This study reports the first documented detection of 123Xe in the context of the CTBTO's International Monitoring System (IMS), in samples collected by the SPALAX-NG system (CEA/DIF, France). 123Xe is a short-lived radioisotope (T1/2 = 2.05 h) produced during medical 123I synthesis; atmospheric releases from medical facilities can lead to 123Xe capture by nearby IMS stations, potentially causing false 131mXe detections due to spectral overlaps in regions of interest (ROIs). Using high-resolution gamma and coincidence spectroscopy, we confirmed the presence of 123Xe and its decay product, 123I, in collected air samples. To mitigate interference, we developed an analytical adaptation for SPALAX-NG that identifies 123Xe via its 149 keV gamma peak and adjusts ROIs 5 and 6, with minimal efficiency loss (≤2.8%). This solution ensures accurate discrimination between 123Xe and CTBT-relevant isotopes. Our findings demonstrate the need to account for non-CTBT radioxenon isotopes in IMS analyses, particularly near medical isotope production sites, and advocate for high-resolution detection systems to improve monitoring reliability under the CTBT.

In the context of the Comprehensive nuclear-Test Ban Treaty, the CEA-DAM developed 10 years ago a system dedicated to the measurement of very low levels of particulate or gaseous fission products, named Gamma 3 . The system is composed of three high-resolution gamma-ray detectors (HPGe); low background noise is achieved through its optimized radiation shielding. Additional beta detectors, developed in the laboratory, can be integrated into the Gamma 3 for radioxenons samples. In addition to classical gamma spectrometry (1D), the Gamma 3 can operate in coincidence mode (2D) by detecting several particles in multiple detectors within a short time window. So far, the laboratory uses gamma/gamma and beta/gamma coincidences for qualitative purposes only. Algorithms have been developed to reconstruct coincidences from output list mode files. The low probability of coincidence events is compensated by high signal-to-noise ratio (a gain of 10 to 100 on direct spectrometry) and much lower detection limits. Difficulties come from the calculation of coincidence efficiencies needed to quantify activities. This work proposes a hybrid approach using Monte-Carlo simulations (MCNP) and experimental spectra to determine detection efficiencies in order to extract quantitative results from coincidence measurements. Simulation models have first been validated for direct spectrometry using radioactive sources; these validations ensure metrological connection between experiment and simulation. Then, coincidence detection efficiencies are retrieved from the Region Of Interest (ROI) method and used for the experimental results. Finally, this new method was tested using samples of fresh fission products.

Silver-exchanged zeolites are the most efficient materials for xenon adsorption at pressures in the ppm levels. It is widely accepted that silver moieties constitute the active phase in the adsorption. Among them, ZSM-5 appears to be the most efficient topology owing to its pore size and geometry. In this study, we fully exchanged seven different sodium-form zeolites (four ZSM-5, two BEA, and one MOR) to silver-form, characterized them, and compared their xenon adsorption capacities. Modeling the isotherms with a double-site Sips model allowed a quantitative comparison of their performances. The results confirmed a linear trend between the concentration of strong adsorption sites and the silver amount contained in the ZSM-5 and BEA zeolites. At the same time, it revealed that silver-exchanged MOR deviates from that trend and generates xenon adsorption sites in a higher-pressure range. Moreover, the Al-27 NMR measurements displayed a clear linear correlation between the amount of strong, silver-based, adsorption sites and the amount of exchangeable, framework aluminum-based, sites. Overall, this study revealed that an increase in the silver content leads to an increase in strong adsorption sites in a pressure range that depends on the zeolite structure. In addition, the tetra-coordination of aluminum must be checked to guarantee a high silver loading in pentasil-based zeolites.

The SPALAX-NG is a new-generation system that is designed to detect radioactive xenon at trace levels in the atmosphere following a nuclear explosion or civilian source release. This new system formed part of a validation program led by the Provisional Technical Secretary of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) Organization. In this study, the first SPALAX-NG unit was tested for six months between October 2018 and April 2019 at the CEA/DIF premises near Paris, France. This test period provided an outstanding opportunity to illustrate the high level of detectability and reliability of the system. The data availability obtained over this period was approximately 99%, which was well above the CTBT Data Availability criteria of 95%. The data reliability was demonstrated by a comparison with a collocated SPALAX-1 unit (former version of SPALAX) and by re-measuring several samples at the CTBT-certified French laboratory FRL08. The high sensitivity to the detection of the four relevant radioxenon isotopes was fully demonstrated and enabled the recording of a major dataset for western Europe. A large set of isotopic ratios was measured, which enabled the discrimination criteria between civilian sources and nuclear test signatures to be refined.

Atmospheric transport modeling has been used to interpret the unprecedented number of multi-isotope detections of radioxenons observed during the six months of the qualification process by the Comprehensive Nuclear-Test-Ban Treaty Organization of the new SPALAX-NG system (Système de Prélèvement Automatique en Ligne avec l'Analyse du Xénon - Nouvelle Génération). Highest 133Xe activity concentrations were found to be systematically associated with the concomitant measurement of several other radioxenons at the prevailing wind direction of north/northeast pointing to the Institute for Radio Elements (IRE), a medical isotope production facility located in Fleurus (Belgium). The lowest 133Xe activity concentrations were not associated with a prevailing wind direction or other radioxenons, indicating the contribution of distant sources (global background). The IRE's average source terms for 133mXe and to a lesser extent for 133Xe (slightly overestimated by a factor of 1.7) showed good agreement with the literature values, while corrections by a factor of ~23 and ~53 were proposed for 131mXe and 135Xe since the initial values were underestimated. However, detections of 131mXe alone and some low-activity concentrations of 133Xe associated with only one of the other radioxenons could not be linked to the IRE releases. Analysis of these cases suggests the contribution of local source releases that have been difficult to identify to date. In addition to the global background, releases from such local sources, if not identified, could affect the analysis of the isotopic ratios measured following a nuclear test. The characterization of these local contributions is now possible owing to the capacity of the SPALAX-NG and other new generation measurements systems.

New stability constants for NpV and PuV carbonates have been established by coupling capillary electrophoresis (CE) and ICP‐MS at the ionic strength of 0.202 mol/kgwater in NaClO4 and at various temperatures. The thermodynamic data [variation of the molar enthalpy, ΔrHm(T°) and entropy, ΔrSm(T) of reaction] associated with the formation of the AnO2CO3– (An = Np, Pu), AnO2(CO3)23–, and AnO2(CO4)35– complexes were determined. A drastic decrease in molar entropy was observed between the second and third complexes, suggesting important structural changes. Ab initio molecular dynamics showed that the 1:3 complex is formed with two carbonate ligands located at a shorter distance and one at a longer distance, suggesting that the closer ligands are coordinated in a bidentate fashion to the plutonyl(V) moiety whereas the third ligand is monodentate. The variation of the electrophoretic mobilities as function of charge/size ratio confirms unambiguously that the triscarbonate complex of pentavalent plutonium structurally differs from that of hexavalent plutonium where all carbonates anions are bidentate.

The development of gas separation processes dealing with very low concentration ranges is a rapidly growing domain with key applications such as trace detection, air purification from harmful pollutants, etc. Yet, the design of efficient technologies in this field is hampered by the lack of robust strategies to predict the gas selectivity of optimal adsorbents from simple pure gas adsorption data. Here, the selectivity predicted using different methods, namely Henry's method and the ideal adsorbed solution theory (LAST), are compared with the true selectivity obtained using breakthrough experiments. As a case study, these methods are discussed when applied to Xe/Kr separation in two different process conditions using different adsorbents (an active carbon and two silver-doped adsorbents). Typical data show that Henry's method, in which selectivity is assumed to correspond to the ratio of Henry's constant measured for each gas of the mixture, should be considered with caution as it is very sensitive to the pressure range considered but also the number of points used for affinity assessment. LAST is found to be more accurate provided its applicability to predict gas coadsorption from pure gas adsorption data is first established. However, even when applicable, the case of very low concentrations remains a problem as it leads to very large uncertainties in the selectivity predicted using LAST. We discuss how typical errors in assessing the selectivities using the different methods lead to nonoptimal adsorbent choices for a given separation process. Finally we demonstrate that Ag-loaded zeolite shows xenon capacities and Xe/Kr selectivities that surpass all other materials.

Silver nanoparticles are currently one of the most studied nanostructured nanomaterials. Because nanoparticle size and dispersion act together in determining a material’s physical and chemical properties, there is a continuous quest to develop size-controlled synthesis methods. Nonetheless, the instability of the nanometer-sized particles, which is caused by their tendency to aggregate irreversibly into larger particles, remains a recurrent problem. The use of confining scaffolds, such as the regular system of cages in a crystalline zeolite-type material, is often reported in the literature as an efficient solution to overcome particle migration at the surface. Silver nanoparticles encapsulated in ZSM-5 (Ag@ZSM-5) represent a new generation of adsorbent for Xe enrichment from the atmosphere that is currently being developed at the pilot scale in a Temperature Swing Adsorption (TSA) process. In this study, we have found that the presence of Cl-containing compounds in the air (VOCs) leads to a poisoning of the active silver phase by the formation of silver chloride. By a careful study of process parameters, we have found that most of the chlorine can be removed by heat treatment above 573 K so that the adsorption properties of silver are regenerated. That said, when applying 573 K temperature regeneration at the pilot scale, we observe a very minor but observable decay of xenon adsorption capacity that continues cycle after cycle. The mechanism of capacity decay is discussed in terms of (i) the residual presence of Cl at the surface of silver nanoparticles, (ii) the aggregation of silver nanoparticles into larger particles (sintering mechanism), and (iii) the acceleration of silver particle migration to the surface and sintering.

Silver metal nanoparticles are among the most widely studied nanoparticles. They are widely used heterogeneous catalysts used for many purposes such as antisepsis, hydrogenation, and carboxylation but also for the trapping of xenon in nuclear test and detection facilities. The catalytic activity and adsorption capacity of silver nanoparticles, which depend on their size distribution and dispersion on the support, generally decrease with time because of agglomeration of the metal into larger particles. In this study, we quantified the sintering process of silver nanoparticles supported in Zeolite Socony Mobil 5 (ZSM-5) zeolite. It was found that 85% of the sintering process of the silver nanoparticles was driven by Ostwald ripening. We found that silver nanoparticles are trapped in porous cavities that are meso- or macroporous defects in the zeolite. Although this phenomenon limits the amount of silver that diffuses to the zeolite external surface, it does not prevent the formation of large particles by atom migration. The presence of chloride reactants facilitates the sintering phenomenon by lowering the energy barrier. This finding provides a rational basis for the design of silver-containing zeolite-based heterogeneous catalysts.

Lessons-learned from 10 years of noble gas stations operation and dedicated R & D allowed the design of a New Generation of station. In order to produce 60 m(3) air equivalent Xenon samples every 8 h, it implements: (i) larger sampler unit for Xenon extraction (2 compressors and 8 nitrogen membranes), (ii) new noble gas adsorbent (Ag@ZSM5), (iii) hardened components and (iv) new high resolution coincidence low background spectrometer (HPGe/PIPSBox). Station expected radioxenon sensitivity is lower than 0.3 mBq/m(3).

Radon (222Rn), a radioactive gas with a half-life of 3.82 days, is continuously emanated from soil, rocks, and water by the radioactive decay of 226Ra. Radon-222 is released from the ground into the atmosphere, where it is transported mainly by turbulent diffusion or convection. For precise measurement of radon-222 atoms in the atmosphere, the detectors typically used present a small volume or surface area and are therefore not very sensitive, especially for online measurements and short sample intervals (<1 h). This article deals with the development of a Highly Sensitive Radon Amplifier (HiSRA) consisting in an enrichment system placed prior to a classic radon-222 analyzer. This system uses permeation membranes that make it possible to treat large quantities of air online (30 m3 h-1). The radon-222 concentration is increased instantaneously by at least a factor of 30 across the HiSRA system. Therefore, in this study, when coupling to an ionization chamber (AlphaGUARDTM) at the outlet of the HiSRA system, the detection limit of the overall system is multiplied by factor of 30 and induces a new LD for a radon 222 gas analyzer lower than 1 Bq m-3 for an integrating time of 10 min and 0.1 Bq m-3 for 1 h. We constructed one radon amplifier prototype that provided the preliminary results for amplification efficiency and the initial measurements presented herein.

Although thermodynamics of AnIVDTPA− (DTPA = diethylenetriaminepentaacetic acid) complexation have been reported for 50 years, reliable data at low ionic strength is still missing.

Experiment and molecular simulation are used to investigate adsorption in heterogeneous porous media consisting of hierarchical solids (combining different porosity scales) or composite solids (such as silver nanoparticles adsorbed at the external surface of zeolite). It is shown that adsorption in such heterogeneous materials can be written as a linear combination of the adsorption isotherms in its different domains (i.e. porosity scales for the hierarchical sample and constituents for the composite sample). In the case of the composite material, we also show that the linear combination can be used with weighing parameters obtained for a different adsorbate. Such a superimposition principle, which is validated using well-characterized experimental samples, is of interest for characterization purpose as well as industrial applications as they can be used to determine accurately the amount of phases in a given sample (volume corresponding to a given porosity scale or constituent). In contrast, significant departure between the experimental adsorption isotherm and the linear combination can be used to detect coupling effects between the different domains or restrained access to a given domain type. Such a characterization strategy of complex heterogeneous media is complementary to other experiments, such as those probing capillary hysteresis shapes, scanning curves and subloops, which allow determining the distribution of domains within the framework of the independent domain theory.

Rare gas capture and purification is a major challenge for energy, environment, and health applications. Of utmost importance for the nuclear industry, novel separation processes for Xe are urgently needed for spent nuclear fuel reprocessing and nuclear activity monitoring. The recovered, non-radioactive Xe is also of high economic value for lighting, surgical anesthetic, etc. Here, using adsorption and breakthrough experiments and statistical mechanics molecular simulation, we show the outstanding performance of zeolite-supported silver nanoparticles to capture/separate Xe at low concentrations (0.087-100 ppm). We also establish the efficiency of temperature swing adsorption based on such adsorbents for Xe separation from Kr/Xe mixtures and air streams corresponding to off-gases generated by nuclear reprocessing. This study paves the way for the development of novel, cost-efficient technologies relying on the large selectivity/capacity of adsorbent-supported silver nanoparticles which surpass all materials ever tested.

A new RIS-TOF instrument, called FAKIR (Facility for Analyzing Krypton Isotope Ratios), has been developed at CENBG in order to measure Kr isotope ratios with an extremely high sensitivity.

A double focusing sector field mass filter used in Nier-Johnson geometry has been built in order to perform Kr isotope enrichment for 81 Kr and 85 Kr isotopes. The principle consists in implanting Kr+ ions accelerated at 7 keV in Al foils after separation using the magnetic sector. A specific ion source has been designed capable of generating high Kr+ ion beams (>0.5 μA) to transfer into the collecting Al foils in 3 to 5 h significant fractions of large Kr samples (1015 to 1016 atoms) initially introduced in the instrument. Implanted Kr isotopes can be further selectively released from the Al foil by surface ablation using an infrared laser beam. Implantation yields and enrichment factors are measured using a conventional mass spectrometer. Copyright © 2016 John Wiley & Sons, Ltd.