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The BIPM is developing a new service for international key comparisons in radionuclide metrology. The system, called ESIR, is based on a liquid scintillation counter using the Triple-to-Double Coincidence Ratio (TDCR) technique. The aim is to produce an international reference that can be reproduced over several decades of time in order to compare the calibration capabilities of National Metrology Institutes (NMIs). The maintainability of the electronics performing the signal processing is a challenge. To ensure the long-term sustainability of the electronics, the strategy is to set up redundant systems including at least one digital electronics module. The analogue modules developed in the 1990s and 2000s are less and less maintained and digital electronics are increasingly available on the market. In this context, a digitizer was tested and its suitability for the TDCR measurements compared to the currently used module based on an analogue front-end. This first implementation directly linking the photomultiplier anode to the CAEN digitizer without any analogue preconditioning shows a significant loss of detection efficiency and a lower signal to noise ratio observed on distributions of single photoelectrons. Although the TDCR method can correct for these efficiency losses, the loss of symmetry between the channels is too great to provide a sufficiently robust measurement. The use of low-pass filters upstream of the ADC will be considered to make this digital measurement system more reliable.

This chapter aims to emphasize the issue of the long-term stability of instruments used in metrology. This issue is a concern mentioned in the IEC/ISO17025:2017 standard and the JCGM100:2008 guide. Control charts are mentioned in these key documents as tools to assess whether a measurement process is under statistical control or not. Control charts (Shewhart charts, CUSUM chart, EWMA chart) are introduced and tested with simulated and real datasets from metrology instruments that operate at the ionizing department of the BIPM. The interest and the limits of such statistical analysis are discussed. They take their basis in a measurement model composed of Gaussian white noise. Although a measurement monitored over a relatively short period may be consistent with this model, it has been observed that the autocorrelation of the measurement data acquired over a long period limits the relevance of control charts. In this case, time series analysis seems more appropriate than conventional control charts. As an illustration, an optimal Bayesian smoother is introduced to demonstrate how to deconvolve the low-frequency random noise and refine the evaluation of uncertainty according to the measurement model for long-term measurement.

The digitalization of key comparisons in radionuclide metrology is being studied at the BIPM. Results of comparisons are made available on the BIPM KCDB platform where a PDF/A document can be downloaded. Access to the metadata contained in the PDF is not straightforward. Therefore, the XML and JSON versions of the report are now embedded in the PDF/A document, allowing direct access to the metadata. This achievement is a first step towards the implementation of FAIR (findable, accessible, interoperable, reusable) principles and does not affect the current policy of publishing comparison results. The combination of PDF/A and XML technologies seems to be an effective way to carry out digitalization. The strengths of both technologies can be brought together to meet the FAIR principles and ISO/IEC 17025 compliance. This approach benefits from robust data exchange features such as XML Schema and XML namespaces, as well as secure digital signatures and long-term archiving of PDF/A-3 documents.

Main text Since 1976, 30 laboratories have submitted 85 samples of 60Co to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), with comparison identifier BIPM.RI(II)- K1.Co-60. Recently, the PTB (Germany), the NIST (United States), the SMU (Slovakia), the BARC (India), the LNE-LNHB (France), the POLATOM (Poland), the ENEA-INMRI (Italy), the NPL (United Kingdom), the LNMRI-IRD (Brazil), the NMISA (South Africa) and the ANSTO (Australia) participated in the comparison and the key comparison reference value (KCRV) has been updated. The degrees of equivalence between each equivalent activity measured in the SIR and the updated KCRV have been calculated and the results are given in the form of a table. A graphical representation is also given. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Main text Since 2019, 2 laboratories have submitted 2 samples of 225Ac to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), with comparison identifier BIPM.RI(II)-K1.Ac-225. Recently, the POLATOM (Poland) participated in the comparison and a key comparison reference value (KCRV) has been calculated. For the first time, the degrees of equivalence between each equivalent activity measured in the SIR have been calculated and the results are given in the form of a table. A graphical presentation is also given. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

We report herein the synthesis of a new series of plastic scintillators (PSs) loaded with 6Li210B4O7 nanoparticles (NPs), as new radioluminescent sensors for fast/thermal neutron and gamma ray detection in the critical context of homeland security. This study aims to evaluate the benefit of such nanoparticles towards thermal neutron detection in a fast neutrons/gamma discriminating PS composition. First, a size-controlled synthesis of Li2B4O7 NPs assited with poly(N-vinylpyrrolidone) (PVP) is performed. Then enriched 6Li210B4O7 NPs (65 ± 22 nm) are dispersed in clear PSs mainly composed of polystyrene and standard fluorophores (20 wt% PPO, 0.03 wt% POPOP). For the first time, a triple nthermal/nfast/gamma discrimination is presented with a NP-loaded plastic scintillator, where both 6Li(n,α) and 10B(n,α) are observed.

International audience; MultiLayer Phoswich (MLP) scintillators have been studied for fission neutron detection by Monte-Carlo simulations and experimental tests. n/γ discrimination behavior of these systems and their angular dependencies have been characterized. The possibility to carry on a neutron counting system based of such an approach has been proven, and according to the results, an optimal thickness of layers for fission neutron counting was found around [100–150] μm. But, contrary to current liquid or solid-state discrimination scintillators, it appears that MLP-based neutron counting systems cannot directly classify neutron and gamma-ray interaction events from pulse shape analysis. To operate properly, it is therefore required to implement a compensation algorithm in the system readout.

The Bureau International des Poids et Mesures operates an international reference system (the SIR) to compare primary standards of radioactivity realized by National Metrology Institutes. Recently, the way of managing data relating to this system has been redesigned. The new model is fully integrated into the SI digital transformation initiated by the metrology community. The new approach automates the production of reports on the results from key comparison exercises for publication in the key comparison database, aiming to reduce the time needed to prepare reports without impacting quality. In operation for a year, the new system has produced 12 comparison reports within deadlines at a quality that meets the needs of the stakeholders in radionuclide metrology. The database and the software are controlled using the states-of-the-art Git version control system. In addition, thanks to the machine-readable database it produces, it paves the way for more digital data exchanges meeting the FAIR principles and directly accessible through a new application programming interface that is under development.

International audience; Fuel debris have a distinct neutron signature that can be detected to locate the said debris in a damaged nuclear power plant. Neutron measurement in a damaged PCV environment is however submitted to severe deployments constraints, including a high-dose-rate gamma background and limited available space. The study was therefore oriented towards small fission chambers (FC), with U-235-enriched active substrates. To investigate the expected performance of the FC in various irradiation conditions, a numerical model of the detector head was built. We describe the elaboration and experimental calibration of the numerical model and the Monte Carlo study of the fission rate inside U-235 coatings per generated neutron. The evaluation of a representative calibration coefficient then allowed us to carry out a multi-parameter performance study of a FC underwater, aiming at computing an explicit response function linking, on the one hand, the activity and spatial distribution of neutron emitters in a water container, with, one the other hand, the expected count rates measured by a fission chamber as a function of its radial and axial position inside the water volume. The FC underwater behavior was subsequently corroborated by a measurement campaign on a FC response, set at different positions inside a water drum, as a function of its axial and radial distance to a Cf-252 neutron source attached near the center of the container. We finally present an approach in which fuel debris localization is defined as an Inverse Problem, solvable with a Maximum-Likelihood Expectation Maximization (ML-EM) iterative algorithm. The projector matrix is built by capitalization on the results of the previously consolidated numerical studies. The ML-EM was tested on simulated data sets with a varying number of active voxels. Our first results indicate that, for a thermal neutron flux in the order of 10 n.cm−2.s−1 at the detector, originating voxels are identified with a spatial resolution in the radial plane in the order of 10 to 100 cm2.

International audience; This work aims at assessing the performance of a 235U enriched fission chamber in order to localize fuel debris, prior to dismantling operations, in a flooded primary containment vessel of a damaged nuclear reactor such as Fukushima Daiichi. Based on both a comprehensive scan of the environment and the detection of neutrons emitted by the melted core, fuel debris can be localized. In this paper, we carry out a simulation study using the MCNP6 code to investigate fission chamber response in the frame of fuel debris localization measurements in a damaged nuclear reactor. The CFUF34 fission chamber (manufactured by PHOTONIS) and the primary containment vessel of Fukushima Daiichi Unit 1 were chosen to conduct this work. Impact of different parameters were investigated with MCNP6, such as: neutron energy, water temperature, fission chamber position (altitude, lateral shift, and rotation), and sensitivity loss due to sediments potentially covering fuel debris. In summary, we show that fuel debris should be sought by their thermal neutron signature at a distance of a few centimeters and that potential rotational movements of the fission chamber up to 60° have a limited impact on signals measured. We also show that sensitivity loss due to sediments potentially covering fuel debris has been evaluated on the order of a factor 10 considering a 30 cm-thick sediment layer. On the other hand, experiments were performed to assess the impact of a strong gamma dose rate on fission chamber measurements. These irradiation trials involved a CFUE32 fission chamber (also manufactured by PHOTONIS) available in our laboratory and three different irradiation means: an X-ray tube, an 192Ir source, and a linear electron accelerator. These experiments enable to draw the conclusion that the fission chamber is not impacted by the gamma dose rate up to 104 Gy h−1, which is in good agreement with specifications provided by the manufacturer (PHOTONIS). In addition, no performance degradation was observed after an integrated gamma dose of 2200 Gy on the fission chamber in a 10 min irradiation. However, when the fission chamber is irradiated by gamma dose rates above 104 Gy h−1 (upper limit of the operating domain specified by PHOTONIS), a significant gamma background is observed. Nevertheless, as the gamma dose rates at Fukushima Daiichi should not exceed 103 Gy h−1, fission chamber measurements performed towards fuel debris localization in the primary containment vessels of the units would not be affected by the severe gamma-ray irradiation.

A bstract Fuel failures detection and monitoring is a key issue in sodium-cooled fast reactor operation. This detection is based on monitoring the signal of fission products using dedicated radiation monitoring systems based on gamma spectrometry or neutron counting. In this context, the French Alternative Energies and Atomic Energy Commission (CEA) investigates and developpes a Compton suppression system composed by a high-purity germanium diode, a bismuth germanate scintillator and a dedicated digital signal processing allowing filtering coincidences. This approach enables the Compton noise to be filtered without impacting the useful signal from short-lived radioisotopes. Through a calculation scheme based on a validated MCNP6 model of the detector. It was demonstrated that the sodium degassing is a mandatory option reducing the minimal detectable activities of fission products by a factor of up to 27. The Compton suppression system leads to an additional minimization of minimum detectable activities up to a factor of 4 enabling the ease measurement of the 89Kr safety indicator.

International audience; Radionuclide identification and quantification are a serious concern for many applications as for in situ monitoring at nuclear facilities, laboratory analysis, special nuclear materials detection, environmental monitoring, and waste measurements. High resolution gamma-ray spectrometry based on high purity germanium diode detectors is the best solution available for isotopic identification. Over the last decades, methods have been developed to improve gamma spectra analysis. However, some difficulties remain in the analysis when full energy peaks are folded together with high ratio between their amplitudes, and when the Compton background is much larger compared to the signal of a single peak. In this context, this study deals with the comparison between a conventional analysis based on “iterative peak fitting deconvolution” method and a “nonparametric Bayesian deconvolution” approach developed by the CEA LIST and implemented into the SINBAD code. The iterative peak fit deconvolution is used in this study as a reference method largely validated by industrial standards to unfold complex spectra from HPGe detectors. Complex cases of spectra are studied from IAEA benchmark protocol tests and with measured spectra. The SINBAD code shows promising deconvolution capabilities compared to the conventional method without any expert parameter fine tuning.

International audience; Neutron detection forms a critical branch of nuclear-related issues, currently driven by the search for competitive alternative technologies to neutron counters based on the helium-3 isotope. The deployment of plastic scintillators shows a high potential for efficient detectors, safer and more reliable than liquids, more easily scalable and cost-effective than inorganic. In the meantime, natural gadolinium, through its 155 and mostly 157 isotopes, presents an exceptionally high interaction probability with thermal neutrons. This paper introduces a dual system including a metal gadolinium core inserted at the center of a high-scale plastic scintillator sphere. Incident fast neutrons are thermalized by the scintillator shell and then may be captured with a significant probability by gadolinium 155 and 157 nuclei in the core. The deposition of a sufficient fraction of the capture high-energy prompt gamma signature inside the scintillator shell will then allow discrimination from background radiations by energy threshold, and therefore neutron detection. The scaling of the system with the Monte Carlo MCNPX2.7 code was carried out according to a tradeoff between the moderation of incident fast neutrons and the probability of slow neutron capture by a moderate-cost metal gadolinium core. Based on the parameters extracted from simulation, a first laboratory prototype for the assessment of the detection method principle has been synthetized. The robustness and sensitivity of the neutron detection principle are then assessed by counting measurement experiments. Experimental results confirm the potential for a stable, highly sensitive, transportable and cost-efficient neutron detector and orientate future investigation toward promising axes.

International audience; In order to meet clean core challenges in Sodium-Cooled Fast Reactors (SFR), specific attention is paid to the cladding integrity. To monitor this integrity, Delayed Neutron Detection (DND) systems are implemented. During clad failures, neutron precursor fission products (mainly halogens: I-137, Br-87, Br-88) escape into the primary coolant. The detection of these precursors through their delayed neutron emission ensures a diagnosis on clad failures events. In DND systems, He-3 proportional counters are selected as the best available technology for neutron detection purposes. Associated with He-3 counters, polyethylene blankets are required in order to thermalize neutrons. The first part of this study is dedicated to the optimization of the DND device by Monte-Carlo simulations in order to improve the detection capability. This optimization focuses on the device design presenting a graphite based alternative to polyethylene blankets in order to remove photoneutron noise from D-2(gamma,n) reactions in polyethylene in presence of a high Na-24 activity (emission of gamma rays at 2.75 MeV). The experimental part of this study is devoted to the validation of a measuring station including an He-3 counter with carbon for neutron moderation. Both Monte-Carlo simulations and experimental results highlight the potential for a low-noise DND system based on graphite moderation.

The primary vessel of a sodium-cooled fast neutron reactor (SFR) must remain free of any contaminant released by a cladding failure in a fuel assembly. A comprehensive detection system of cladding failures has then to be considered right from the beginning of the reactor design. One sub-system, called delayed neutron detection (DND), aims to search for delayed neutron precursors (DNP) through an ex-vessel analysis of a sodium sample, which goes to a container, usually named a pot, surrounded by neutron detectors. This paper presents a methodology to optimize the hydraulic part of the design of the DND detection block. From a detection scenario that identifies the physical parameters in play, a computational model is derived, which couples fluid mechanics and neutron transport. Different types of pot designs are considered, for which the sodium flow velocity, DNP concentration and detector activities are assessed. A new type of pot with a coil shape is proposed and shown to have the better performances with respect to the detector response to delayed neutrons.

International audience; Monitoring fuel integrity during sodium-cooled fast reactor operation becomes a crucial issue when sodium uranoplutonate formed consecutively to a clad aperture will foster cooling defaults. Delayed neutron detection (DND) systems are the key tools allowing to prevent and to mitigate such an accident by monitoring the concentration of delayed neutron precursors contained into the coolant. DND systems operate in hard gamma-rays fluxes and low-neutron activity levels. They have to be carefully optimized in order to detect, as early as possible, potentially harmful failures. A discussion is conducted on privileged ways to design DND systems, and some conclusions are stated.

Natural gadolinium displays a number of remarkable physical properties: it is a rare earth element, composed of seven stable or quasi-stable isotopes, with an exceptionally high magnetization and a Curie point near room temperature. Its use in the field of nuclear instrumentation historically relates to its efficiency as a neutron poison in power reactors. Gadolinium is indeed the naturally occurring element with the highest interaction probability with neutrons at thermal energy, shared between Gd-157 (15.65%, 254000 b cross section) and Gd-155 (14.8%, 60900 b) isotopes. Considering that neutron capture results in an isotopic change, followed by a radiative rearrangement of nuclear and atomic structures, Gd may be embodied not merely as a neutron poison but as a neutron converter into a prompt photon and an electron source term. Depending on the nature and energy of the reaction products (from a few-keV Auger electrons up to 8 MeV gamma rays) that the detector aims at isolating as an indirect neutron signature, a variety of sensor media and counting methods have been introduced during the last decades. This review first draws a theoretical description of the radiative cascade following Gd ( n , γ ) capture. The cascade may be subdivided into regions of interest, each corresponding to dedicated detection designs and optimizations whose current status is detailed. This inventory has allowed the authors to extract and benchmark key figures of merit for the definition of a detection scheme: neutron attenuation, neutron sensitivity (cps/nv), gamma rejection, neutron detection limit in a mixed field, intrinsic or extrinsic moderation, and transportability. On this basis, the authors have identified promising paths for Gd-based neutron detection in contemporary instrumentation.

International audience; The use of a room-temperature gamma spectrometer is an issue in environmental radiation monitoring. To monitor radionuclides released around a nuclear power plant, suitable instruments giving fast and reliable information are required. High-pressure xenon (HPXe) chambers have range of resolution and efficiency equivalent to those of other medium resolution detectors such as those using NaI(Tl), CdZnTe, and LaBr3:Ce. An HPXe chamber could be a cost-effective alternative, assuming temperature stability and reliability. The CEA LIST actively studied and developed HPXe-based technology applied for environmental monitoring. Xenon purification and conditioning was performed. The design of a 4-L HPXe detector was performed to minimize the detector capacitance and the required power supply. Simulations were done with the MCNPX2.7 particle transport code to estimate the intrinsic efficiency of the HPXe detector. A behavioral study dealing with ballistic deficits and electronic noise will be utilized to provide perspective for further analysis.

International audience; To monitor radioactivity emitted by a vehicle such as a pedestrian, a car, a train, or a truck, radiation portal monitors (RPMs) are commonly employed. It has been noted that these RPM suffer from a shadow-shielding effect when the source is transported by a dense and large vehicle such as a truck or a train. While methods using databases are listed as state of the art, we have developed an approach based on a state model, ensuring a gain in performance and flexibility. This new study presents a technique applied to RPM, efficiently compensating the shadow-shielding effect. A simulation study has been performed to highlight the efficiency and reliability of the method.

Animma 2017 : Liège, Belgique, 19th to 23rd 2017; International audience; Delayed neutron detection systems are key apparati in Sodium cooled Fast Reactors to prevent safety accidents. Based on the feedbacks from Phenix and Superphenix, DND systems are studied by means of the Monte-Carlo particles transport code MCNP6. Promising designs are proposed and investigated as a result of the simulation study.

International audience; The development of portable and personal neutron dosimeters requires compact and efficient radiation sensors. Gd-157, Gd-155 and Cd-113 nuclei present the highest cross-sections for thermal neutron capture among natural isotopes. In order to allow for the exploitation of the low and medium-energy radiative signature of the said captures, the contribution of gamma background radiation, falling into the same energy range, needs to be cancelled out. This paper introduces a thermal neutron detector based on a twin-dense semiconductor scheme. The neutron-sensitive channel takes the form of a Gd-covered CdZnTe crystal, a high density and effective atomic number detection medium. The background compensation will be carried out by means of an identical CdZnTe sensor with a Tb cover. The setting of a hypothesis test aims at discriminating the signal generated by the signature of thermal neutron captures in Gd from statistical fluctuations over the compensation of both independent channels. The measurement campaign conducted with an integrated single-channel chain and two metal Gd and Tb covers, under Cs-137 and Cf-252 irradiations, provides first quantitative results on gamma rejection and neutron sensitivity. The described study of concept gives grounds for a portable, online compatible device, operable in conventional to controlled environments.

Conference of 2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and Their Applications, ANIMMA 2013 ; Conference Code:102802; International audience; Radiological characterization of nuclear waste packages is an industrial issue in order to select the best mode of storage. The characterization becomes crucial particularly for waste packages produced at the beginning of the French nuclear industry. For the latter, available information is often incomplete and some key parameters are sometimes missing (content of the package, alpha-activity, fissile mass...). In this case, the use of non-destructive methods, both passive and active, is an appropriate solution to characterize nuclear waste packages and to obtain all the information of interest. In this article, we present the results of a complete characterization carried out on the TE 1060 block, which is a nuclear waste package produced during the 1960's in Saclay. This characterization is part of the DEMSAC (Dismantling of Saclay's facilities) project (ICPE part). It has been carried out in the SAPHIR facility, located in Saclay and housing a linear electron accelerator. This work enables to show the great interest of active methods (photon activation analysis and high-energy imaging) as soon as passive techniques encounter severe limitations.

International audience; To monitor radioactivity passing through a vehicle such as a pedestrian, a car, a train or a truck, Radiation Portal Monitors (RMP) are commonly employed. These detection systems consist of a large volume detector set close to the potential source path. An alarm is then triggered when the signal rises over a threshold initially estimated in view of the natural background signal. The approach developed in this work makes use of several detectors in a network along the source path. The correlation detection approach is elaborated to take into account the temporal periodicity of the signals taken by all distributed sensors as a whole. This new detection method is then not based only on counting statistics but also on the temporal series analysis. Therefore, a specific algorithm has been developed in our laboratory for this security application and shows a significant improvement, especially in terms of detection probability increase and false alarm reduction. This paper presents the theoretical approach and promising results obtained by simulation.

We report herein the application of a new series of plastic scintillators loaded with lithium tetraborate nanoparticles (Li 2 B 4 O 7 ) designed for the simultaneous detection of fast neutrons, thermal neutrons and gamma-rays. First, MCNP simulations are performed to highlight the potential benefit of Li 2 B 4 O 7 loading. Then, a nanoparticle-loaded scintillator is prepared and evaluated towards the detection of a partially thermalized neutron/gamma 252-californium source. Several scenarios of radiation/matter interactions are evaluated against the observed results. A detection chamber composed of boron-containing chipboard wood has been specifically designed and a subtraction method was set up to afford the best discrimination pattern. For the first time, a triple discrimination is presented with a nanoparticles-loaded plastic scintillator, where both 6 Li(n, α ) and 10 B(n, α ) signatures are observed. A Figure of Merit of 1.40 was calculated between fast neutrons and gamma rays around 480 keVee. The Figure of Merit between fast + thermal neutrons and gamma rays is slightly worse as it is 1.16 at 380 keVee.

International audience; Nuclear instruments such as alpha/beta contamination meter are frequently used in a compensated mode where the contribution of gamma radiation background is compensated by a guard detector. The signal of interest is then the subtraction of counting from both channels. In practice, the noise signal measured by the guard detector is not strictly equal to the noise contribution into the first detector due to anisotropic biases.The random error (under Poisson assumption) is taken into account to build a hypothesis test. The system is also designed to minimize the systematic error but in some cases, this bias could not be completely removed. The measurement system then shows different behavior when the surrounding environment changes exhibiting inopportune false alarms.A method allowing the false alarms to be suppressed is addressed in this study for compensated measurement. An improvement in terms of reliability has been proven.

International audience; Online nuclear counting represents a challenge due to the stochastic nature of radioactivity. The counting data have to be filtered in order to provide a precise and accurate estimation of the count rate, while ensuring a response time compatible with the application in view. An innovative filter is presented in this paper to address this issue. The filter is nonlinear and based on a Centered Significance Test (CST) providing a local maximum likelihood estimation of the signal. This nonlinear approach allows enables to smooth the counting signal while maintaining a fast response when brutal change in activity occurs. The filter is then improved by the implementation of a Brown's double Exponential Smoothing (BES). The filter has been validated and compared to other state-of-the-art smoothing filters. The CST* filter shows a significant improvement compared to all tested smoothing filters.

International audience; Gadolinium-covered modified plastic scintillators show a high potential for the deployment of cost-effective neutron detectors. Taking advantage of the low-energy photon and electron signature of thermal neutron captures in gadolinium-155 and gadolinium-157 however requires a background correction. In order to display a trustable rate, dual compensation schemes appear as an alternative to Pulse Shape Discrimination. This paper presents the application of such a compensation scheme to a two-bismuth loaded plastic scintillator system. A detection scintillator interacts with incident photon and fast neutron radiations and is covered with a gadolinium converter to become thermal neutron-sensitive as well. In the meantime, an identical compensation scintillator, covered with terbium, solely interacts with the photon and fast neutron part of incident radiations. After the acquisition and the treatment of the counting signals from both sensors, a hypothesis test determines whether the resulting count rate after subtraction falls into statistical fluctuations or provides a robust image of neutron activity. A laboratory prototype is tested under both photon and neutron radiations, allowing us to investigate the performance of the overall compensation system. The study reveals satisfactory results in terms of robustness to a cesium-137 background and in terms of sensitivity in presence of a californium-252 source.

International audience; Plastic scintillator loading with gadolinium-rich organometallic complexes shows a high potential for the deployment of efficient and cost-effective neutron detectors. Due to the low-energy photon and electron signature of thermal neutron capture by Gd-155 and Gd-157, alternative treatment to pulse-shape discrimination has to be proposed in order to display a count rate. This paper discloses the principle of a compensation method applied to a two-scintillator system: a detection scintillator interacts with photon and fast neutron radiation and is loaded with gadolinium organometallic compound to become a thermal neutron absorber, while a not-gadolinium loaded compensation scintillator solely interacts with the fast neutron and photon part of incident radiation. After the nonlinear smoothing of the counting signals, a hypothesis test determines whether the resulting count rate post-background response compensation falls into statistical fluctuations or provides a robust indication of neutron activity. Laboratory samples are tested under both photon and neutron irradiations, allowing the authors to investigate the performance of the overall detection system in terms of sensitivity and detection limits, especially with regards to a similar-active volume He-3 based commercial counter. The study reveals satisfactory figures of merit in terms of sensitivity and directs future investigation toward promising paths.

International audience; The synthesis, photophysical properties, and applications in scintillation counting of N-(2-ethylhexyl)carbazole (EHCz) are reported. This molecule displays all of the required characteristics for an efficient liquid scintillator (emission wavelength, scintillation yield), and can be used without any extra fluorophores. Thus, its scintillation properties are discussed, as well as its fast neutron/gamma discrimination. For the latter application, the material is compared with the traditional liquid scintillator BC-501 A, and other liquid fluorescent molecules classically used as scintillation solvents, such as xylene, pseudocumene (PC), linear alkylbenzenes (LAB), diisopropylnaphthalene (DIN), 1-methylnaphthalene (1-MeNapht), and 4-isopropylbiphenyl (iPrBiph). For the first time, an excimeric form of a molecule has been advantageously used in scintillation counting. A moderate discrimination between fast neutrons and gamma rays was observed in bulk EHCz, with an apparent neutron/gamma discrimination potential half of that of BC-501 A.

Nuclear counting is a challenging task for nuclear instrumentation because of the stochastic nature of radioactivity. Event counting has to be processed and filtered to determine a stable count rate value and perform variation monitoring of the measured event. An innovative approach for nuclear counting is presented in this study, improving response time and maintaining count rate stability. Some nonlinear filters providing a local maximum likelihood estimation of the signal have been recently developed, which have been tested and compared with conventional linear filters. A nonlinear filter thus developed shows significant performance in terms of response time and measurement precision. The filter also presents the specificity of easy embedment into digital signal processor (DSP) electronics based on field-programmable gate arrays (FPGA) or microcontrollers, compatible with real-time requirements. © 2001 Elsevier Science. All rights reserved.

In the current fuel cell modeling literature there is a gap between “physics-oriented” cell-level models and “application-oriented” system-level models. This paper presents a computational approach to close this gap by directly coupling cell-level and system-level simulation software. It allows to integrate a detailed description of electrochemistry and 2D transport into a system model within SIMULINK, allowing a direct feedback between system requirements and cell processes. By decoupling time scales between cell and system, the computational speed can be significantly enhanced. The method is applicable to both, polymer electrolyte fuel cells (PEFC) and solid oxide fuel cells (SOFC). Here, we show application in the context of PEFCs. Local membrane water management and electrochemical performance is made accessible on the system-level, where it can be used for visualization and control purposes.

We present here an elementary kinetic model of the electrochemical phenomena occurring in a polymer electrolyte membrane fuel cell (PEFC). Chemical degradation of the Nafion® membrane is described through a combination of OH radical formation via Fenton's reaction and a radical mechanism of side chain decomposition. At the electrodes, the model is coupled to a description of the hydrogen oxidation reaction, the oxygen reduction reaction, and the hydrogen peroxide formation reaction at the anodic side. We establish a first feedback between the evolution of structural properties of the membrane and its transport parameters (i.e., proton conductivity) for a fully humidified fuel cell. We assess the influence of the chemical membrane degradation on the cell performance and on macroscopic properties of the membrane (i.e., sulfonate site concentration).

In this paper we discuss a comprehensive physical-based model of the PEMFC materials degradation allowing predicting the MEA durability as function of the operation conditions, initial material loadings and electrodes microstructure. The approach, build within a modular multiscale non-equilibrium thermodynamics framework, couples atomistic-based descriptions of catalyst contamination/oxidation/dissolution/ripening, dissolved catalyst migration in the ionomer, C catalyst-support corrosion and chemical PEM degradation, with the degradation-induced nano/microstructural and transport properties (of reactants and charges) evolution. By describing the feedback between the instantaneous performance and the material aging phenomena, the model provides new insights on the competition between the different degradation processes under automotive-operating conditions. The predictive capabilities of our approach are illustrated in this paper through four applicative examples: 1) PtxCoy catalysts degradation 2) competition of PEM and cathode C degradation 3) synergies between anodic CO contamination and PEM and cathode C degradation, and 4) synergies between Pt and C degradation.

Correction for ‘Understanding the behaviour of different metals in loaded scintillators: discrepancy between gadolinium and bismuth’ by Guillaume H. V. Bertrand et al., J. Mater. Chem. C, 2015, 3, 6006.

Conference of 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, ANIMMA 2015 ; Conference Code:121554; International audience; Online nuclear counting represents a challenge due to the stochastic nature of radioactivity. The count data have to be filtered in order to provide a precise and accurate estimation of the count rate, this with a response time compatible with the application in view. An innovative filter is presented in this paper addressing this issue. It is a nonlinear filter based on a Centered Skellam Test (CST) giving a local maximum likelihood estimation of the signal based on a Poisson distribution assumption. This nonlinear approach allows to smooth the counting signal while maintaining a fast response when brutal change activity occur. The filter has been improved by the implementation of a Brown's double Exponential Smoothing (BES). The filter has been validated and compared to other state of the art smoothing filters. The CST-BES filter shows a significant improvement compared to all tested smoothing filters.

Conference of 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, ANIMMA 2015 ; Conference Code:121554; International audience; Plastic, scintillator loading with gadolinium-rich organometallic complexes shows a high potential for the deployment of efficient and cost-effective neutron detectors. Due to the low-energy photon and electron signature of thermal neutron capture by gadolinium-155 and gadolinium-157, alternative treatment to Pulse Shape Discrimination has to be proposed in order to display a trustable count rate. This paper discloses the principle of a compensation method applied to a two-scintillator system: a detection scintillator interacts with photon radiation and is loaded with gadolinium organometallic compound to become a thermal neutron absorber, while a non-gadolinium loaded compensation scintillator solely interacts with the photon part of the incident radiation. Posterior to the nonlinear smoothing of the counting signals, a hypothesis test determines whether the resulting count rate after photon response compensation falls into statistical fluctuations or provides a robust image of neutron activity. A laboratory prototype is tested under both photon and neutron irradiations, allowing us to investigate the performance of the overall compensation system in terms of neutron detection, especially with regards to a commercial helium-3 counter. The study reveals satisfactory results in terms of sensitivity and orientates future investigation toward promising axes.

Conference of 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, ANIMMA 2015 ; Conference Code:121554; International audience; Particle transport codes used in detector simulation allow the calculation of the energy deposited by charged particles produced following an interaction. The pulses temporal shaping is more and more used in nuclear measurement into pulse shape analysis techniques. A model is proposed in this paper to simulate the pulse temporal shaping and the associated noise level thanks to the output track file PTRAC provides by Monte-Carlo particle transport codes. The model has been dedicated to ion chambers and more especially for High Pressure Xenon chambers HPXe where the pulse shape analysis can resolve some issues regarding with this technology as the ballistic deficit phenomenon. The model is fully described and an example is presented as a validation of such full detector simulation.

Conference of 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, ANIMMA 2015 ; Conference Code:121554; International audience; Recent developments of plastic scintillators are reviewed, from January 2000 to June 2015. All examples are distributed into the main application, i.e. how the plastic scintillator was modified to enhance the detection towards a given radiation particle. The main characteristics of these newly created scintillators and their detection properties are given.

International audience; Organometallic chemistry has recently gained a lot of attention in the domain of plastic scintillators. Homogenously dispersed metal complexes in a polymer matrix can afford plastic scintillators with unseen abilities. Heavy atom loading is very attractive as it gives access to plastics with increased sensitivity towards elusive radiations such as gamma and neutron. But this comes with a drawback, as heavy atoms tend to quench fluorescence, hence decreasing the scintillation yield. We present here a comprehensive study of this phenomenon with bismuth and gadolinium complexes. We investigate the influence of the ligand nature by varying organometallic and fluorophore concentration to probe their interaction. We also propose an explanation of the difference in behavior between these two metals. These results were applied to the fabrication of large volume loaded plastic scintillators (>100 cm3). Bismuth loaded scintillators displayed characteristics equivalent to lead loaded commercial materials, and gadolinium samples proved to be able to capture thermal neutrons and release gamma rays.

International audience; This article presents the synthesis and the blend of bismuth complexes in polystyrene based plastic scintillators. A specific design has enabled the fabrication of a scintillator loaded with up to 17 wt% of bismuth. Tri-carboxylate and triaryl bismuth compounds were used to explore and understand the influence of bismuth loading on the two main criteria of plastic scintillation: light yield and detection efficiency of gamma-rays. For gamma radiation with an energy

Conference of 2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and Their Applications, ANIMMA 2013 ; Conference Code:102802; International audience; To monitor radioactivity passing through a pipe or in a given container such as a train or a truck, radiation detection systems are commonly employed. These detectors could be used in a network set along the source track to increase the overall detection efficiency. However detection methods are based on counting statistics analysis. The method usually implemented consists in trigging an alarm when an individual signal rises over a threshold initially estimated in regards to the natural background signal. The detection efficiency is then proportional to the number of detectors in use, due to the fact that each sensor is taken as a standalone sensor. A new approach is presented in this paper taking into account the temporal periodicity of the signals taken by all distributed sensors as a whole. This detection method is not based only on counting statistics but also on the temporal series analysis aspect. Therefore, a specific algorithm is then developed in our lab for this kind of applications and shows a significant improvement, especially in terms of detection efficiency and false alarms reduction. We also plan on extracting information from the source vector. This paper presents the theoretical approach and some preliminary results obtain in our laboratory.

Illegal radioactive material transportation detection, by terrorist for example, is problematic in urban public transportation. Academics and industrials systems include Radiation Portal Monitor (RPM) to detect radioactive matters transported in vehicles or carried by pedestrians. However, today's RPMs are not able to efficiently detect a radioactive material in movement. Due to count statistic and gamma background, false alarms may be triggered or at the contrary a radioactive material not detected. The statistical false alarm rate has to be as low as possible in order to limit useless intervention especially in urban mass transportation. The real-time approach depicted in this paper consists in using a time correlated detection technique in association with a sensor network. It is based on several low-cost and large area plastic scintillators and a digital signal processing designed for signal reconstruction from the sensor network. The number of sensors used in the network can be adapted to fit with applications requirements or cost. The reconstructed signal is improved by comparing other approaches. This allows us to increase the device speed that has to be scanned while decreasing the risk of false alarm. In the framework of a project called SECUR-ED Secured Urban Transportation - European Demonstration, this prototype system will be used during an experiment in the Milan urban mass transportation.

Conference of 2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and Their Applications, ANIMMA 2013 ; Conference Code:102802; International audience; Counting measurements associated with nuclear instruments are tricky to carry out due to the stochastic process of the radioactivity. Indeed events counting have to be processed and filtered in order to display a stable count rate value and to allow variations monitoring in the measured activity. Smoothers (as the moving average) are adjusted by a time constant defined as a compromise between stability and response time. A new approach has been developed and consists in improving the response time while maintaining count rate stability. It uses the combination of a smoother together with a detection filter. A memory of counting data is processed to calculate several count rate estimates using several integration times. These estimates are then sorted into the memory from short to long integration times. A measurement position, in terms of integration time, is then chosen into this memory after a detection test. An inhomogeneity into the Poisson counting process is detected by comparison between current position estimate and the other estimates contained into the memory in respect with the associated statistical variance calculated with homogeneous assumption. The measurement position (historical time) and the ability to forget an obsolete data or to keep in memory a useful data are managed using the detection test result. The proposed smoother is then an adaptive and a learning algorithm allowing an optimization of the response time while maintaining measurement counting stability and converging efficiently to the best counting estimate after an effective change in activity. This algorithm has also the specificity to be low recursive and thus easily embedded into DSP electronics based on FPGA or micro-controllers meeting "real life" time requirements.

Conference of 2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and Their Applications, ANIMMA 2013 ; Conference Code:102802; International audience; War against CBRN-E threats needs to continuously develop sensors with improved detection efficiency. More particularly, this topic concerns the NR controls for homeland security. A first analysis requires indeed a fast gamma spectrometry so as to detect potential special nuclear materials (SNM). To this aim, plastic scintillators could represent the best alternative for the production of large-scale, low-cost radiation portal monitors to be deployed on boarders, tolls, etc. Although they are known to be highly sensitive to gamma rays, due to their poor resolution, information relative to the nature of the SNM is tricky. Thus, only the Compton edge is obtained after interaction, and no information of the photoelectric peak is observed. This project concerns new developments on a possible pseudo-gamma spectrometry performed with plastic scintillators. This project is articulated on a combination of two developments: The design of new materials most suitable for recovering the photoelectric peak after gamma interaction with the scintillator. This work concerns mainly plastic scintillators loading with heavy elements, such as lead or bismuth. The analysis of the resulting signal with smart algorithms. This work is thus a pluridisciplinary work performed at CEA LIST and embeds 4 main disciplines: MCNPX simulations (simulated spectra), chemistry of materials (preparation of various plastic scintillators with different properties), instrumentation (lab experiments) and smart algorithms. Really impressive results were obtained with the unfolding of simulated spectra at various energies (from 241Am to 60Co) and an innovative approach was proposed to counter-balance the quenching effect of luminescence by heavy elements in plastic scintillators.

International audience; Reliability on simulation results is essential in nuclear physics. Although MCNP5 and MCNPX are the world widely used 3D Monte Carlo radiation transport codes, alternative Monte Carlo simulation tools exist to simulate neutral and charged particles' interactions with matter. Therefore, benchmark are required in order to validate these simulation codes.For instance, TRIPOLI-4.7, developed at the French Alternative Energies and Atomic Energy Commission for neutron and photon transport, now also provides the user with a full feature electron-photon electromagnetic shower. Whereas the reliability of TRIPOLI-4.7 for neutron and photon transport has been validated yet, the new development regarding electron-photon matter interaction needs additional validation benchmarks. We will thus demonstrate how accurately TRIPOLI-4's "deposited spectrum'' tally can simulate gamma spectrometry problems, compared to MCNP's "F8'' tally. The experimental setup is based on an HPGe detector measuring the decay spectrum of an $^{152}$Eu source. These results are then compared with those given by MCNPX 2.6d and TRIPOLI-4 codes.This paper deals with both the experimental aspect and simulation. We will demonstrate that TRIPOLI-4 is a potential alternative to both MCNPX and MCNP5 for gamma-electron interaction simulation.

Previous works on pressurized water reactors show that the nitrogen 16 activation product can be used to measure thermal power. Power monitoring using a more stable indicator than ex-core neutron measurements is required for operational sodium-cooled fast reactors, in order to improve their economic efficiency at the nominal operating point. The fluorine 20 and neon 23 produced by (n,α) and (n,p) capture in the sodium coolant have this type of convenient characteristic, suitable for power measurements with low build-up effects and a potentially limited temperature, flow rate, burn-up and breeding dependence. This method was tested for the first time during the final tests program of the French Phénix sodium-cooled fast reactor at CEA Marcoule, using the ADONIS gamma pulse analyzer. Despite a non-optimal experimental configuration for this application, the delayed gamma power measurement was pre-validated, and found to provide promising results.

This work deals with the use of gamma spectrometry for fourth generation Sodium Fast Reactor (SFR) power monitoring and clad failure detection. Usually, gamma spectrometers could not manage on-line applications in high count rate and fast activity variations but recent improvements in this research field may improve it. The ADONIS analyser for gamma spectrometry could met two needs of fourth generation SFR [1]. The ex-core neutron power measurement gives instant neutron power estimation but has some shift problems, mainly due to the burn-up phenomenon. High security margins are then set and so, the reactor can not work at its best thermodynamic efficiency. Previous works on Pressurized Water Reactors (PWR) show that gamma emitters concentration in primary coolant is also directly linked with reactor power (16N power measurement) [7]. On SFR, the use of short decay period gamma emitters as the 20F radionuclide will allow a fast power measurement with a direct correlation with the instant fission rate and without burn-up dependency. The second need is the clad failure detection improvement. The SFR clad failure detection is done by radiochemical and gamma measurements on argon cover gas and primary sodium samples. Gaseous fission products and delayed neutron fission products (only the 137I and the 87Br) are measured but lots of fission products (gamma emitters) are not measured nowadays on-line due to high sodium activity and its fast changes. This paper presents the experiment done at the French Phenix SFR of the CEA Marcoule and its analysis. Measuring activation and fission products contained in primary sodium coolant, the adaptive ADONIS gamma spectrometry system set on primary sodium coolant sample could be a new innovating power monitoring and clad failure detection system for future SFR.