Papers by Per Andreas Enqvist
2022 IEEE Conference on Virtual Reality and 3D User Interfaces Abstracts and Workshops (VRW)
Behavior-based authentication methods are actively being developed for XR. In particular, gaze-ba... more Behavior-based authentication methods are actively being developed for XR. In particular, gaze-based methods promise continuous au-thentication of remote users. However, gaze behavior depends on the task being performed. Identification rate is typically highest when comparing data from the same task. In this study, we compared authentication performance using VR gaze data during random dot viewing, 360-degree image viewing, and a nuclear training simu-lation. We found that within-task authentication performed best for image viewing (72%). The implication for practitioners is to integrate image viewing into a VR workflow to collect gaze data that is viable for authentication.
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Transactions of the American Nuclear Society, 2016
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2017 International Conference on 3D Vision (3DV), 2017
Tracking radioactive sources in large spaces has applications for homeland security, airport and ... more Tracking radioactive sources in large spaces has applications for homeland security, airport and port surveillance as well as military and security uses. Unfortunately, source localizing radiological detectors are extremely expensive, and those with low prices are isotropic - i.e. they integrate radiation from a sphere of directions centered at the sensor. In this paper, we show that omnidirectional depth sensors and isotropic radiological detectors have complementary strengths and can enable many applications. We model the source strength of radiological sources and integrate these with LIDAR measurements and a Kalman filter tracker. This enables applications such as tracking behind walls and detecting multiple radiological sources in the same scene.
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Transactions of the American Nuclear Society, 2016
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2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2017
Thermal neutron imaging technique was developed using the 100 kW University of Florida Training R... more Thermal neutron imaging technique was developed using the 100 kW University of Florida Training Reactor and a CCD neutron camera at the University of Florida. The 200 × 200 mm scintillator used in the neutron camera was a 0.2 mm thick $^{6}$f LiF:ZnS screen. The thermal column beam port of the reactor was modified for collimation and was used to produce the neutron images. Different reactor power levels were chosen depending on the samples ranging from 100 W to 4000 W. Thermal neutron images of different sample objects like flower bouquet inside a lead cask, ASTM standards, turbine blade, small gearbox and water valve were acquired. The acquisition times range from 2 to 5 min for the samples discussed in this paper.
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Recently, the Helium-4 gas fast neutron scintillation detectors is being used in time-sensitive m... more Recently, the Helium-4 gas fast neutron scintillation detectors is being used in time-sensitive measurements, such time-of-flight and multiplicity counting. In this paper, a set of time aligned signals was acquired in a coincidence measurement using the Helium-4 gas detectors and EJ-309 liquid scintillators. The high-speed digitizer system is implanted with a trigger moving average window (MAW) unit combing with its constant fraction discriminator (CFD) feature. It can calculate a “time offset” to the timestamp value to get a higher resolution timestamp (up to 50 ps), which is better than the digitizer's time resolution (4 ns) [1]. The digitized waveforms were saved to the computer hard drive and post processed with digital analysis code to determine the difference of their arrival times. The full-width at half-maximum (FWHM) of the Gaussian fit was used as to examine the resolution. For the cascade decay of Cobalt-60 (1.17 and 1.33 MeV), the first version of the Helium-4 detect...
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Passive methods of nuclear safeguards determine the important parameters of an unknown sample fro... more Passive methods of nuclear safeguards determine the important parameters of an unknown sample from the statistics of the detection of the neutrons emitted from the item. These latter are mostly due to spontaneus fissions (and (α,n) reactions, neglected here), enhanced by a slight internal multiplication before leaking out. Following the original work of Bohnel [1], the methodology of traditional multiplicity counting is based on the first three factorial moments of the number of neutrons, emitted from the sample due to one source event. These “Bohnel moments” were derived in the so-called “point model”, in which no space-dependence is assumed, rather a uniform first collision probability is assumed for each neutron, irrespective of the position of its birth and its velocity direction. The purpose of the present work is to derive the same factorial moments in a one-speed space-dependent model, in which the position and direction of the neutrons is accounted for, but (similarly to the...
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2018
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2017
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IEEE Transactions on Nuclear Science, 2011
ABSTRACT A measurement system capable of multiplicity measurements for both neutrons and gamma ra... more ABSTRACT A measurement system capable of multiplicity measurements for both neutrons and gamma rays has been developed. The benefit of such an approach is in the increased number of available observables. A pure neutron assay results in three observables for third-order multiples, while a combined neutron/gamma-ray assay results in nine observables for the same order of multiples. The idea is to use the additional observables to achieve greater accuracy when determining unknown parameters of the sample such as the fissile mass. The measurement system is based on liquid scintillation detectors (EJ-309s) which feed detected pulses to a digital data-acquisition system. The excellent pulse shape discrimination capabilities of the EJ-309s allow for accurate differentiation between gamma-ray pulses and neutron pulses. The PSD is vital to correctly identify the different multiples up to the third order: n, γ , nn, nγ , γγ , nnn, nnγ , nγγ and γγγ . Previous investigation of the measurement system showed that good counting statistics can be achieved within minutes for spontaneous-fission sources such as 252Cf. In this paper, we present new measurement results and corresponding Monte Carlo simulations aimed at characterizing the measurement system. Comparison of the measured and simulated multiples is discussed in detail and a relatively good agreement is found.
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2015 International Conference on 3D Vision, 2015
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Physical Review C
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EPJ Web of Conferences
Neutron scatter cameras are a type of directional neutron detectors that rely on multiple neutron... more Neutron scatter cameras are a type of directional neutron detectors that rely on multiple neutron scatters to generate images that can reveal the direction and distribution of neutron sources. Fast neutron cameras which have recently been developed rely on multiple detector volumes and make use of neutron time-of-flight measurements. These designs, though effective in localizing the source direction, relies on a large amount of detection and electrical equipment, thus increasing size, cost, and complexity of the systems to unreasonable levels for some applications. This project seeks to develop a compact scatter camera that is less expensive than systems relying on multiple detector volumes. Crucially, two components and capabilities are needed to achieve this: fast scintillation detection materials and picosecond electrical pulse timing. Utilizing such electronics, distinguishing between scintillation light pulses generated by the same neutron within one detector volume is possible...
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Applied Radiation and Isotopes
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EPJ Web of Conferences
The University of Florida is taking a multidisciplinary approach to fuse the data between 3D visi... more The University of Florida is taking a multidisciplinary approach to fuse the data between 3D vision sensors and radiological sensors in hopes of creating a system capable of not only detecting the presence of a radiological threat, but also tracking it. The key to developing such a vision-aided radiological detection system, lies in the count rate being inversely dependent on the square of the distance. Presented in this paper are the results of the calibration algorithm used to predict the location of the radiological detectors based on 3D distance from the source to the detector (vision data) and the detectors count rate (radiological data). Also presented are the results of two correlation methods used to explore source tracking.
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IEEE Transactions on Nuclear Science
Finding and tracking radioactive sources have numerous security applications in civilian energy i... more Finding and tracking radioactive sources have numerous security applications in civilian energy installations, military facilities, and ports of entry. The price of radiological sensors varies proportionally to size and imaging characteristics such as angular resolution, and the cheapest devices are nearly isotropic–i.e., they integrate radiation from a sphere of directions centered at the sensor. While many radiation sensors have high aspect ratios or odd shapes, the sensors used here are right cylinders, with a near identical directional efficiency such that for analysis purposes, other aspects, such as counting statistics, would make nonisotropy of the sensor negligible. In this article, we propose a simple and robust way to integrate measurements from both isotropic radiological sensors and depth sensors, whose reliability and resolution benefit from recent advances in computer vision and imaging. Our key idea is to convert all sensor measurements into proximity signals based on radial distance variations over time. Based on this sensor fusion model, we show that for moving radiological sources even a simple Kalman filter can trade-off the complementary strength of high-resolution depth sensors and isotropic radiological sensors. We show novel results with a LIDAR sensor and a thermal stereo pair, and demonstrate applications such as tracking and rendering non-line-of-sight imagery behind obstacles and detecting multiple radiological sources in the same scene.
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Papers by Per Andreas Enqvist