Comprehensive Test Ban Treaty Research Articles

Investigation of Radioxenon Probability Density Functions at IMS Radionuclide Stations Using a Monte Carlo Method for Background Estimation

Abstract The International Monitoring System, the primary means of verification of the Comprehensive Nuclear-Test-Ban Treaty, monitors the planet for any sign of a nuclear explosion. Regarding the International Monitoring System radionuclide stations, it is known that radioxenon released from nuclear facilities such as medical isotope production facilities and nuclear power plants influences the stations. For the purposes of monitoring nuclear explosions, it is important to better understand the radioxenon background based on these nuclear facilities. The probability density functions of background activity concentration at IMS radionuclide stations are estimated using a Monte Carlo method based on emissions from known nuclear facilities and source receptor sensitivity data. This paper describes two case studies of radioxenon detections at radionuclide stations applying the developed approach. This method could be one of several prospective approaches to predict the activity concentrations of isotopes of radioxenon at radionuclide stations in Comprehensive Nuclear Test-Ban Treaty Organization’s (CTBTO’s) prototype xenon background estimation tool software. It can also be used in characterization of CTBT-relevant nuclear events for expert technical analysis. Plain Language Summary Civil nuclear power stations and medical isotope production facilities release radioisotopes of xenon during their normal operations. These emissions would make it harder to detect xenon produced from any nuclear weapon test that might occur. A method is described that starts with information about civil releases and produces a statistical description of the concentrations of isotopes measured at stations designed to detect nuclear tests. This information makes it possible to enhance nuclear explosion detection performance.

The entanglement of fusion energy research and bombs

ABSTRACT The recent achievement of fusion ignition—meaning more energy came out of a self-sustaining fusion reaction than was put in—at Lawrence Livermore National Laboratory’s National Ignition Facility has brought to the fore long-simmering questions about whether certain experiments violate the Comprehensive Test Ban Treaty on nuclear explosions. Fusion research for peaceful use and military use are highly intertwined, despite attempts to cloak nuclear weapons with the aura of the so-called “peaceful atom.” Ignition has been achieved, but there is still a remarkable silence around whether pure fusion weapons—weapons that could kill large numbers of humans with neutron radiation but have blast effects much smaller than current thermonuclear weapons—are an objective of the overall program. Even if not an explicit objective, would they be built if fusion technology makes them feasible?

Internal gravity waves in the middle atmosphere and their impact on infrasound propagation across the International Monitoring System

Infrasound technology is used to monitor atmospheric events in order to guarantee compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Over the 60 infrasound stations initially planned, 53 are operational to date as part of the International Monitoring System (IMS). As opposed to the waveform-related technologies that are used by the IMS to monitor the two other media of the geosphere (the underground and the oceans), infrasound waves are travelling in a continuously varying propagation medium. From minutes to hours and from a few hundreds of meters in the vertical to thousands of kilometers in the horizontal, atmospheric perturbations affect detection capabilities of the IMS at various scales. These perturbations need to be taken into account, for infrasound analysis to be able to provide accurate localization and characterization of sources of interest. In particular, internal gravity waves (atmospheric buoyancy waves) pose a serious challenge to atmospheric modelling because of the unresolved involved processes. They can dramatically affect transmission losses across the globe. Through numerical experiments and using high resolution modelling outputs of the atmosphere, backed up by atmospheric measurements, we demonstrate how gravity waves impact infrasound attenuation and drive signal amplification across the IMS.

Studying infrasound propagation in the middle atmosphere with ICON and UA-ICON: comparison with the IFS and ground-based remote sensing

Infrasound signals are used to monitor various anthropogenic and natural sources. In particular, infrasound is one of the four verification technologies used by the International Monitoring System (IMS) of the Comprehensive Test-Ban Treaty organisation (CTBTO). To determine accurate source locations and energies, an accurate model of wind and temperature up to the lower thermosphere is necessary, hence operational NWP products are of great importance for routine infrasound monitoring activities. However, many of these models focus on tropospheric conditions, and the middle atmosphere (MA) is not well represented. UA-ICON is an upper atmosphere version of the ICON model that provides modelled atmospheric parameters up to 150 km. First, to assess ICON and IFS operational analysis products, comparisons to lidar observations are made. The main differences between both products were analysed with respect to winds and temperatures in the MA. Second, UA-ICON simulations outputs were compared to ICON and IFS fields to demonstrate the increased wave activity above ~30 km with UA-ICON. The added value of UA-ICON with respect to ICON and IFS for infrasound propagation simulations is discussed. The comparisons between the instrumental observations and the models will be presented, as well as comparisons between modelled and measured infrasound propagation.

Computational Optimization of 133m Xe Production in the Washington State University TRIGA Reactor

Here we present a new method of irradiating 132Xe capsules with neutrons to produce 133mXe gas standards that are used for radiation detector calibration at radioxenon measurement laboratories in support of the Comprehensive Test Ban Treaty (CTBT). This method is designed to maximize the production of 133mXe compared to 133Xe, both of which are competing products from the 132Xe(n, g) reaction. The 133mXe is produced at a much higher fraction for high-energy neutron absorptions in 132Xe (~50% for fast neutrons versus ~11% for thermal neutrons). We performed “spectral tuning” of the Washington State University (WSU) TRIGA reactor neutron spectrum inside the 132Xe ampules to maximize the number of fast neutrons and minimize the number of thermal neutrons available for 132Xe absorption. Spectral tuning analysis, done with Monte Carlo simulations, provided valuable insights into a future final design for a 132Xe irradiation capsule. With no spectral tuning, the fractional yield of 133mXe in the WSU reactor was ~11.7%. By surrounding the 132Xe capsule with a 0.5-cm-thick layer of tungsten and a 2.83-cm layer of europium (III) oxide and placing it in the reactor’s cadmium rotator tube next to the fuel elements, the fractional yield of 133mXe can be increased to 24.6%, a 111% increase in yield. Thus, by improving the fractional yield of 133mXe through spectral tuning, the CTBT will have better quality gas standards to use for radioxenon detector calibration to assist in the CTBT’s mission.

Inferring the Focal Depths of Small Earthquakes in Southern California Using Physics-Based Waveform Features

ABSTRACT Determining the depths of small crustal earthquakes is challenging in many regions of the world, because most seismic networks are too sparse to resolve trade-offs between depth and origin time with conventional arrival-time methods. Precise and accurate depth estimation is important, because it can help seismologists discriminate between earthquakes and explosions, which is relevant to monitoring nuclear test ban treaties and producing earthquake catalogs that are uncontaminated by mining blasts. Here, we examine the depth sensitivity of several physics-based waveform features for ∼8000 earthquakes in southern California that have well-resolved depths from arrival-time inversion. We focus on small earthquakes (2<ML<4) recorded at local distances (<150 km), for which depth estimation is especially challenging. We find that differential magnitudes (Mw/ML–Mc) are positively correlated with focal depth, implying that coda wave excitation decreases with focal depth. We analyze a simple proxy for relative frequency content, Φ≡log10(M0)+3log10(fc), and find that source spectra are preferentially enriched in high frequencies, or “blue-shifted,” as focal depth increases. We also find that two spectral amplitude ratios Rg 0.5–2 Hz/Sg 0.5–8 Hz and Pg/Sg at 3–8 Hz decrease as focal depth increases. Using multilinear regression with these features as predictor variables, we develop models that can explain 11%–59% of the variance in depths within 10 subregions and 25% of the depth variance across southern California as a whole. We suggest that incorporating these features into a machine learning workflow could help resolve focal depths in regions that are poorly instrumented and lack large databases of well-located events. Some of the waveform features we evaluate in this study have previously been used as source discriminants, and our results imply that their effectiveness in discrimination is partially because explosions generally occur at shallower depths than earthquakes.

Stratospheric Gravity Waves Impact on Infrasound Transmission Losses Across the International Monitoring System

AbstractThe international monitoring system (IMS) has been put in place to monitor compliance with the comprehensive nuclear-test-ban treaty (CTBT). Its infrasound component, dedicated to the monitoring of atmospheric events, gives also room to civil applications (e.g. monitoring of volcanic eruptions, meteorites, severe weather). Infrasound detection capabilities are largely determined by the state of the middle atmosphere. This requires an accurate knowledge of the atmospheric processes at play. More particularly internal gravity waves (GW) pose a challenge to atmospheric modelling because of unresolved processes. Using high-resolution simulation outputs over winter 2020 (20 January–1 March) we present a method to assess the impact of GW on infrasound surface transmission losses across the IMS. We validate the method by comparing simulated GW perturbations to GW lidar observations at Observatoire de Haute-Provence in France, and satellite-based GW energy estimations globally. We perform propagation simulations using atmospheric specifications where GW are filtered out and kept in, respectively. We demonstrate that the largest impact of GW across the IMS is not where GW activity is the largest, but rather where GW activity combines with infrasound waveguides not firmly set in a given direction. In northern winter, the largest variations of transmission losses at 1 Hz due to GW occur in the southern (summer) hemisphere in the direction of the main guide (westward propagation), with average values ranging between 10 and 25 dB in the first shadow zone. It corresponds to an average signal amplification of at least a factor 5 to 15, while this amplification is around 2 to 5 for the main guide in the northern winter hemisphere (eastward propagation).

Seismic Discrimination Between Nuclear Explosions and Natural Earthquakes using Multi-Machine Learning Techniques

AbstractIn the field of seismic signal analysis, it is of utmost importance to accurately differentiate between earthquakes and underground nuclear explosions. As a contribution for the verification regime of the Comprehensive Nuclear Test Ban Treaty (CTBT), Various methods have been employed for this purpose, including Complexity, Spectral ratio, mb—Ms (body wave and surface wave magnitudes), and corner frequency of P and S waves. These discrimination techniques have been examined to manually identify natural seismic events from nuclear explosions across different regions worldwide, such as China, India, Pakistan, North Korea, and the United States. To gather the necessary data, a comprehensive dataset comprising nuclear explosions and earthquakes of the same magnitude range (4 ≤ mb ≤ 6.5) of 35 seismic events from 1945 to 2017 has been compiled from the International Research Institute for Seismology (IRIS) using broadband and long period seismic stations. The objective of this study is to employ a range of linear and nonlinear Machine Learning (ML) models with the aim of automatically distinguishing between underground nuclear explosions and large earthquakes to enhance the accuracy of manual feature extraction. For this purpose, time domain waveforms and different classifier techniques focused on feature extraction have been used. The ML models employed include logistic regression, K-nearest neighbours classifier, decision tree classifier, random forest classifier, voting classifier, and Naive Bayes. The outcomes of the ROC and AUC analyses were employed to validate the validity of our proposed discrimination algorithm. The results show that the Random Forest Classifier is the most effective model, obtaining 100% accuracy in the case of feature extraction, while the best model for the time domain waveform classifier that achieved 75.5% accuracy is the voting classifier.

India’s Chequered Relationship with the Comprehensive Test Ban Treaty: Examining Cross-Linked Concerns over Nuclear Disarmament and National Security

In 1994, India enthusiastically supported the United Nations process for negotiating the Comprehensive Test Ban Treaty (CTBT). It expected the treaty would ban all types of nuclear testing and pave the way for nuclear disarmament. The final treaty negotiated in 1996 did not commit itself to this goal of disarmament and India ultimately rejected it. However, behind this rejection also lies the story of India’s deteriorating national security outlook and decision-makers’ keen desire to avoid their country being subjected to a discriminatory nonproliferation regime enacted by the nuclear weapon states. The key questions guiding the query on (CTBT) are: What were the reasons behind India’s initial support of the CTBT in 1993? And what transpired between 1994 and 1996 that led India to change its stand?

Gamma-spectrometry measurements of filtration media from an Advanced Gas-cooled Reactor

Filtration media used to quantify particulate and gaseous releases have been collected from Hartlepool Power Station in the United Kingdom and measured using high-sensitivity gamma-spectrometry systems. Radionuclides that are relevant to the monitoring regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) have been detected. Results are reported and compared to detections recorded on the International Monitoring System (IMS). Time series activity plots have been produced and results interpreted with respect to known plant activities. The reported results improve the understanding of trace-level radionuclide emissions from Advanced Gas-cooled Reactors (AGRs) and aid interpretation of IMS measurements. This work is being performed as part of the Xenon Environmental Nuclide Analysis at Hartlepool (XENAH) collaboration between the Atomic Weapons Establishment (AWE, UK), EDF Energy (UK), Pacific Northwest National Laboratory (PNNL, US) and the Swedish Defence Agency (FOI, Sweden).

Relocation of 3 April 2017 Moiyabana Earthquake in Botswana Using Seismological Data from Local Network of Autonomously Recording Seismographs and International Monitoring System Stations

AbstractOn the 3rd April 2017 a widely felt Moiyabana earthquake shook Botswana and the rest of southern Africa. Previous Moiyabana earthquake locations used mainly teleseismic or regional seismograms; and/or non-seismic methods which include Synthetic Aperture Radar (InSAR), and magnetotelluric (MT). These results did not agree, as evidenced by the depth of the earthquake that ranged from zero to 30 km (i.e. indicating either a man-made event or a natural event); thus motivating us to re-assess the location parameters. Unfiltered seismic waveform data from the recent project of the Network of Autonomously Recording Seismographs (NARS) in Botswana was complimented with stations from the International Monitoring System (IMS) to relocate the event. Relocated parameters are origin time, epicentre, focal depth, and magnitude. Geotool software from the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), and the Regional Seismic Travel Time model (RSTT) were used to process vertical components waveforms from 9 NARS and 32 IMS stations. Geotool results are: earthquake epicentre (22.645 °S: 25.220 °E); origin time of 17:40:16.9 (UTC); hypocentral depth range of 22 to 24 km; body magnitude (mb) and local magnitude (ml) of 6.3 ± 0.6 and 6.0 ± 0.8, respectively. RSTT results are: earthquake epicentre (22.667 °S: 25.257 °E); origin time of 17:40:16.95 (UTC); hypocentral depth of 25 km; and mb of 6.65 ± 0.03. The seismological location parameters from Geotool and RSTT, agree very well within experimental uncertainties with the non-seismic geophysical methods.

The logic for US ratification of the Comprehensive Nuclear Test Ban Treaty

ABSTRACT The United States has accepted increasingly stringent limits on nuclear testing, culminating in the 1996 Comprehensive Nuclear Test Ban Treaty. However, the US Senate in 1999 failed to consent to ratification, given concerns about verifying the treaty and maintaining safe and reliable US nuclear weapons without testing. Since then, the US Stockpile Stewardship Program has matured and allowed certification that US nuclear weapons remain safe and reliable without nuclear explosive testing. Likewise, advances in the US Nuclear Detonation Detection System and the International Monitoring System make virtually all tests detectable. Bringing the Comprehensive Nuclear Test Ban Treaty into force is in the US interest, as it would lock in an American advantage in nuclear knowledge and expertise and hinder other states from developing more sophisticated nuclear arms. Unfortunately, however, American domestic politics and the difficult international environment make it unlikely that the treaty will enter into force in the near term.

New confidence-building measures can reduce tensions around subcritical tests

ABSTRACT With rising tensions between the United States on one side, and China and Russia on the other, the three countries have grown mutually accusatory about some testing activities they conduct to maintain and modernize their nuclear arsenals, with allegations made by the United States focusing on very low-yield fission experiments. In a world where trust in the nonproliferation regime is weakening and most bilateral arms control measures have been suspended, many experts fear that recriminations over very low-yield tests could spark a new escalation spiral to full-scale nuclear tests. Transparency measures could diffuse the suspicions around these tests and strengthen the Comprehensive Nuclear Test Ban Treaty, which is largely being complied with but still not legally in force.

Preserving the nuclear test ban after Russia revoked its CTBT ratification

ABSTRACT Russia’s withdrawal of its ratification of the Comprehensive Nuclear Test Ban Treaty in 2023 raised concerns about the possible end of the existing moratorium on nuclear explosions. But the moratorium continues to hold, largely thanks to the de facto norm against full-scale nuclear tests and the strength of institutional structures created by the treaty. Transparency of nuclear experiments demonstrated by the United States will be an important factor in upholding the moratorium, and Russia and China should be encouraged to be more transparent about their activities as well. Any disputes about the exact nature of their experiments and their adherence to the strict definition of a zero-yield nuclear explosion should not become reasons to question the value of the moratorium—or the ability of parties to verify and enforce the test ban once the treaty comes into force.

The use of in situ infrasound calibration to correct wave parameter estimation

As part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the International Monitoring System (IMS), which includes infrasound stations, has been established to monitor nuclear testing, as well as many other infrasound sources of interest to the scientific community. To minimize the effects of wind-noise, wind-noise reduction systems (WNRS) are installed as part of each sensor. In order to provide the best wave parameter (azimuth, trace velocity, amplitude) estimates, the response of the WNRS must be properly taken into account. Therefore, it is important to perform an in-situ calibration of the sensor using a co-located reference sensors and ambient signals to determine this response. This in-situ calibration can be used to monitor the status of the sensors, and provide feedback to the station operators. Experiments were performed at the IS26 site in Germany using a temporary WNRS to provide quantitative measurements of the effects of the WNRS and its calibration on the wave parameter estimation. These calibration results were used to provide corrections to the raw signal data for retrieval of the corrected wave parameters and were compared to the IS26 measurements, demonstrating that accurate measurements can be retrieved using the in-situ calibration.

Using sensors of opportunity to estimate the density of blue and fin whales

The “Combining global OBS and CTBTO recordings to estimate abundance and density of fin and blue whales”, or CORTADO project, is using data from two bottom-sensor types to implement a suite of methods for estimating density of fin and blue whales. While previous studies have demonstrated the utility of Ocean Bottom Seismometers (OBS) and Comprehensive Test Ban Treaty Organization (CTBTO) hydroacoustic data, the techniques have not yet been developed to the point where they can be routinely applied by the wider research community. The primary CORTADO goal is to provide a set of software tools and training materials to expand access and usability of large, historic datasets. This talk will focus on using the CTBTO sensors for estimating density with a bearing method. This technique uses the bearing of and the signal-to-noise ratio for each detected call to estimate how many animals are producing a set of calls at any given time over the detection range of the sensor at all bearings. Applying this tool to several CTBTO sensors, we can compare the amount of blue and fin whales over time as well as spatially across the northern and southern coverage areas of the sensor array.

A comparison of tidal components across multiple sites using ultra-low frequency ocean acoustic measurements

Recent long-term analysis of the hydrophone measurements taken in the deep sea reveals indications of multiple tidal components. Tidal harmonics corresponding to solar and lunar diurnal and semi-diurnal tide components were determined by analyzing the Cepstrum (variance of a spectral power) of the year or more long time series (0.5 Hz) of mid-water column measurements taken by the United Nations Comprehensive Test Ban Treaty Organization (CTBTO) in the Pacific, Atlantic and Indian Ocean. Postulations for the origin of this signal include rolling rocks, ocean turbulence, a change in the surface height, currents, mechanical/electrical (non-acoustic) noise and wind/wave induced noise propagating in the ocean. In this paper, this work is extended to more sites and encompasses a larger portion of the ultra-low frequency range (i < 5 Hz). it is found that different sites have quite different tidal components (as expected) but also have different frequency components (some with 0.5–1 Hz and others with 3–5 Hz). This opens the possibility of acoustic soundscape differences between sites due to regional source generation and local acoustic propagation.

Development and Operation of a Global‐Scale Seismographic Network: The IRIS/USGS GSN

AbstractFrom inception in the late 1980s up to the present, the Global Seismographic Network has produced high quality seismic data that has advanced research into the structure of the Earth's deep interior particularly the large‐scale heterogeneous elastic/anelastic structure of the mantle and core. The network's breadth of coverage enables images of great earthquakes impossible to obtain from regional networks or array data alone. Analysis of the data has provided new insights into non‐traditional seismic sources such as slow earthquakes, glaciers and landslides. Ancillary meteorological and infrasound sensors collocated at the sites support unique studies of volcanic events such as the recent eruption of the Hunga Tonga–Hunga Ha'apai volcano. Near real‐time transmission of the data to hazard warning centers has expanded the network's usefulness as a tool for rapid response to earthquakes, for warning communities effected by tsunamis, and for monitoring compliance with nuclear test ban treaties. The successful construction and operation of the network would not be possible without the outstanding international cooperation of many governmental, academic and private groups who have hosted components of the network.

Q&A Aftab Khan, a career in geophysics

Abstract Sue Bowler talks to Aftab Khan, who recently celebrated his 90th birthday, about his career in geophysics, from the origins of the modern subject, through the exploration of the African Rift Valley and the steps to a nuclear test ban treaty

Beyond The Nuclear Explosion Verification Monitoring, the Comprehensive Nuclear-Test-Ban Treaty Offers A Strong Capacity Building System Support

Purpose: The United Nations (UN) General Assembly, as part of nuclear non-proliferation and disarmament measures to prohibit nuclear test explosions and any other nuclear explosions in all environments (in the atmosphere, oceans, and underground) adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Thus, it ultimately enhances international peace and security. It is an essential step aimed at making the world a safer place. States that agree to sign on to this Treaty will be contributing to the protection of human health and the environment against nuclear test explosions and their severe impacts. This paper seeks to demonstrate that the CTBT beyond its global prohibition measure against all nuclear explosions, is offering a strong Capacity Building System support to State Signatories such as the Republic of Ghana. The CTBT global verification regime is built to monitor States Signatories compliance with the Treaty. CTBT Organization (O) through the International Data Centre (IDC) provides States Signatories with technical assistance to support their verification responsibilities to ensure effective global monitoring.
 Methodology: The Republic of Ghana through the Capacity Building project under the IDC technical assistance to States Signatories is a beneficiary of equipment support commissioned in July 2021. Under this project the GCI-III/VSAT equipment set was received from the IDC, establishing a new communication link for forwarding IMS waveform data from some selected stations in Africa in near-real-time to the National Data Centre – Ghana (NDC – GH). The IMS seismic data also contributes to prompt access to information on seismic events within our respective geographic territories globally, thus playing a complementary role.
 Findings: The monitoring data generated provides essential civil and scientific applications to greatly support to mitigate the effects of natural or man-made disasters. This is an example of what the CTBT is providing to Member States beyond the Treaty’s main purpose.
 Unique contributor to theory, policy and practice: It is therefore important for the international community to fashion out other multilateral agreements considering the possibility of incorporating the potential additional benefits States can derived from such agreements.