The Idaho National Laboratory (INL, USA), serves as a quality control laboratory for the Comprehensive Test Ban Treaty Organization. Unfortunately, INL lost its primary source of traceable 133Xe materials when the National Institute of Standards and Technology (NIST, USA) stopped producing this standard reference material. To address this gap, INL collaborated with the National Physical Laboratory (NPL, UK) in 2017 and 2018 through interlaboratory comparison experiments to validate INL’s 133Xe calibration. Following successful completion of these intercomparisons, two additional intercomparisons were performed in 2020 and 2021, incorporating a second radionuclide (131mXe) and three additional CTBTO affiliated analysis laboratories: Pacific Northwest National Laboratory (PNNL, USA), the Atomic Weapons Establishment (AWE, UK), and the Swedish Defense Research Agency (FOI, Sweden). Intercomparison results from all four exercises are presented and discussed.

Monitoring of the atmosphere for fission products (131mXe, 133mXe, 133Xe, and 135Xe) is performed by various laboratories to detect nuclear explosions. Quantification of 127Xe is not routinely performed by laboratories measuring atmospheric radioxenon because it is not a fission product. 127Xe was recently detected by a ground-based beta-gamma air monitoring system. When measured using beta-gamma coincidence detector systems, such as those in use on the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), 127Xe can interfere with the quantification of fission product radioxenon due to overlap of the 127Xe beta-gamma coincidence signatures with those of fission product radioxenon. This work demonstrates quantification of 127Xe at different laboratories with different measurement techniques. Production and purification of 127Xe was performed by neutron activation of enriched 126Xe. The purified 127Xe was then split between laboratories, and detection and quantification methods were developed. At Idaho National Laboratory, a quantification method involving high purity germanium detectors was devised that included self-attenuation correction. At AWE, a beta-gamma coincidence counting method, as used in support of the IMS, was modified to enable the measurement and analysis of the 127Xe samples. Corrections were made for self-attenuation, which showed a strong xenon volume dependency, for some coincidence signatures. The gas sample activity concentration was used as the comparison metric and it showed excellent agreement between the methods.

Underground nuclear explosions release noble gases into the atmosphere that can be detected to support international monitoring efforts. Atmospheric transport models help predict the movement of these gases over long distances, but struggle to predict the movement in the atmosphere local to the release. Afield experiment was designed to monitor the movement of 127Xe within a 5-km radius. Four gas samplers were deployed as part of this experiment to collect atmospheric samples at various distances from the release point. These samples were then analyzed in a near-field lab using a NaI(Tl) detector and in an off-site lab using gamma-gamma coincidence and beta-gamma coincidence counting.

A suite of measurement systems were deployed as part of the Physical Experiment 1 series of experiments, which involved detonating chemical explosives along with radionuclide tracers in an underground cavity, at the Nevada National Security Site (NNSS) in the United States. One of the radionuclide tracers, 127Xe was released from the containment following the explosion and detected on a SAUNA QB sampler situated approximately 3.5 km away. The system uses a beta-gamma coincidence detector system to measure fission product radioisotopes of xenon relevant to nuclear explosion monitoring. In this work we use the coincidence measurement data to analyse and interpret the results from the SAUNA QB system, to calculate the measured 127Xe activity concentration(s).

We describe a series of multi-physics experiments, referred to as Physics Experiment 1 (PE1) underway at the United States' Nevada National Security Site (NNSS). PE1 was designed to address fundamental science questions related to explosion monitoring, identifying distinct signatures of chemical explosions and differences between coupled and decoupled explosions. In addition, we seek to understand how multimodal observables vary with data type, distance, and other parameters and how data fusion across these observables may improve determination of source type and emplacement conditions. Each detonation includes tracers, a network of sensors to record seismic, acoustic, and electromagnetic waves, measurement of atmospheric conditions, and air sample collection for measurement of tracer concentration. Additionally, there are related experiments, focused upon individual modalities that employ well-characterized sources. Most recently, the fully coupled detonation experiment, PE1-A was conducted and excellent data return was achieved. We provide an overview of observations from PE1-A and results from some initial analyses. Some of our observations confirm prior expectations, while others provide surprising lessons learned from the multimodal data acquired. The results highlight the importance of performing large field experiments at scale that include interdisciplinary teams addressing the impact of multiple modalities. The project includes a sophisticated data management plan, and the PE1-A data will be released to the public in 2026.

The Xcounts algorithm for calculating air concentrations of radioactive xenon isotopes (Eslinger et al., 2023) has been extended to estimate 127Xe in addition to 131mXe, 133mXe, 133Xe, and 135Xe. The algorithm was applied to 119 samples collected with a SAUNA QB system (Ringbom et al., 2023) during a two-month atmospheric tracer release experiment. The algorithm identified two samples with 127Xe present from a single 1.5 h release about 3.5 km upwind of the sampler and no false detections of 127Xe were observed in the other samples.

Particulate mass estimation from 3-pixel images is desirable in many fields. Red–green–blue (RGB) analysis and Boolean logic were shown to estimate the mass of luminescent tracers in microscopic images. With a controlled background intensity, an estimation error of 1.8 to 3.5

In the early years of nuclear explosion monitoring, experts used downwind detections with meaningful ratios of radioactive species to identify an explosion. Today’s reality is sparse networks of radionuclide monitoring stations looking for weak signals. Analysts need to discriminate between industrial background radioactivity and nuclear explosion signals, even using the detection of one isotope. Aerosol and xenon measurements potentially related to nuclear tests in 2006 and 2013 announced by the Democratic People’s Republic of Korea and from worldwide civilian background radioactivity are considered when defining radionuclide detection anomalies to objectively guide the use of limited analyst resources and reduce the possibility of not detecting nuclear explosions.

To explore particulate movement near the plasma of chemical explosions, rugged tracer particles were placed within and on the exterior of metal charges and electrically detonated. The particles were collected on/in the porous walls of plastic cylinders at diameters that correlated to the plasma width during different phases of the explosion. The particles’ positions were determined by Boolean logic analysis of their luminescent intensity. The cylinders which caught particles from the initial phases of the explosion retained placement information, while wider cylinders showed uniform mixing. These results/analysis methodology can help improve the understanding of particulate mixing in harsh environments. Graphical abstract

Tracking mass through harsh environments requires surrogate particles that withstand the event and endure until sampling. Silica-covered quantum dots have been shown to withstand a range of environmental pHs from months to years; in this work they are shown to endure in anticipated local environments. Two methods of particle synthesis were employed to produce luminescent silica with particle diameters 0.1–4 μm. These tracer particles scale for mass production, tolerate harsh environments, and endure in debris. They could be deployed in places such as chemical explosions, industrial processes, geologic test beds, oil and gas fields, nuclear reactors, and geothermal plants to track mass under harsh conditions. Graphical abstract

The International Monitoring System includes a network of radionuclide detector stations and laboratories operated around the world monitoring for nuclear explosions. The United States Radionuclide Laboratory for radioxenon detection (USL16-NGL) was certified by the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization in 2016. Since the certification of the laboratory, an additional set of four radioxenon detectors have been added to the laboratory. These supplementary radioxenon detectors allow for improved throughput for the laboratory and improving the ability to measure short lived radioxenon isotopes. In this paper, we describe the implementation of the additional radioxenon detectors and how they compare to current capabilities. Additionally, we detail implementation procedures to leverage the increased throughput.

The International Monitoring System includes a network of radionuclide detectors operated around the world monitoring for nuclear explosions. A key aspect of the International Monitoring System is the detection of radioxenon with a network of stations and laboratories. Beta-gamma detectors are utilized extensively for the detection of radioxenon, and the beta detection is primarily performed with a plastic scintillator cell. Two areas of improvement for plastic scintillator are the sample carry-over (“memory effect”) and energy resolution. While the scintillator can be coated to remove the memory effect, the energy resolution must be improved with a different detector material. Silicon is the current leading candidate for the future beta cell material due to the much-improved energy resolution compared to plastic scintillators (factor of ~ 3x). PNNL is developing a silicon beta cell for use as a potential modular replacement within Xenon International (a next generation radioxenon detection system currently undergoing acceptance testing for potential inclusion in the International Monitoring System). The beta cell utilizes four different silicon detectors to create an active volume for the radioxenon within an outer gas cell. Since there are four separate beta signals (compared to one for plastic scintillators), data acquisition modifications are required. In this paper, we detail the design, efficiency measurements, and long-term testing of the silicon beta cell and potential improvements in isotopic discrimination.

Explosives are often used in industry, geology, mining, and other applications, but it is not always clear what remains after a detonation or the fate and transport of any residual material. The goal of this study was to determine to what extent intact molecules of high explosive (HE) compounds are detectable and quantifiable from post-detonation dust and particulates in a field experiment with varied topography. We focused on HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane), which is less studied in field detonation literature, as the primary explosive material and RDX (1,3,5-Trinitroperhydro-1,3,5-triazine) as the secondary material. The experiment was conducted at Site 300, Lawrence Livermore National Laboratory's Experimental Test Site, in California, USA. Two 20.4 kg and one 40.8 kg above ground explosions (primarily comprised of LX-14, an HMX-based polymer-bonded high explosive) were detonated on an open-air firing area on separate days. The complex terrain of the firing area (e.g., buildings, berm, low-height obstacles) was advantageous to study HE deposition in relation to plume dynamics. Three types of samples were collected up to 100 m away from each shot: surface swipes of aluminum plates, surface swipes of fixed objects, and filters from air samples. We used atmospheric flow tube-mass spectrometry (AFT-MS) to quantify picogram levels of molecular residue of HE material in the post-detonation dust. An aliquot of sample extract in methanol (e.g., 1 mu L of 0.5 mL) was placed onto a resistive material and then thermally desorbed into the AFT-MS. We successfully detected and quantified both HMX and RDX in many of the samples. Based on mass (pg) detected and solution dilution, we back-calculated the mass collected on the swipe or filter (ng per sample). The aerial distribution of molecular residue was consistent with the path of the plume, which was strongly determined by wind speed and direction at the time of each shot. The quantity of material detected appeared to correlate more with distance from the shot and the wind conditions than with shot size. This study demonstrates that the picogram detection levels of AFT-MS are well-suited for quantification of analytes (e.g., HMX and RDX) in environmental samples.

For decades, physicists have used neutrinos from nuclear reactors to advance basic science. These pursuits have inspired many ideas for application of neutrino detectors in nuclear energy and security. While developments in neutrino detectors are now making some of these ideas technically feasible, their value in the context of real needs and constraints has been unclear. This report seeks to help focus the picture of where neutrino technology may find practical roles in nuclear energy and security. This report is the final product of the Nu Tools study, commissioned in 2019 by the DOE National Nuclear Security Administration (NNSA) Office of Defense Nuclear Nonproliferation Research and Development (DNN R&D). The study was conducted over two years by a group of neutrino physicists and nuclear engineers. A central theme of the study and this report is that useful application of neutrinos will depend not only on advancing physics and technology but also on understanding the needs and constraints of potential end-users. The Study Approach emphasized broad end-user engagement. The major effort, undertaken from May to December 2020, was a series of engagements with the wider nuclear energy and security communities. Interviews with 41 experts revealed points of common understanding, which this report captures in three Cross-Cutting Findings, a Framework for Evaluating Utility, and seven Use Case Findings. The report concludes with two Recommendations. The findings and recommendations are summarized below. The respective ordering within each category does not represent a prioritization or implied value judgement.

Fission explosions produce large numbers of antineutrinos. It is occasionally asked whether this distinctive, unshieldable emission could help reveal clandestine nuclear weapon explosions. The practical challenge encountered is that detectors large enough for this application are cost prohibitive, likely on the multi-billion-dollar scale. In this paper, we review several hypothetical use cases for antineutrino detectors as supplements to the seismic, infrasound, hydroacoustic, and airborne radionuclide sensors of the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System. In each case, if an anti-neutrino detector could be constructed that would compete with existing capabilities, we conclude that the cost would considerably outstrip the value it might add to the existing monitoring network, compared to the significantly lower costs for the same or superior capability.

The International Monitoring System includes a network of radionuclide detectors operated around the world monitoring for nuclear explosions. A key aspect of the International Monitoring System is the verification of the results from the stations. The verification comes through calibration of the systems, and additional validation measurements from certified laboratories. In support of the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization, there are 16 radionuclide laboratories around the world (with a subset of those laboratories having radioxenon measurement capabilities). We have developed a laboratory system for processing and measuring the radioxenon archive samples from the International Monitoring System. In this paper we describe the design and operation of the laboratory in support of verification of the Comprehensive Nuclear-Test-Ban Treaty.