in the vast majority of individuals, and the uncertainties in 214Bi biodistribution even during counting, accurate measurements can be obtained using high-sensitivity whole-body counters with almost geometrical invariant counting efficiency.

In vivo measurement is a main method of internal contamination evaluation, particularly for large numbers of people after a nuclear accident. Before the practical application, it is necessary to obtain the counting efficiency of the detector by calibration. The virtual calibration based on Monte Carlo simulation usually uses the reference human computational phantom, and the morphological difference between the monitored personnel with the calibrated phantom may lead to the deviation of the counting efficiency. Therefore, a phantom library containing a wide range of heights and total body masses is needed. In this study, a Chinese reference adult male polygon surface (CRAM_S) phantom was constructed based on the CRAM voxel phantom, with the organ models adjusted to match the Chinese reference data. CRAM_S phantom was then transformed to sitting posture for convenience in practical monitoring. Referring to the mass and height distribution of the Chinese adult male, a phantom library containing 84 phantoms was constructed by deforming the reference surface phantom. Phantoms in the library have 7 different heights ranging from 155 cm to 185 cm, and there are 12 phantoms with different total body masses in each height. As an example of application, organ specific and total counting efficiencies of Ba-133 were calculated using the MCNPX code, with two series of phantoms selected from the library. The influence of morphological variation on the counting efficiency was analyzed. The results show only using the reference phantom in virtual calibration may lead to an error of 68.9% for total counting efficiency. Thus the influence of morphological difference on virtual calibration can be greatly reduced using the phantom library with a wide range of masses and heights instead of a single reference phantom.

Time-integrated measurements of indoor radon levels are commonly carried out using solid-state nuclear track detectors (SSNTDs), due to the numerous advantages offered by this radiation detection technique. However, the use of SSNTD also presents some problems that may affect the accuracy of the results. The effect of overlapping tracks often results in the underestimation of the detected track density, which leads to the reduction of the counting efficiency for increasing radon exposure. This article aims to address the effect of overlapping tracks by proposing an alternative calibration technique based on the measurement of the fraction of the detector surface covered by alpha tracks. The method has been tested against a set of Monte Carlo data and then applied to a set of experimental data collected at the radon chamber of the Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, at the ENEA centre in Casaccia, using CR-39 detectors. It has been proved that the method allows to extend the detectable range of radon exposure far beyond the intrinsic limit imposed by the standard calibration based on the track density.

The possibility to determine internal activities of 252Cf in vivo in humans was studied by means of measurements of anthropomorphic phantoms. For this purpose, neutron capture by abundant hydrogen with subsequent emission of 2223 keV gamma radiation was used. The counting efficiency per emitted neutron for a 70 kg phantom was only 21% that for primary gamma radiation of the same energy. Detection limits were determined as 230 Bq and in a fictitious measurement chamber without background at the 2223 keV peak as 140 Bq. Several methods to enhance the measurement effect, all by capturing further neutrons outside the body by hydrogen or by cadmium, were investigated. The smallest activities that can be detected yield committed effective doses of 23 mSv and of 110 mSv if the results of the phantom measurements were adopted to adult humans and children, respectively.

FASTSCAN (Canberra, Meriden, CT, USA), a standing-type whole-body counter with upper and lower NaI(Tl) detectors, has been mostly used to determine local residents’ level of internal contamination with 134/137Cs following the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster in 2011. In the present study, we performed Monte-Carlo simulations with age-specific mathematical human phantoms to investigate the counting efficiencies of the FASTSCAN counter for 131I thyroid measurements. As a result, although the lower detector had low sensitivity for 131I in the thyroids of the adult and 15 y phantoms as well as the 10 y phantom standing on a 30-cm-high stool, the response of this detector may be used as an indicator of surface contamination overlooked on a subject. The total counting efficiency investigated in this study was 0.017–0.018 (cps/Bq) among all age groups. Based on this sensitivity, the determination level for thyroid activity could be calculated to be ~300 Bq under the slightly elevated background radiation level observed after the FDNPP disaster.

It is well known that synthetic diamond exhibits unique properties which make it an attractive material for a broad range of applications in the particle-detection field. In particular, thanks to its radiation hardness and availability in larger sizes, the polycrystalline (pc) diamond sample, grown by chemical vapour deposition (CVD), is especially suitable for online beam-monitoring applications, provided it demonstrates excellent counting performances. The present work reports the counting efficiency of a large 20.0× 20.0× 0.3 mm3 pcCVD diamond detector irradiated by 62 MeV/nucl. carbon beams. The parameter under study was estimated at different particle rates by employing a combination of different detector counters in a sandwich configuration. Results show a counting efficiency of ~ 95% up to 0.7 MHz particle rate. The pcCVD diamond detector under study was selected among other prepared devices by studying their leakage current and photocurrent characteristics under X-ray irradiation.

We report on an inter-laboratory comparison for the calibration of light-scattering optical particle counters measuring the number concentration of airborne particles in the size range 300 nm–5 µm. This comparison, registered as EURAMET pilot study Nr. 1453, is an important first step towards internationally recognized SI traceability in the measurement of low particle number concentrations encountered in clean-room facilities. The participating particle metrology laboratories of NMIJ (Japan), DFM (Denmark) and METAS (Switzerland) each provided a portable optical particle counter as a transfer standard to be circulated amongst the partners. The comparison covered particle number concentrations up to about 2 cm−3. The individual measurements for the transfer standards at each laboratory are in good agreement with the reference value, typically within 7%, which supports the applied national primary methods of measurement.

In case of a nuclear incident, a radioactivity level estimation is expected in a few hours for environmental samples. Liquid scintillation counting is a rapid technique to directly measure alpha and beta activities in aqueous samples. But main available commercial Liquid Scintillation Counters (LSCs) are too heavy and fragile to be used outside a laboratory. Thus the French Institute for Radiation protection and Nuclear Safety (IRSN) chose to develop their own LSC.The main objective was to develop a robust, light, small and easy-to-handle LSC taking into account quenching effects, able to measure energy spectrum, and discriminating alpha and beta particles. In order to get smaller and more robust LSCs, photomultiplier tubes (PMTs) were replaced by HAMAMATSU Multi-Pixels Photon Counters (MPPC®), also called silicon photomultipliers (SiPMs). The inconvenient of MPPC is their high dark noise compared to PMT which lead to a lower sensitivity for low energy beta emitters. But for our purpose, beta emitters of interest have high enough energies to be detected (e.g. 90Sr with a beta mean energy of 195.7 keV).First tests were performed with MPPC S13360-3050CS and S13360-3025CS to prove the measurement capabilities of such detectors. 14C standard, alpha and beta sources measurements were performed and gave a counting efficiency of a few percent. Thus such a technology is suitable for our purpose.

As part of the French radioactivity monitoring of drinking water, the gross alpha measurement takes an important place for rapid screening of the indicative dose. The evaporation method is commonly used in France because it is easier to perform and cost-effective, but the reproducibility is very poor (i.e. up to 40%). For this purpose, the Institute for Radiation Protection and Nuclear Safety (IRSN) propose to study the gross alpha measurement using Monte Carlo N-Particles (MCNP) calculations. In addition, a method using autoradiography has been developed for modeling realistic salt deposit. The model is able to predict the total efficiency with uncertainty considering all sources of variability in the gross alpha measurement. The model has been validated experimentally with a mean relative error of 6% for simulated detector counting efficiency and self-absorption correction factors. Comparison between simulated self-absorption curves made up with different radionuclides has demonstrated the area density should be limited to 2.5 mg.cm-².

Photon Counting (PC) efficiency has increased since the first photon counting devices. Third generation image intensifiers with high Quantum Efficiency (QE) photocathodes (of the order of 30%) are used with CCDs in intensified photon counting systems. But, the efficiency of this kind of camera is limited by the capability of the tube to transform an incoming photon into an electron and amplifying it so that the output signal is largely over the CCD Read-out Noise (RON). Improvements in CCD QE, which now reaches 90% at some wavelengths, and RON, as low as $3\overline{\mathrm{e}}$, have no effect on the total counting efficiency of these cameras. RON of $3\overline{\mathrm{e}}$ is still too high for an application such as photon counting for extreme faint fluxes. It is now possible to amplify the pixel signal into the CCD before it reaches the output amplifier and before it is affected by its noise. These Electron Multiplying CCD make it is possible to get sub-electron effective RON, low enough for PC. PC capability combined with a very low dark current, very good pixel response uniformity, and high QE offered by the CCD technology have made EMCCD the detector of choice for high-performance applications such as time resolved spectroscopy and low light imaging.

Liquid scintillation counting (LSC) is one of the most widely used methods for determining the activity of 241Pu. One of the main challenges of this counting method is the efficiency calibration of the system for the low beta energies of 241Pu (E max = 20.8 keV). In this paper we compare the two most frequently used methods, the CIEMAT/NIST efficiency tracing (CNET) method and the experimental quench correction curve method. Both methods proved to be reliable, and agree within their uncertainties, for the expected quenching conditions of the sources.

The examination of internal contamination is important for providing an adequate medical response during a radiological emergency. A whole-body counting system can assess gamma-emitting radionuclides in a human body when monitoring internal contamination. It is necessary to calibrate whole-body counting systems by using a calibration phantom, such as a Bottle Manikin Absorption phantom, to properly assess internal contamination. However, the total weight of the Bottle Manikin Absorber phantom is high, and there can be leakage of radioactive sources, which are disadvantages of using such a phantom. This study proposes a calibration phantom that is designed to overcome these disadvantages. The proposed phantom consists of rod sources that are inserted in each part of the phantom. The counting efficiency of the rod-source-inserted calibration phantom was acquired using a Monte Carlo simulation method, but the results were evaluated by comparing the experimental efficiencies with those of a conventional Bottle Manikin Absorption phantom by using two commercial whole-body counting systems (stand-up type and bed type). The efficiency curve of the rod-source-inserted phantom matched well that of the conventional calibration phantom. The relative deviation between the efficiencies of the conventional Bottle Manikin Absorption phantom and the proposed calibration phantom in both whole-body counting systems was less than 11%, and the total weight of the phantom was also reduced. These results suggest that the proposed phantom can be manipulated more easily and replace the conventional Bottle Manikin Absorption calibration phantom for these two types of whole-body counting systems.

In this work, the extrinsic counting efficiency and extrinsic sensitivity of a cylindrical source and a gamma camera with a rectangular detector were determined using homogeneous Tc-99(m). Scattered radiation effects were evaluated by both analyzing the energy spectrum of Tc-99m for the scatter fraction and plotting the extrinsic counting efficiency and sensitivity. It is found that the scattered fraction values increased with increasing source thickness. Calculated extrinsic sensitivity shows a gradually decreasing trend with increasing source thickness. The extrinsic efficiency decreases with increasing source thickness, It is concluded that increasing source to detector distances results with increasing extrinsic counting efficiency but decreasing extrinsic sensitivity.

Purpose Spatial resolution (SR) and counting efficiency (CE) are two pivotal parameters for Nuclear Medicine devices based on scintillation crystals. These parameters are in conflict with one another: the smaller the thickness of the scintillation crystal, the better (the worse) the resolution (the efficiency). In this work, a phoswich approach is reported, allowing devices to provide information optimized for both parameters. Methods In [1] , [2] a parameter to solve the Depth-of-Interaction (DoI) in scintillation detectors has been presented. As proved in [3] , it allows to distinguish the layer of a two-layers phoswich in which gamma-photons interact with the detector, too. The experimental response of a 50 × 50 mm2, 20 mm-thick, LYSO detector has been compared with a simulated detector of the same area based on two 10 mm-thick layers, coupled through optical grease (see Figure). Results The 20 mm-thick experimental detector exhibits a SR ranging from 2.85 (upper 10 mm) to 2.51 (lower 10 mm). With the proposed phoswich approach, the resolution improves up to 2.32 mm for the upper layer (again, 10 mm-thick) and 1.50 mm for the lower layer. With this approach, one can basically choose between the configuration showed in Table. Anyway, the phoswich approach improves the overall SR. Conclusions The proposed method, applied to phoswich detectors, allows to arbitrarily improve either CE or SR. The first is enhanced by selecting events from both layers, whereas the latter improves by selecting events from the lower layer.

A whole-body counter in SURO (NRPI) Prague, Czech Republic has been upgraded recently with the goal to enhance its capability of a safe, smooth, accurate and reproducible positioning of detectors for whole- and partial-body counting. The counter is intended especially for counting of low energy gamma emitters in various organs and tissues of the human body. Counting efficiency calibration of a four-detector system installed in the shielded room has been performed by means of physical and voxel phantoms. The consistency of in vivo bioassay data of three internal contamination cases long-term monitored in the Institute is shown.

In this study, an optical fiber detector was constructed by using a Ce:GAGG scintillator, optical fiber, and photomultiplier. The single crystal size of the scintillator was set to 3 × 3 × 20 mm after simulating the counting efficiency of gamma rays in the scintillator by using the MCNPX code. The constructed detector used the standard gamma ray sources Cs and Ba to measure radiation and analyze the spectral characteristics of gamma rays. The resulting trend curve showed excellent linearity with an R-squared value of 0.99741, and the detector characteristics were found to vary 2% or less with distance based on comparison with the MCNPX value. Furthermore, the spectroscopic analysis of the gamma ray energy from the single-ray and mixed-ray sources showed that Cs had its peak energy at 662 keV, and Ba had at 356 keV. It seems that if the fiber-optics detector is used, working hours and exposure of worker can be reduced.

Alpha particle spectrometry with collimation is a useful method for identifying nuclear materials among various nuclides. A mesh type collimator reduces the low energy tail and broadened energy distribution by cutting off particles with a low incidence angle. The relation between the resolution and the counting efficiency can be investigated by changing a ratio of the mesh hole diameter and the collimator thickness. Through collimation, a target particle can be distinguished by a PIPS ® detector under a mixture of various nuclides.

This work presents the development and first tests of a detector for continuous $^{222}$Rn in soil-gas measurements. It is based on scintillation spectrometry of $^{222}$Rn absorbed in scintillating polymers–plastic scintillator foils or plastic scintillation microspheres. The detector consists of an optical chamber optically coupled to a hermetic volume which contains small sized spectrometric components: a photomultiplier tube, high voltage supply, multi-channel analyzer and an outside board with chip-controlled sensors for pressure, temperature,humidity and an accelerometer. The detector is compact,portable and is designed for $^{222}$Rn in soil-gas in boreholes. Pilot laboratory studies of the performance of the detector are presented. They include: pulse-height spectrum characterization and energy resolution study with $^{239}$Pu source; counting efficiency study and study of the pulse-height spectrum of a plastic scintillator with $^{222}$Rn absorbed in it. The performance of the detector in the laboratory tests indicates that the approach to build a portable scintillation counter for $^{222}$Rn in soil-gas measurements in boreholes is feasible.