Special nuclear material detection with a mobile multi-detector system

The detection of special nuclear material has been studied with a mobile inspection system used both as a high sensitivity passive neutron/gamma spectroscopic tool and as an active inspection device using tagged neutrons. The detection of plutonium samples seems to be possible with passive interrogation, even for small samples, thanks to the yield of gamma ray and neutrons. Moreover the gamma ray spectrum shows clear signatures related to ²³⁹Pu. The passive detection of uranium is much more difficult because of the low neutron yield and of the easiness of shielding the gamma ray yield of highly enriched U samples. However, we show that active interrogation with tagged neutrons is able to provide signatures for the discrimination of uranium against other heavy metals.     

High-fidelity MCNP modeling of a D-T neutron generator for active interrogation of special nuclear material

Fast and robust methods for interrogation of special nuclear material (SNM) are of interest to many agencies and institutions in the United States. It is well known that passive interrogation methods are typically sufficient for plutonium identification because of a relatively high neutron production rate from ²⁴⁰Pu [1]. On the other hand, identification of shielded uranium requires active methods using neutron or photon sources [2]. Deuterium-deuterium (2.45 MeV) and deuterium-tritium (14.1 MeV) neutron-generator sources have been previously tested and proven to be relatively reliable instruments for active interrogation of nuclear materials [3] and [4]. In addition, the newest generators of this type are small enough for applications requiring portable interrogation systems.Active interrogation techniques using high-energy neutrons are being investigated as a method to detect hidden SNM in shielded containers [4] and [5]. Due to the thickness of some containers, penetrating radiation such as high-energy neutrons can provide a potential means of probing shielded SNM. In an effort to develop the capability to assess the signal seen from various forms of shielded nuclear materials, the University of Michigan Neutron Science Laboratory’s D-T neutron generator and its shielding were accurately modeled in MCNP. The generator, while operating at nominal power, produces approximately 1×10¹⁰ neutrons/s, a source intensity which requires a large amount of shielding to minimize the dose rates around the generator. For this reason, the existing shielding completely encompasses the generator and does not include beam ports. Therefore, several MCNP simulations were performed to estimate the yield of uncollided 14.1-MeV neutrons from the generator for active interrogation experiments. Beam port diameters of 5, 10, 15, 20, and 25 cm were modeled to assess the resulting neutron fluxes. The neutron flux outside the beam ports was estimated to be approximately 2×10⁴ n/cm² s.     

Nuclear detection to prevent or defeat clandestine nuclear attack

Countering clandestinely delivered nuclear and radiological threats requires a multielement, global, civil/military, system-of-systems approach. One important element is geographically layered, sensor-based detection of threat objects, including radiation detection systems. An effective defense against these threats should take advantage of the latest developments in radiation detection technology. This paper reviews the physics of nuclear detection, and points out areas where improvements can be anticipated, via case studies of technologies such as gamma-ray imaging, advanced radiography, large-area detectors, and active interrogation.     

探测爆炸物和放射性材料的核技术方法

叙述了采用核技术方法探查隐藏爆炸物和放射性材料的优越性及其特点,重点介绍了8类主动式中子质询技术,对它们探查爆炸物的适用范围进行了剖析,对采用伽玛法的非中子质询技术作了一般性讨论.概括了各类已商用化工业中子源和伽玛射线探测器,论述了它们应用于安检系统的长处和不足.分析了两类典型的隐藏爆炸物安检问题,指出一个理想的爆炸物探查系统应具备的11项特性.介绍了国际上最受重视的伴随粒子成像和脉冲快中子系统的研制进展.简要描述了有别于主动式探查爆炸物的被动式放射性材料探查方法.指出隐藏爆炸物品和放射性物质的检查没有一种方法是万能的,不同场合不同目标需要用不同的技术或联合使用几种技术.     

Fatigue damage discrepancies,the intrinsic fatigue damage map locus and the multiple stages of the similitude concept

The work demonstrates how the theory of the fatigue damage map (FDM) can be used in order to define a closed form locus where fatigue crack growth can be sought. The Intrinsic FDM Locus depending only on readily material properties represents a tool able to accurately predict crack growth of polycrystals. If the Locus is expressed in terms of a surface plot after triangulation of the data, it concludes into visualization of the potential for multiple similitude stages. The stages are defined as a function of the maximum far field stress and ΔK. Multiple similitude stages are found to dominate the short and near threshold area (Stage I growth) and represent direct result of the effect of polycrystalline behaviour to flow resistance. The work concludes that interrogation of the points defining the Intrinsic FDM Locus and related to the three thresholds can provide potential characteristics in the quest for an ideal damage tolerance material.     

Simulation methods for photoneutron-based active interrogation systems

Modeling methods have been developed to accelerate the simulation of a photoneutron-based active interrogation system of nuclear materials. The proposed technique segments the simulation of a full system into several physical steps, representing functional approximations. Each approximation is carried-out separately, resulting in a major reduction in computational time and a significant improvement in tally statistics. Although more human effort is required to separate each step, the net time required to produce results is drastically reduced. In addition, the results of previous steps can be used as inputs to proceeding steps without the need for re-simulation. We show that for a photoneutron interrogation system, the final results are in good agreement with the full, single-step simulation and also with experimental results.     

Computer-aided design of rolling mills

Computers have been used for design of rolling mills since 1960s. Easy access to high speed digital computers has facilitated use of more accurate rolling theories for design work and comprehensive computer simulations have been developed for all types of mills. These simulations include optimization of roll pass sequence, calculation of roll force, torque and temperature and detailed time studies for productivity calculations. These aspects of mill simulation are examined with specific examples. In the design of rolling mills equipment, computer-aided design has been widely used. The available software, which covers both steady state and dynamic analysis of items such as mill stands, drive systems, manipulators, cooling beds, roll cooling, and automatic gauge control systems, is reviewed with special reference to the nature of analysis and range of applications. Computer drafting is being increasingly used by rolling mills designers for both interactive and non-interactive applications. The integration of computer graphics with the design software holds promise for improving the productivity and creativity of designers and is an active area of development in rolling mills design organizations. A specific application where such integration has been achieved is discussed.     

Recent advancements in urea biosensors for biomedical applications

The quick progress in health care technology as a recurrent measurement of biochemical factors such as blood components leads to advance development and growth in biosensor technology necessary for effectual patient concern. The review wok of authors present a concise information and brief discussion on the development made in the progress of potentiometric, field effect transistor, graphene, electrochemical, optical, polymeric, nanoparticles and nanocomposites based urea biosensors in the past two decades. The work of authors is also centred on different procedures/methods for detection of urea by using amperometric, potentiometric, conductometric and optical processes, where graphene, polymer etc. are utilised as an immobilised material for the fabrication of biosensors. Further, a comparative revision has been accomplished on various procedures of urea analysis using different materials‐based biosensors, and it discloses that electrochemical and potentiometric biosensor is the most promise one among all, in terms of rapid response time, extensive shelf life and resourceful design.     

Surrogates of plutonium for detection equipment testing

Fight against illicit trafficking of nuclear material relies on the possibility to detect nuclear material concealed in vehicles, people or cargo containers. This is done by equipping and training law enforcement and security staff in border stations or other points of access to strategic places and critical infrastructures with radiation detection equipment.The design, development, testing and evaluation of these instruments ideally require the use of real nuclear material to assess, verify and certify their detection performance. Availability of special nuclear material may be an issue, especially for industry, since only few specialized laboratories are licensed for such material.This paper tries to analyse and describe the possibility to use suitable surrogates that may replace the use of real nuclear material in testing the detection capabilities of instruments used in nuclear security.     

Determination of optical probe interrogation field of near-infrared reflectance: phantom and Monte Carlo study

An optical probe used to localize human brain tissues in vivo has been reported previously. It was able to sense the underlying tissue structure with an optical interrogation field, termed as "look ahead distance" (LAD). A new side-firing probe has been designed with its optical window along its side. We have defined the optical interrogation field of the new side probe as "look aside distance" (LASD). The purpose of this study is to understand the dependence of the LAD and LASD on the optical properties of tissue, the light source intensity, and the integration time of the detector, using experimental and computational methods. The results show that a decrease in light intensity does decrease the LAD and LASD and that an increase in integration time of detection may not necessarily improve the depths of LAD and LASD. Furthermore, Monte Carlo simulation results suggest that the LAD/LASD decreases with an increase in reduced scattering coefficient to a point, after which the LAD/LASD remains constant. We expect that an optical interrogation field of a tip or side probe is approximately 1-2 mm in white matter and 2-3.5 mm in gray matter. These conclusions will help us optimally manipulate the parameter settings during surgery and determine the spatial resolution of the probe.     

Algorithms and tools for the preprocessing of LC-MS metabolomics data

Metabolomics encompasses the study of small molecules in a biological sample. Liquid Chromatography coupled with Mass Spectrometry (LC-MS) profiling is an important approach for the identification and quantification of metabolites from complex biological samples. The amount and complexity of data produced in an LC-MS profiling experiment demand automatic tools for the preprocessing, analysis, and extraction of useful biological information. Data preprocessing—a topic that covers noise filtering, peak detection, deisotoping, alignment, identification, and normalization—is thus an active area of metabolomics research. Recent years have witnessed development of many software for data preprocessing, and still there is a need for further improvement of the data preprocessing pipeline. This review presents an overview of selected software tools for preprocessing LC-MS based metabolomics data and tries to provide future directions.     

Low-loss, silicon integrated, aluminum nitride photonic circuits and their use for electro-optic signal processing

Photonic miniaturization requires seamless integration of linear and nonlinear optical components to achieve passive and active functions simultaneously. Among the available material systems, silicon photonics holds immense promise for optical signal processing and on-chip optical networks. However, silicon is limited to wavelengths above 1.1 μm and does not provide the desired lowest order optical nonlinearity for active signal processing. Here we report the integration of aluminum nitride (AlN) films on silicon substrates to bring active functionalities to chip-scale photonics. Using CMOS-compatible sputtered thin films we fabricate AlN-on-insulator waveguides that exhibit low propagation loss (0.6 dB/cm). Exploiting AlN's inherent Pockels effect we demonstrate electro-optic modulation up to 4.5 Gb/s with very low energy consumption (down to 10 fJ/bit). The ultrawide transparency window of AlN devices also enables high speed modulation at visible wavelengths. Our low cost, wideband, carrier-free photonic circuits hold promise for ultralow power and high-speed signal processing at the microprocessor chip level.     

Photothermal-Switched Single-Atom Nanozyme Specificity for Pretreatment and Sensing

Various applications lead to the requirement of nanozymes with either specific activity or multiple enzyme-like activities. To this end, intelligent nanozymes with freely switching specificity abilities hold great promise to adapt to complicated and changeable practical conditions. Herein, a nitrogen-doped carbon-supported copper single-atom nanozyme (named Cu SA/NC) with switchable specificity is reported. Atomically dispersed active sites endow Cu SA/NC with specific peroxidase-like activity at room temperature. Furthermore, the intrinsic photothermal conversion ability of Cu SA/NC enables the specificity switch by additional laser irradiation, where photothermal-induced temperature elevation triggers the expression of oxidase-like and catalase-like activity of Cu SA/NC. For further applications in practice, a pretreatment-and-sensing integration kit (PSIK) is constructed, where Cu SA/NC can successively achieve sample pretreatment and sensitive detection by switching from multi-activity mode to specific-activity mode. This study sets the foundation for nanozymes with switchable specificity and broadens the application scope in point-of-care testing.     

A review of wireless SAW sensors

Wireless measurement systems with passive surface acoustic wave (SAW) sensors offer new and exciting perspectives for remote monitoring and control of moving parts, even in harsh environments. This review paper gives a comprehensive survey of the present state of the measurement systems and should help a designer to find the parameters required to achieve a specified accuracy or uncertainty of measurement. Delay lines and resonators have been used, and two principles have been employed: SAW one-port devices that are directly affected by the measurand and SAW two-port devices that are electrically loaded by a conventional sensor and, therefore, indirectly affected by the measurand. For radio frequency (RF) interrogation, time domain sampling (TDS) and frequency domain sampling (FDS) have been investigated theoretically and experimentally; the methods of measurement are described. For an evaluation of the effects caused by the radio interrogation, we discuss the errors caused by noise, interference, bandwidth, manufacturing, and hardware tuning. The system parameters, distance range, and measurement uncertainty are given numerically for actual applications. Combinations of SAW sensors and special signal processing techniques to enhance accuracy, dynamic range, read out distance, and measurement repetition rate (measurement bandwidth) are presented. In conclusion, an overview of SAW sensor applications is given.     

Stabilizing intermetallic phases within aluminum foam

Because of ambiguity in microstructural characterization of cell wall material of Alporas® aluminum foam in literature until now, the study was focused to contribute to the examination of microstructural variability, and to reveal differences in distribution of stabilizing intermetallic phases in microstructure and their identification. It was shown that the microstructure consists of four precipitates distributed in α-Al matrix. The energy-dispersive X-ray spectroscopy revealed the presence of precipitates with compositions of AlCa, AlCaTi, AlCaFe and AlCaTiFe. However, selected area electron diffraction and X-ray diffraction confirmed that all analyzed precipitates could be indexed only in terms of tetragonal Al₄Ca or cubic Al₂₀CaTi₂. It was shown that the distribution of intermetallic compounds in cell wall material is affected by height position in the foamed block — they are either distributed along the grain boundaries of α-Al in the bottom area or they are dispersed in the α-Al matrix in the middle and top area.     

Local oscillator limited frequency stability for passive atomic frequency standards using square wave frequency modulation

Atomic frequency standards using square wave frequency modulation effectively interrogate the atomic line by switching back and forth between two frequencies with equal atomic absorption values. For a symmetric absorption line, the slope of the responses will also be equal. In the quasistatic limit, this would seem to be an ideal interrogation process: the sign reversal of frequency slope can be removed by detection electronics to give an essentially unvarying sensitivity to local oscillator frequency variations. Such an interrogation would seem to eliminate L.O. aliasing and relieve stringent requirements on L.O. phase noise. Nevertheless, sign changes in the interrogation and detection processes mean that the sensitivity is actually zero at some point in the cycle. We derive consequences of this fact by an analysis in terms of the sensitivity function g(t). For white phase noise, we derive an optimal form for g(t) and show that the aliased noise always diverges as g(t) approaches a constant. For flicker phase noise, we find a limiting form that could, in principle, eliminate the aliasing effect; in practice, however, the improvement is limited by a slow dependence on available bandwidth. Finally, we derive optimized forms for any phase noise spectrum.     

Identifying permafrost slope disturbance using multi-temporal optical satellite images and change detection techniques

Active layer detachments (ALDs) are a common form of permafrost slope disturbance that pose a serious risk for infrastructure and can impact environmental and ecological stability in Arctic regions. Effective recognition and detection of slope disturbances are critical for future hazard analysis. Historically, this has primarily been done through manual image interpretation and field mapping, both of which are cost-intensive. Semi-automatic detection techniques have been successfully applied in more temperate regions to identify slope failures, however, little work has been done to map permafrost disturbances. In this paper we present a methodology to detect and map ALDs using multi-temporal IKONOS satellite imagery in combination with vegetation index differencing and object-based image analysis, to semiautomatically identify landscape change associated with ALDs. A normalized difference vegetation index (NDVI) was computed for each of the two dates (2004 and 2010) and then subtracted generating a NDVI difference surface. Using areas where vegetation was removed as a proxy for the presence of ALDs, a multi-resolution segmentation algorithm was used to threshold the NDVI difference map into objects to demarcate regions of similarity (i.e., potential ALDs). To discriminate between disturbed and undisturbed zones a NDVI threshold was applied removing false positives. The thresholded image was then verified with a disturbance inventory collected from the field. These methods were successfully applied to the study area achieving 43% detection accuracy when identifying all ALDs. Morphometric characteristics were used to separate ALDs into two forms, elongate and compact, with accuracies assessed for each. Elongate ALDs, with a detection accuracy of 67%, are typically more destructive, moving substantially more material downslope over longer distances and posing a greater risk for infrastructure. By contrast, compact ALDs are associated with minimal downslope sliding distances (< 1 m to several meters) and result in little to no extension in the scar zone and thus limited downslope material movement. The method used in this study detected only 7% of compact disturbances indicating that morphology and size are important variables when detecting ALDs. These results collectively show promise for the semi-automated detection of slope disturbances (i.e., elongate ALDs) in permafrost settings and a cost-effective method to delineate areas for more detailed hazard assessment methods.     

Carbon monoxide detector fabricated on the basis of a tin oxide novel doping method

Toxic gas detection is a common issue of interest in domestic as well as industrial environments. There are, in fact, accurate methods to measure gas concentrations (Fourier transform infrared, gas chromatographs, or mass spectrometers) but they are too expensive and require skilled operators. Therefore, these complex detection systems are not useful for many applications, such as hazardous gas level detection in domestic appliances. In this paper, investigations lead to the fabrication of a micromachined tin oxide device for carbon monoxide detection in domestic environments. Relevant parameters that influence gas detection are analyzed and thus the device fabrication process defined by means of microtechnologies. Throughout the material optimization for CO detection, three different additive adding methods by dc sputtering PVD technique are studied and compared for two additives: Pt and Pd.     

Meshfree and finite element nodal integration methods

Nodal integration can be applied to the Galerkin weak form to yield a particle‐type method where stress and material history are located exclusively at the nodes and can be employed when using meshless or finite element shape functions. This particle feature of nodal integration is desirable for large deformation settings because it avoids the remapping or advection of the state variables required in other methods. To a lesser degree, nodal integration can be desirable because it relies on fewer stress point evaluations than most other methods. In this work, aspects regarding stability, consistency, efficiency and explicit time integration are explored within the context of nodal integration. Both small and large deformation numerical examples are provided. Copyright © 2007 John Wiley & Sons, Ltd.