Strengthening Nuclear Security with ML: Full-Spectrum 137Cs Burial Depth Estimation

The physical processes governing advective and diffusive gas movement and distribution in dry soils are, in general, well understood and quantified. In this study, we derived and applied analytical and numerical models to describe these processes under different conditions and scenarios and conducted gas flow experiments in 200‐L barrels packed with dry quartz sand in a temperature‐controlled laboratory. We used either pure N 2 (0% O 2 ) or atmospheric air (20.9% O 2 ) injection or gas extraction from (or into) buried point sources (or sinks) to examine the effects of (a) source depth, (b) source discharge rate, and (c) injection cycle period on gas concentration and pressure distribution. We further quantified the contribution of diffusion from the atmospheric soil surface for the different scenarios, made possible by injecting N 2 and tracking the complementary O 2 concentration [i.e. the difference between atmospheric (20.9%) and the measured soil O 2 concentration]. An analytical solution for steady air flow from a point source in a finite, cylindrical domain is presented. The main findings are that air injection, and air extraction, are efficient at aerating the soil volume above the buried gas source or sink. On the other hand, air injection increases the aeration's effectiveness, especially below the source. Shortening the cycle period of gas injection increases gas‐use efficiency (i.e., increases the injected gas concentration) in most of the soil domain. The measurements were in good agreement with the results computed by the models’ analytical and numerical solutions.

Ground deformation and blast wave propagation in dry sand subjected to buried explosion: A centrifuge modelling study

A method of range and depth estimation was studied using a single hydrophone based on the dispersive characteristic and time-frequency analysis for low frequency underwater acoustic pulse signals in shallow water environment. First, the signal received on a single hydrophone can be decomposed into a series of modes within the frame work of normal mode theory, and then the dispersive characteristic of the propagating modes can be analyzed using the time-frequency analysis. In order to improve the time-frequency resolution, the use of the time-frequency distribution with adaptive radial-Gaussian kernel extracts the arrival time difference of propagating modes in dispersion curve, which can be used to estimate source range. Mode energy can be extracted using binary time-frequency mask filtering based on multi-mode joint matching processing; and the source depth can be estimated by comparing the differences of the mode energy of the real data and simulated replica data, yielding a contrast function. Simulation results from a shallow-water Pekeris waveguide show that the time-frequency distribution with adaptive radial-Gaussian kernel represents well the dispersion characteristics of the underwater acoustic pulse signals, provides higher time-frequency resolution and overcomes the problem of the inherent limit for the time resolution and frequency resolution in the traditional short-time Fourier transform, so that the modes can be separated and identified more easily in the time-frequency plane. From the result of the range estimation, the different mode combinations have different results of the range estimation. The range estimation result can be obtained accurately by using the mode with high energy in the time-frequency plane. The relative error in range estimation is less than 2% by using the mode with high energy. In terms of the depth estimation, the more the number of joint matching mode, the more sharp peak and low fake peaks the contrast function has, so that the depth estimation is further improved by incorporating more modes. This research has great significance for studying the extraction and separation of low frequency underwater acoustic pulse signals.

The concept of assessing safety culture in an organization emerged with its application at the nuclear power industry and has expanded since then. An assessment of nuclear security, on the contrary, is still under-developed, especially at non-nuclear facilities, such as academic institutions and medical facilities. To identify the level of the awareness and understanding of credible nuclear and radiological threats, response preparedness, security culture, and the integrity of nuclear security systems among non-radioactive material users at a university setting; a campus-wide survey was deployed. A total of 3,336 non-radioactive material users, including students, faculty, and staff participated in the survey. The survey was divided into three categories: general awareness (GA), school specific awareness (SSA), and behavior response (BR) awareness. Because the overall population of a university is rarely homogenous, six demographic characteristic groups of age, gender, work-status, degree, ethnicity, and nationality were added to the survey to identify the disparities in the attitudes that exist within the group of non-radioactive material users and the survey response. The results indicated significant association of the demographic groups of gender, age, work-status, degree, and ethnicity with the mean response scores across the three survey categories. An ordinal logistic regression was performed to identify and predict the impact of the demographic characteristics on the survey response. Findings from this study predicted the work status demographic group of undergraduates and graduates (younger age sub-groups) to possess higher level of general and behavioral response awareness than the remaining relatively higher work status sub-groups and the corresponding older age demographic sub-groups. The results from the school specific awareness category demonstrated contradictory outcome than the GA and BR survey categories. The results of this investigation are valuable as it provides a provisional understanding of the disparities in perception on the degree of nuclear and radiological security awareness across a group of diverse socio-demographic characteristics.

Since the bottom vertical short array deployed in the deep sea has the advantage of strong concealment, this paper proposes a matched beam intensity processing method adapted to the bottom vertical array for the estimation of the depth of the deep sea source, derives the relationship between vertical array beamforming and source range and depth based on the principle of Lloyd mirror interference, and reveals the tracking beam space fluctuation caused by source depth modulation. This paper proposes a deep-sea source depth estimation method based on beam intensity matched. The source depth estimation is realized by matched tracking beam fluctuation of data and tracking beam fluctuation of copy field. Based on simulation data, the effectiveness of the method of using vertical array data to match beam intensity to estimate the source depth is verified, and the depth estimation algorithm is verified based on the sea trial data of a deep sea area.

The wideband source localization is analysed widely in shallow water. It is pointed out that its performance is poor when the number of array elements is few or the ocean environment is uncertain. A method of estimating the range and depth is studied by using a single hydrophone based on the relationship of the horizontal wavenumber difference between two modes with the waveguide invariant for low frequency underwater acoustic pulse signals in a range-independent shallow water waveguide. This localization method estimates the source range by using the rangedispersion two-dimensional（2D) plane focus phenomenon and also the source depth by matching the modal energy. So it can separately estimate the source range and source depth by single hydrophone. First, the signal received on a single hydrophone can be decomposed into a series of modes within the framework of normal mode theory. In order to obtain a better localization performance, the first few order modal dispersion parameters and waveguide invariant are regarded as the unknown parameters. And then the first few order modal dispersion parameters and waveguide invariant can be estimated by comparing the differences between the modal phase velocity calculated by Eq.(8) and that calculated by the Kraken model. Second, using the estimated dispersion parameters and waveguide invariant for dedispersion transform, the amplitudes of each normal mode can achieve maximum values but only when the range of the received signal after dedispersion transform is equal to the range of source. On range-dispersion 2D plane, there appears the sound pressure focus phenomenon, and this phenomenon can be used to estimate the source range. Simulation results from a shallow water Pekeris waveguide show that the time-frequency distribution represents well the dispersion characteristics of the underwater acoustic pulse signal and the dedisperision transform can eliminate this dispersion at the range of source, so that the source range can be estimated. Besides, the first few order modal signals received are clearly separated in time domain after dedispersion transform, and the first few order modal energy can be calculated accurately. So the source depth can be estimated by matching the modal energy. The errors in range estimation and depth estimation are little in simulation. Finally, the data collected from airgun sources during an experiment in the shallow water are used to verify the presented method, and the experimental results obtained using airgun sources on a straight line are shown. The presented method is very significant for estimating the range and depth in shallow water.

The polarization of the acoustic field in the ocean waveguide environment is a unique property that can be measured by using a particle velocity sensor in the water column. It can provide new ideas for locating and detecting the underwater target, so it is interesting to study the polarization. The polarization of a monochromatic signal has been described by the Stokes parameters, a set of four real-valued quantities in previous work. In this work, the Stokes parameters are extended to the broadband form, and the expression is simplified by using the nonstationary phase approximation, which reduces the complexity of the theoretical derivation and reveals the physical mechanism behind the significant variations in polarization with source depth and symmetrical depth. Theoretical analysis shows that the polarization characteristics in the ideal waveguide vary significantly in the sea surface, the sea bottom, the depth of the sound source and symmetrical depth. In this work the numerical simulation is used to verify the theoretical analysis and study the relationship between range and integral bandwidth when nonstationary phase approximation method is effective. The numerical results demonstrate that the simplified expression using the nonstationary phase approximation is effective and can better characterize the depth distribution characteristics of the polarization. Additionally, by normalizing the broadband Stokes parameters, the effect of range on the depth distribution characteristics of polarization can be removed. It means that the normalized broadband Stokes parameters are in theory free of the range and depend on the environment, the receiver depth and the source depth, which have the potential to be used for source depth estimation. Subsequently, focusing on normalized broadband Stokes parameters, we analyzes the effects of parameters such as source frequency, source depth, sound speed profile and water depth on the depth distribution characteristics of polarization. The analysis results show that environmental factors have great influence on the depth distribution characteristics of polarization. In the end, the validity of the nonstationary phase approximation and the range-independent property of the normalized broadband Stokes parameters are verified by the results of the RHUM-RUM experimental data processing. The findings provide a theoretical basis for passive target depth estimation based on polarization.

—Power spectra analysis of aeromagnetic data from the southeast North Sea, where the depth to the top of the magnetic sources is reasonably well constrained, indicates that the scaling factor or spectral exponent (β) in an area with thick sediment cover is likely to be significantly different from the expected value of -3. This is consistent with the results from analyzing the KTB susceptibility data, which show that the magnetic scaling factor changes with burial depth. For sources shallower than about 1 km, a β value of -2.3 is roughly consistent with previous similar investigations. For sources deeper than a few kilometers, the β value could be as low as -1.0. Therefore, the depth estimation using power spectra analysis of magnetic data should be treated with caution, especially if there is no independent constraint on the source depth or the scaling factor (for instance from susceptibility logs in boreholes).

Reviewed by: Learning from a Disaster: Improving Nuclear Safety and Security after Fukushima ed. by Edward D. Blandford, Scott D. Sagan Takuji Okamoto (bio) Learning from a Disaster: Improving Nuclear Safety and Security after Fukushima. Edited by Edward D. Blandford and Scott D. Sagan. Palo Alto: Stanford University Press, 2016. Pp. 232. $27.95. Except one environmental historian, the contributors to this collection of articles are social scientists and engineers, and all chapters, including the one by the only historian, mainly analyze contemporary factors that caused and probably worsened the disaster in the Fukushima Daiichi nuclear plant in March 2011. Historians, nevertheless, will find the topics discussed here relevant to their interests. Those who regard the unprecedented tsunami as the cause of the Fukushima nuclear failure might think that it could not have been prevented anyway. They might even accept the inadequate seawall heights of the nuclear plant as the result of reasonable statistical risk analysis concerning the historical tsunamis. However, after seeing Nobumasa Akiyama (Chapter 4) argue that poor crisis leadership in the government and the power company [End Page 192] prevented appropriate decision-making right after the earthquake and tsunami, one might start wondering whether the disaster could not have been handled in a somewhat better manner, though stopping it from developing at all might seem inconceivable. It might not have been so bad as it actually was. Toshihiro Higuchi (Chapter 5) criticizes the Tokyo government’s over-reliance on numerical standards for radiation protection that confused and troubled the evacuating population. Both Kaoru Naito (Chapter 3) and Kazuto Suzuki (Chapter 6) point to the possible effectiveness of the synergy between nuclear security and safety efforts, represented by the so-called B.5.b measures developed after 9/11 in the United States, which were somehow not adopted by the Japanese. Phillip Y. Lipsy, Kenji E. Kushida, and Trevor Incerti (Chapter 7) conclude that in Japan, the largest power companies’ nuclear plants were more vulnerable to tsunami and flooding than those of the smaller businesses, implicitly blaming the power industry’s regional monopoly system. Furthermore, Edward D. Blandford and Michael M. May (Chapter 8) summarize that in addition to being part of the background of the failure, “lack of transparency before the accident made the political consequences of the accident more severe than they might otherwise had been” (p. 195). And finally, according to Gregory D. Wyss (Chapter 2), even the siting and design of the Fukushima Daiichi and its inadequate seawall heights were the results of the Design Basis philosophy that the Japanese government and nuclear industry had been invoking. With a different Design Basis philosophy, the flooding could have been prevented on 11 March 2011, as was observed at the Onagawa plant, which underwent a tsunami as high as the one that struck Fukushima Daiichi (Kushida, Chapter 1). After these examinations of the factors that caused and worsened the disaster, the authors naturally look to the future and suggest ways to improve worldwide nuclear safety and security. The social scientists’ and engineers’ analyses of the Fukushima disaster will give historians precious insight on where they should seek its historical root causes. Besides topics that have been discussed well since the Fukushima nuclear failure, some other issues still remain untouched. They include, for example, apparent disregard of security matters in the nuclear industry, lack of concern with crisis management in the government, and historical development of the use of Design Basis. Though these may no longer seem to be closely related to the interests in the Fukushima disaster, they can open up new possibilities for historical study of technology in general, which would not have been very obvious to historians but for such contemporary analyses as this book presents. [End Page 193] Takuji Okamoto Takuji Okamoto is professor of history of science at the University of Tokyo. His interest is in the history of physics in the United States, the development of operationalism of P. W. Bridgman, and the cultural and political implications of science and technology in modern Japan. Copyright © 2018 Society for the History of Technology

Summary We present a new method for interpretation of potentialfield anomaly data. A linear equation, involving the anomaly and its horizontal gradient, is derived to provide both the depth and nature of the buried sources. The proposed method is similar to the Euler technique; however, it uses a shape factor (q) instead of a structural index (η) to characterize the buried sources. The method is tested using theoretical simulations with different gravity and magnetic models placed at different depths with respect to the observation height. In all cases, the method adequately estimated the locations and the approximate shapes of the sources. Results from field examples will be discussed at the meeting.

The study of surface and shallow sources has lately become of importance, especially in connection with nuclear-explosion seismology (Ben-Menahem & Vered 1975; Ben-Menahem 1975). An ad-hoc study of surface sources was deemed necessary in view of the observation that, in general, the radiation pattern of a surface source differs substantially from the radiation pattern of the same source buried in an infinite space (White 1960). Consequently, an exact generalized multipolar ray theory (GMRT) is developed for surface sources. This theory holds but approximately for buried sources. However, for shallow sources the approximation is quite acceptable, while making the tedious evaluation of surface reflections redundant. The same problem of computing theoretical seismograms for shallow sources was recently investigated, in an approximate way, by Langston & Helmberger (1975). Radiation patterns of surface sources may be derived in different ways: ab initio solution of a surface source problem (e.g. Miller & Pursey 1954; Cherry 1962) or finding the radiation field of a buried source and taking the limit as the burial depth tends to zero (e.g. Pekeris 1955). We use a version of the second technique. The direct and reflected displacement fields for buried multipolar sources were given in detail by Ben-Menahem & Vered (1973). We form the total field by adding the direct and reflected fields. The resultant expression may be expanded in a Taylor series in a non-dimensional quantity which eventually may be shown to be kh where k is the wave number and h the burial depth of the source. Asymptotic ray expressions may be obtained by approximately evaluating the exact field entities using the stationary phase method and the initial motion approximation. The two main advantages of our method are that: (1) it applies equally easily to all multipolar sources, thus avoiding the need to re-evaluate the radiation pattern anew for every source, and (2) it may be straightforwardly applied to multilayered media. The first term in the above mentioned expansion yields the radiation pattern for surface sources. The second term in the series may be considered as a correction to be added to the first term, for small non-vanishing h, and so on. In this note we give (Table 1) the results for h = 0 only, which apply either exactly to surface sources or approximately to shallow sources such that the wavelength

The U.S. Geologic Survey National Earthquake Information Center (NEIC) monitors global seismicity, producing a catalog of earthquake source parameter information in near-real time that are used in earthquake hazard assessment and emergency response applications. The NEIC commonly relies on teleseismic observations to constrain earthquake source parameters (e.g., location, depth, magnitude, and mechanism) due to a lack of local and regional observations. For these teleseismically observed events, depth phase (i.e., pP, sP) arrival-time observations provide the best estimate on source depth. However, depth phases are often difficult to accurately identify and/or pick. Therefore, NEIC also uses waveform modeling, such as W-phase (Mww), body-wave (Mwb), and regional (Mwr) moment tensor estimations, to provide constraints on source depth. Although depth estimates from these approaches are informative, higher frequency observations provide more precise estimates because depth phases are more prominently observed at higher frequencies. Here, we present NEIC’s high-frequency (∼0.04 to 1 Hz) teleseismic waveform modeling approach, termed synthetic depth phase modeling (SynDepth), for determining source depth. SynDepth was developed to provide NEIC with a robust modeling procedure that provides rapid, accurate, and quantifiable estimates of earthquake source depth, when locator depths are indeterminant. This simple and fast procedure searches over 1-km-incremented source depths and an expanding triangular source time function to find the best-fitting solution. We compare automatic SynDepth solutions for a dataset of ∼1900 earthquakes (M 5.5–7.8) between 2015 and 2025 to NEIC-derived depth estimates from other methods and catalogs. We show this approach can provide a robust depth estimate for earthquakes lacking local arrival-time data, and it minimizes the need for review of depth-phase picks (pP, sP) or using predefined “fixed” depths.

In seismic nuclear monitoring, an accurate source depth is an important prerequisite for reliably estimating the explosive yield. Relative location methods are often used for this purpose. However, the conventional method based on regional Pn waves usually fails to give satisfactory constraints on the source depth, mainly due to the strong trade‐off between the burial depth and origin time. This study explores a high‐precision relative location method to simultaneously determine the relative epicenter and source elevation by using differential traveltimes from both downward‐takeoff Pn waves and horizontal‐takeoff Pg waves. The properties of both Pg and Pn waves, including the consistency between waveforms, the reliability of differential traveltime measurements, and their sensitivities to epicenter and depth variations, are investigated. By jointly applying both types of waveform data, the proposed method significantly enhances the constraint on the source depth variation. This method is applied to regional seismic data collected from China, South Korea, and Japan to determine the relative epicenters, origin times and relative burial depths of six North Korean underground nuclear explosions. The source depths are then used to provide burial‐depth corrections to estimate the explosive yields. The depths of the six North Korean nuclear explosions detonated on October 2006, May 2009, February 2013, January 2016, September 2016, and September 2017 are determined to be 330, 540, 506, 468, 521, and 570 m, respectively, and their yields after burial depth corrections are 1.6, 5.7, 13.4, 12.6, 21.7, and 225.7 kt, respectively.

We present an inexpensive imaging system for measuring the diffuse surface radiance profile produced by a light source within a turbid medium. The diffusion model of light propagation in multiple scattering media is used to estimate the optical properties of a sample and subsequently approximate the depth of an optical source. The system is shown to accurately estimate the relative changes in source depth in a homogeneous phantom. The absolute depth estimate may be improved with a better estimate of the optical parameters. Preliminary tests on a porcine skin sample show that the simple model can be used to roughly track the relative changes in the depth of a source in a layered medium. However, a rigorous model of the layered geometry may be required to more accurately localize a source, particularly near interfaces between tissue layers.

We estimate yields and source depths for the six North Korean underground nuclear explosions (UNEs) in 2006, 2009, 2013, 2016 (January and September), and 2017, based on regional seismic observations in South Korea. Spectral ratios of event pairs are calculated using seismograms from the six UNEs observed along the same propagation paths and at the same receivers. These relative seismic source scaling spectra for Pn provide a basis for a grid search source solution that estimates source yields and depths for each event pair based on assumed explosion source models by Mueller and Murphy (1971; MM71), Denny and Johnson (1991; DJ91), and Walter and Ford (2018; WF18). The grid search is used to identify the best fit to the empirical spectral ratios subject to the source models by minimizing the root mean square misfit in the frequency range of 0.2–15 Hz. To address the trade-off between depth and yield, a modified grid search was implemented that includes elastic propagation effects for different source depths using reflectivity Green’s functions, thus modeling slight differences in propagation path based on source depth. This addition reduces trade-offs between depth and yield, and results in better model fits to frequencies as high as 15 Hz compared with cases in which depth effects were not included. The modified grid search results indicate that both MM71 and WF18 models provide comparable source depth and yield estimates with good agreement between theoretical and observed spectral ratios matching both the long-period levels and the corner frequencies, whereas the DJ91 model estimates produce lower yields due to a difference in corner frequency scaling. The best grid search solutions produce yields from ∼0.9 kt for the first UNE and up to ∼290 kt for the explosion in 2017, with depths varying from ∼280 to ∼750 m.