Radionuclide Sensors Research Articles

Design of microfluidic radionuclide sensors: Combining microscale 3D printing based on 2-photon polymerization with nanoscale polymer brush scintillators

Development of miniature sensors for radionuclides is a challenging goal. In this paper we have applied specially developed vinyl-functionalized organic fluorophores for fabrication of nanoscale polymer brush scintillator coatings on artificially created 3D mesoporous structures. The applied 3D printing based on 2-photon polymerization is a modern approach, which extends the concept of additive manufacturing to the micro/nano-scale. One of the fundamental limitations of the 3D printing based on 2-photon polymerization (2PP) is a limited range of suitable photo-resins and, thus, limited functionalities of the resulting structures. To address this challenge, various post-processing technological steps, such as overcoating with conformal oxide layers and/or pyrolysis have been suggested. In this study, we demonstrate how chemical modification of 3D printed polymer structures with nanoscale polymer brush scintillators can be applied as a viable technological strategy for microfluidic radionuclide sensors. Application of new polymerizable organic fluorophores allowed “grafting to” or “grafting from” modifications of the photoresist surface with high concentration and precisely controlled location of the active scintillating units within the coating.

Antineutrino Detectors Remain Impractical for Nuclear Explosion Monitoring

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 European Arctic: A Laboratory for Seismoacoustic Studies

The International Monitoring System (IMS) for verifying compliance with the Comprehensive Nuclear‐Test‐Ban Treaty (CTBT) comprises sensors associated with four monitoring technologies: seismic, infrasound, hydroacoustic, and radionuclide. The so‐called waveform technologies (seismic, infrasound, and hydroacoustic) are used to detect and locate events that could constitute treaty violations. All four technologies may be employed to investigate the nature of events, with the network of radionuclide sensors in place to provide evidence of a nuclear explosion. Historical, political, and technical issues surrounding the CTBT are discussed by Dahlman et al. (2009, 2011). The global IMS infrasound network (Fig. 1) is primarily to detect signals generated by atmospheric nuclear tests. Figure 1. Status of the International Monitoring System infrasound network in August 2014. Filled symbols are certified stations sending data to the International Data Center (IDC) in Vienna. White symbols indicate the treaty coordinates of stations planned or under construction. The IMS infrasound network has been deployed over the last two decades (Brachet et al. , 2010; Christie and Campus, 2010), and only with the network approaching completion has a realistic picture of its detection capability emerged (Le Pichon et al. , 2009; Green and Bowers, 2010). The detectability of atmospheric signals is governed by a seasonally varying wind‐determined anisotropy. In the northern summer, the stratospheric winds blow predominantly east to west, facilitating the detection of infrasound at stations west of sources and inhibiting the detection at stations east of sources. In the northern winter, the winds blow in the opposite direction changing the sense of high and low detectability. The reverse patterns occur in the southern hemisphere. There is increasing interest in using infrasound for probing atmospheric structure (e.g., Lalande et al. , 2012), and the broader properties and applications of infrasound are discussed by Evers and Haak (2009) and Hedlin et al. (2012). In October …

Sources of Error and the Statistical Formulation of M S: m b Seismic Event Screening Analysis

The Comprehensive Nuclear-Test-Ban Treaty (CTBT), a global ban on nuclear explosions, is currently in a ratification phase. Under the CTBT, an International Monitoring System (IMS) of seismic, hydroacoustic, infrasonic and radionuclide sensors is operational, and the data from the IMS is analysed by the International Data Centre (IDC). The IDC provides CTBT signatories basic seismic event parameters and a screening analysis indicating whether an event exhibits explosion characteristics (for example, shallow depth). An important component of the screening analysis is a statistical test of the null hypothesis H 0: explosion characteristics using empirical measurements of seismic energy (magnitudes). The established magnitude used for event size is the body-wave magnitude (denoted m b) computed from the initial segment of a seismic waveform. IDC screening analysis is applied to events with m b greater than 3.5. The Rayleigh wave magnitude (denoted M S) is a measure of later arriving surface wave energy. Magnitudes are measurements of seismic energy that include adjustments (physical correction model) for path and distance effects between event and station. Relative to m b, earthquakes generally have a larger M S magnitude than explosions. This article proposes a hypothesis test (screening analysis) using M S and m b that expressly accounts for physical correction model inadequacy in the standard error of the test statistic. With this hypothesis test formulation, the 2009 Democratic Peoples Republic of Korea announced nuclear weapon test fails to reject the null hypothesis H 0: explosion characteristics.

Radionuclide Sensors and Systems for Environmental Monitoring

We have developed automated sensor and monitoring devices for trace radionuclides in water, using preconcentrating columns and radiometric detection. The preconcentrating minicolumn sensor concept combines selective capture and detection in a single functional unit. We have demonstrated quantification of radionuclides such as technetium-99 to levels below drinking water standards in an equilibration-based process that produces steady state signals, signal proportional to concentration, and easy re-equilibration to new concentration levels. Alternatively, monitors can be developed with separate separation and detection units that are fluidically linked. We have demonstrated detection of strontium-90 to levels below drinking water standards by this approach. We are developing autonomous systems for at-site monitoring on the Hanford Site in Washington State.

Radionuclide Sensors and Systems for Environmental Monitoring

not Available.

CHARACTERIZATION OF MINING EXPLOSIONS AT REGIONAL DISTANCES: IMPLICATIONS WITH THE INTERNATIONAL MONITORING SYSTEM

The International Monitoring System (IMS) being constructed in support of the Comprehensive Nuclear‐Test‐Ban Treaty introduces new opportunities to nuclear test monitoring by providing open access to global data from seismic, hydroacoustic, infrasonic, and radionuclide sensors. These sensors will detect myriad natural and man‐made events and can be used to identify those that have explosive characteristics and therefore might be clandestine nuclear tests. Detection and identification of seismic events must be conducted at a lower magnitude threshold (mb = 3.5 and lower) than has been previously considered. Concomitant with the lower monitoring threshold will be an increased number of events that must be scrutinized. This collection will be largely composed of regional observations in which the seismic waves have traversed complex geological structures. High‐fidelity regional, geophysical models will be needed to support accurate location and source identification. Source identification will not be limited to the separation of single‐fired nuclear explosions from earthquakes as in previous testing treaties. The lower‐magnitude threshold and increased reliance on regional observations assures that mining explosions will be detected by the monitoring system. It is important that the signals from mining explosions are properly identified to avoid false alarms of the monitoring system. Cooperation with the mining industry, including deployment of close‐in instrumentation and extensive documentation of the explosions, provides critical information for interpreting the performance of regional discriminants. Linkage of these observations to appropriate physical models of the blasting process is also enhanced through this cooperative research effort. A number of discriminants for characterizing mining explosions have been identified including P to Lg ratios at high and low frequencies, surface wave to high‐frequency body wave amplitudes, Rg at short distances, high‐ and low‐frequency time‐independent spectral modulations, signal correlation, and temporal clustering. Variable performance of individual discriminants results from such factors as mine‐specific blasting practices and the complexity of the regional wave propagation. This variability attests to the need for a suite of region‐specific discriminants. Regional calibration with modest‐size, single‐fired contained chemical explosions can provide a basis for developing region‐specific procedures. Broadband data provide the basis for the most robust set of discriminants. The inclusion of infrasonic data as part of the IMS introduces a potential for the combined use of seismic and infrasonic data for the identification of near‐surface explosions. The generation and, to a greater extent, the propagation of mining explosion infrasonic signals is not well understood, but empirical data attest to its future utility. Evidence for the accidental, near‐simultaneous detonation of a large amount of explosives during standard delay‐fired explosions is presented. Events such as these have single‐fired characteristics and may prove to be problematic in discrimination analysis.

Processing and analysis of infrasound data at the Comprehensive Nuclear Test Ban Treaty International Data Center

The Center for Monitoring Research (CMR) in Arlington, VA served as a prototype of the International Data Center (IDC) that is specified in the Comprehensive Nuclear Test Ban Treaty (CTBT). The CMR developed the software that is now being used by the IDC that has been established in Vienna to acquire, process, and analyze data from the global networks of hydroacoustic, infrasonic, radionuclide, and seismic sensors that are being installed to assist verification of the CTBT. The prototype IDC tested this software and related procedures very extensively with seismic and radionuclide data, but the infrasonic aspects of the system are less advanced due to the limited number of sensors available and a less complete knowledge of sources and signal propagation. The infrasonic processing system attempts to detect signals of interest by combining spatial coherence and power, and estimates signal arrival time, direction of approach, velocity, and other parameters. After a signal is detected, further processing is carried out to try to identify ‘‘phases’’ that correspond to reflections from different atmospheric layers. Finally, detections at multiple sensors of all types (seismic and hydroacoustic as well as infrasonic) are combined to estimate the time and location of potential sources.

NAS Finds No Flaws in Nuclear Treaty

NAS Finds No Flaws in Nuclear Treaty

Hot topics in physical acoustics

With the adoption of the 1996 Comprehensive Nuclear-Test-Ban Treaty, a global International Monitoring System of 321 monitoring stations is being deployed around the world. Three of the four types of sensors used by these stations are acoustical in nature. Seismic, hydroacoustic, infrasonic, as well as radionuclide sensors are used to detect banned underground, underwater, and atmospheric nuclear tests. The infrasonic sensors are arrays 1 to 3 kilometers across to lower their sensitivity to noise from the wind. They can detect nuclear blasts thousands of kilometers away, but they also detect some background events that are interesting too: meteorites, explosive volcanoes, supersonic aircraft, and reentering space debris.

Policing the Peace

S teven R. Bratt's belt started chirping as if on cue, precisely as he was boasting about a new global watchdog system for detecting nuclear tests. Bratt, a seismologist with the U.S. Department of Defense, retrieved the beeper from his hip and studied it for a few seconds. I've got an alert. It's from Lop Nor. Lop Nor is the Chinese test site, he explained. Two stations in a worldwide network of seismometers had just picked up vibrations emanating from central Asia, near China's known nuclear facility. The shock was small, about magnitude 3.5. In bomb equivalents, it would correspond to less than a half kiloton explosion. In this case, however, Bratt suspected the alert was just a minor earthquake. Timing provided an important clue: The shock had originated at 12:19 Greenwich Mean Time, which is not the kind of round, on-the-hour time that countries usually choose for performing a major weapon test. Seismic analysts would later confirm Bratt's hunch when they determined that the Chinese vibrations actually originated at an unlikely place to stage a test, hundreds of kilometers away from the Lop Nor site. The impromptu demonstration nonetheless made a good advertisement for the new international monitoring system-an ever-vigilant network of sensors strung around the globe, listening, sniffing, and waiting. The system, which currently includes 140 stations, is a prototype of the one required by the Comprehensive Test Ban Treaty (CTBT), currently being negotiated in Geneva. After nearly 40 years of discussion, the world is moving toward adopting the treaty-if all goes well-as early as this summer, thereby prohibiting all nuclear testing. To back up a ban on nuclear testing, the treaty calls for a four-part monitoring system consisting of seismic, hydroacoustic, infrasound, and atmospheric radionuclide sensors. According to sections of the treaty already written, all the data collected by this system will flow into an information hub called the International Data Center, a prototype of which is located in Arlington, Va. Bratt is the Defense Department's program director overseeing development of the data center. Each element of the monitoring arsenal will patrol a different region of the planet, though they overlap to some degree. The seismic network, the backbone of the system, will draw on 50 primary and 120 auxiliary stations to pick up vibrations from any underground tests. The hydroacoustic system will keep watch for ocean blasts using six underwater sound receivers tied in with five islandbased seismometers. An infrasound network of 60 microbarographic pressure sensors will listen for atmospheric explosions. Lastly, 75 radionuclide stations will monitor the winds for the distinctive isotopic aroma vented into the atmosphere by atomic blasts.