26 research outputs found
Background and Anomaly Learning Methods for Static Gamma-ray Detectors
Static gamma-ray detector systems that are deployed outdoors for radiological
monitoring purposes experience time- and spatially-varying natural backgrounds
and encounters with man-made nuisance sources. In order to be sensitive to
illicit sources, such systems must be able to distinguish those sources from
benign variations due to, e.g., weather and human activity. In addition to
fluctuations due to non-threats, each detector has its own response and energy
resolution, so providing a large network of detectors with predetermined
background and source templates can be an onerous task. Instead, we propose
that static detectors use simple physics-informed algorithms to automatically
learn the background and nuisance source signatures, which can them be used to
bootstrap and feed into more complex algorithms. Specifically, we show that
non-negative matrix factorization (NMF) can be used to distinguish static
background from the effects of increased concentrations of radon progeny due to
rainfall. We also show that a simple process of using multiple gross count rate
filters can be used in real time to classify or ``triage'' spectra according to
whether they belong to static, rain, or anomalous categories for processing
with other algorithms. If a rain sensor is available, we propose a method to
incorporate that signal as well. Two clustering methods for anomalous spectra
are proposed, one using Kullback-Leibler divergence and the other using
regularized NMF, with the goal of finding clusters of similar spectral
anomalies that can be used to build anomaly templates. Finally we describe the
issues involved in the implementation of some of these algorithms on deployed
sensor nodes, including the need to monitor the background models for long-term
drifting due to physical changes in the environment or changes in detector
performance.Comment: 12 pages, 6 figures, accepted for publication in IEEE Transactions on
Nuclear Scienc
3D Gamma-ray and Neutron Mapping in Real-Time with the Localization and Mapping Platform from Unmanned Aerial Systems and Man-Portable Configurations
Nuclear Scene Data Fusion (SDF), implemented in the Localization and Mapping
Platform (LAMP) fuses three-dimensional (3D), real-time volumetric
reconstructions of radiation sources with contextual information (e.g. LIDAR,
camera, etc.) derived from the environment around the detector system. This
information, particularly when obtained in real time, may be transformative for
applications, including directed search for lost or stolen sources, consequence
management after the release of radioactive materials, or contamination
avoidance in security-related or emergency response scenarios. 3D
reconstructions enabled by SDF localize contamination or hotspots to specific
areas or objects, providing higher resolution over larger areas than
conventional 2D approaches, and enabling more efficient planning and response,
particularly in complex 3D environments.
In this work, we present the expansion of these gamma-ray mapping concepts to
neutron source localization. Here we integrate LAMP with a custom
(CLLBC) scintillator detector sensitive to both
gamma-rays and neutrons, which we dub Neutron Gamma LAMP (NG-LAMP). NG-LAMP
enables simultaneous neutron and gamma-ray mapping with high resolution
gamma-ray spectroscopy. We demonstrate the ability to detect and localize
surrogate Special Nuclear Materials (SNM) in real-time and in 3D based on
neutron signatures alone, which is critical for the detection of heavily
shielded SNM, when gamma-ray signatures are attenuated. In this work, we show
for the first time the ability to localize, in 3D and realtime, a neutron
source in the presence of a strong gamma-ray source, simultaneous and
spectroscopic localization of three gamma-ray sources and a neutron source, and
finally the localization of a surrogate SNM source based on neutron signatures
alone, where gamma-ray data are consistent with background
A quantum isomonodromy equation and its application to N=2 SU(N) gauge theories
We give an explicit differential equation which is expected to determine the
instanton partition function in the presence of the full surface operator in
N=2 SU(N) gauge theory. The differential equation arises as a quantization of a
certain Hamiltonian system of isomonodromy type discovered by Fuji, Suzuki and
Tsuda.Comment: 15 pages, v2: typos corrected and references added, v3: discussion,
appendix and references adde
Instanton partition functions in N=2 SU(N) gauge theories with a general surface operator, and their W-algebra duals
We write down an explicit conjecture for the instanton partition functions in
4d N=2 SU(N) gauge theories in the presence of a certain type of surface
operator. These surface operators are classified by partitions of N, and for
each partition there is an associated partition function. For the partition N=N
we recover the Nekrasov formalism, and when N=1+...+1 we reproduce the result
of Feigin et. al. For the case N=1+(N-1) our expression is consistent with an
alternative formulation in terms of a restricted SU(N)xSU(N) instanton
partition function. When N=1+...+1+2 the partition functions can also be
obtained perturbatively from certain W-algebras known as quasi-superconformal
algebras, in agreement with a recent general proposal.Comment: 20 page
Radiation processing for cultural heritage preservation : Romanian experience
Radiation sterilization has been considered a mass decontamination technique for biodegradable cultural heritage (CH) since its widespread application in the medical field. Initial experiments have revealed advantages, for example, efficiency and effectiveness, but also disadvantages, namely “side effects” concerning CH materials. More than 50 years later, the adequacy of ionizing radiation for some CH artefacts is still the subject of discussion. The main reason why is that science and industry are not yet able to provide a more efficient technique for treating mass decontamination. For wooden items, there is general agreement that the irradiation dose required for insect eradication is not damaging, even in the case of polychromed wood. For cellulose pulp (paper), there is a reduction in polymerization degree (DP) at the high doses necessary to stop the attack of fungi, but this should be considered taking into account the purpose of the treatment. Emergency or rescue treatments are necessary to mitigate the consequences of accidents or improper storage conditions. In some cases (archives), the value of written information is greater than the historical value of the paper support. For other materials, namely textiles, leather and parchment, less research has been published on the effect of ionizing radiation treatment. As a general rule, irradiation is not necessary when only a few CH elements are present that are affected by biological contamination since restorers can solve the problem by classical means. The need for radiation treatment arises when large collections (hundreds, thousands or even more elements) are heavily affected by the biological attack. In Romania, the IRASM gamma irradiator of IFIN-HH is receiving an increasing number of requests for CH treatment, mainly due to an intensive research programme concerning this topic and close liaison with CH owners or administrators. Besides reviewing the scientific results obtained in Romania and abroad, this paper presents some examples from experiences in Romania
Effects of nanosecond laser pulses at 248 nm wavelength on multilayer CrN/(Cr,V)N coatings
The effects of UV nanosecond laser pulses on multilayer CrN/(Cr,V)N coatings were studied. In the experiment laser irradiation was performed in air at 248 nm wavelength and pulse duration of 25 ns. The surface composition and microstructure was analyzed depending on the initial content of vanadium in the coatings and number of accumulated laser pulses at a fluence of 0.17 Jcm-2 . Most of the absorbed laser energy was rapidly transformed into heat, producing intensive modifications of the composition and morphology of the multilayer structure.The result has shown that concentration of metallic components was homogeneously distributed inside the coatings. However, on the surface and in the sub-surface regions the contents of Cr and V were decreased due to oxidation. The composition and thickness of created mixture of oxides Cr2O3 and V2O5 depend on the number of laser pulses and initial V content. Laser induced surface morphology changes of the multilayer CrN/(Cr,V)N coatingswere registered at the irradiation areas: (i) grainy structures at peripheries, (ii) cracks and (iii) irregular closed shapes in the center.VI International School and Conference on Photonics and COST actions: MP1406 and MP1402 : PHOTONICA2017 : program and the book of abstracts; August 23 - September 1, 2017; Belgrad
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Polaris-LAMP: Multi-Modal 3-D Image Reconstruction with a Commercial Gamma-Ray Imager
The Polaris-LAMP multi-modal 3-D gamma-ray imager is a radiation mapping and imaging platform which uses a commercial off-the-shelf (COTS) detector integrated with a contextual sensor localization and mapping platform. The integration of these systems enables a free-moving radiation imaging capability with proximity mapping, coded-aperture, and Compton imaging modalities, which can create 3-D reconstruction of photon sources from tens of keV to several MeV. Gamma-ray events are recorded using a segmented cadmium zinc telluride (CZT) detector (Polaris-H Quad by H3D Inc., Ann Arbor, MI, USA), while scene data are derived from a contextual sensor and computation package developed by Lawrence Berkeley National Laboratory which includes GPS, laser ranging, and inertial measurement sensors. An onboard computer uses these inputs to create rapidly updating pose (10 Hz) and 3-D scene estimates using a simultaneous localization and mapping (SLAM) algorithm. The precise gamma-ray event location and timing resolution of the Polaris CZT sensor enables Compton imaging above several hundred keV, while photon sources at lower images are localized using coded-aperture imaging techniques. The multi-modal imaging concept enables imaging of diverse radiation sources spanning from the 59-keV emission of 241Am to the 1.1 and 1.3 MeV lines of 60Co. This work focuses on the description of the operational principles of the detector system and demonstrating the 3-D imaging performance in a variety of source detection and mapping scenarios. As a proof of concept, we demonstrate mapping complex environments, including both point source and distributed-source environments using proximity, coded-aperture, and Compton imaging modalities. Furthermore, we show the successful use of the system to perform measurements in high-background environments through analysis of arrays of uranium hexafluoride cylinders at the Paducah UF6 project site
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3-D Object Tracking in Panoramic Video and LiDAR for Radiological Source-Object Attribution and Improved Source Detection
Networked detector systems can be deployed in urban environments to aid in the detection and localization of radiological and/or nuclear material. However, effectively responding to and interpreting a radiological alarm using spectroscopic data alone may be hampered by a lack of situational awareness, particularly in complex environments. This study investigates the use of Light Detection and Ranging (LiDAR) and streaming video to enable real-time object detection and tracking, and the fusion of this tracking information with radiological data for the purposes of enhanced situational awareness and increased detection sensitivity. This work presents an object detection, tracking, and novel source-object attribution analysis that is capable of operating in real time. By implementing this analysis pipeline on a custom-developed system that comprises a static 2 in. \times 4 in. \times16 in. NaI(Tl) detector colocated with a 64-beam LiDAR and four monocular cameras, we demonstrate the ability to accurately correlate trajectories from tracked objects to spectroscopic gamma-ray data in real time and use physics-based models to reliably discriminate between source-carrying and nonsource-carrying objects. In this work, we describe our approach in detail and present a quantitative performance assessment that characterizes the source-object attribution capabilities of both video and LiDAR. Additionally, we demonstrate the ability to simultaneously track pedestrians and vehicles in a mock urban environment and use this tracking information to improve both detection sensitivity and situational awareness using our contextual-radiological data fusion methodology
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Improved Gamma-Ray Point Source Quantification in Three Dimensions by Modeling Attenuation in the Scene
Using a series of detector measurements taken at different locations to localize a source of radiation is a well-studied problem. The source of radiation is sometimes constrained to a single point-like source, in which case the location of the point source can be found using techniques such as maximum likelihood. Recent advancements have shown the ability to locate point sources in 2-D and even 3-D but few have studied the effect of intervening material on the problem. In this work, we examine gamma-ray data taken from a freely moving system and develop voxelized 3-D models of the scene using data from its onboard light detection and ranging (LiDAR) unit. Ray casting is used to compute the distance each gamma ray travels through the scene material, which is then used to calculate attenuation assuming a single attenuation coefficient for solids within the geometry. Parameter estimation using maximum likelihood is performed to simultaneously find the attenuation coefficient, source activity, and source position that best match the data. Using a simulation, we validate the ability of this method to reconstruct the true location and activity of a source, along with the true attenuation coefficient of the structure it is inside, and then we apply the method to measured data with sources and find good agreement