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Showing posts with label University of Maryland. Show all posts
Showing posts with label University of Maryland. Show all posts
After a nuclear power plant accident, for safety reasons it can be difficult for humans or even robots to get close enough to the facility to assess the situation. To get accurate information without putting people or equipment at risk, responders would benefit from better technology to sense radioactive material from afar. That could come from high-power pulsed electromagnetic waves, reports a team from Ulsan National Institute of Science & Technology (UNIST).
First proposed in 2010 by the University of Maryland’s Gregory S. Nusinovich and colleagues, the approach involves using an antenna to direct high-intensity millimeter or terahertz waves at a target area. If material there is radioactive, γ radiation or α particles ionize the surrounding air, releasing free electrons. The interaction of the antenna-directed electromagnetic waves and ionized air induces plasma formation, and the plasma in turn reflects the electromagnetic waves back to the source site for detection.
The UNIST team, led by EunMi Choi, experimentally demonstrated detection of 0.5 µg of cobalt-60 from 120 cm away, the maximum distance allowed by the laboratory setup (Nat. Commun. 2017, DOI: 10.1038/ncomms15394). Off-the-shelf gyrotrons to generate the electromagnetic waves, antennae to direct them, and radiofrequency detectors could be used to deploy the technique for field detection.
Depending on the equipment used, Choi believes the approach could scale to detect radioactivity at distances of at least tens of kilometers and possibly as far as 100 km. Because the time delay of plasma formation depends on γ emission energy, Choi also thinks the technique could be used to identify types of radioactive material.
A University of Maryland (UMD) research team, in collaboration with Monash University and the United States Naval Research Laboratory, has invented a Tunable Large Area Hybrid Metal-Graphene Terahertz Detector, an innovation based upon a successful demonstration of plasmonic resonance in graphene micro-ribbons that are connected to metal electrodes, offering a critical step toward practical graphene terahertz optoelectronic devices.
Graphene, a two-dimensional lattice of pure carbon, is extremely conductive and has unique and advantageous electronic and optical properties that are ideal for a variety of applications, such as sensors, oscillators, electronic components, filters, detectors, and more. Graphene is especially useful in terahertz range, the part of electromagnetic spectrum between microwaves and infrared light, because the free electrons in the material oscillate collectively at these frequencies. The resonance frequency can be tuned by applying an electric voltage at the gate. Being able to tune the resonance frequency allows the resonator to be adjusted, making it usable in a broad range of applications.
“Terahertz technology has a wide variety of potential scientific and commercial applications, ranging from medical diagnosis and screening, manufacturing, security screening, communications, and biochemical sensing,” said Thomas Murphy, Professor of Electrical and Computer Engineering (ECE) and Director of the Institute for Research in Electronics and Applied Physics (IREAP). The invention may offer a dramatic improvement in the ability to increase the speed of short range wireless communication, cutting the amount of time needed to stream a very high quality content between devices. It may offer means ofimprovedsecurity scanning at airports.
Until now, using graphene in terahertz sensors has primarily been theoretical because graphene must touch a metal surface to read out the results or tune the sensor, and this was previously thought to inhibit the plasmonic resonance. But the team invented a new design that does not inhibit charge accumulation at the contact and allows the signal to transfer from the graphene to the metal electrical contacts much more effectively.
The research team includes Murphy; ECE graduate student Mehdi Jadidi; United States Naval Research Laboratory researcher D. Kurt Gaskill; Michael Fuhrer, Research Professor in the Department of Physics and the Center for Nanophysics and advanced-materials/” title=”View all articles about Advanced Materials here”>Advanced Materials and Professor of Physics at Monash University in Australia; Andrei Sushkov, Assistant Research Scientist in the Department of Physics and the Center for Nanophysics and advanced-materials/” title=”View all articles about Advanced Materials here”>Advanced Materials; and H. Dennis Drew, Research Professor in the Department of Physics and the Center for Nanophysics and Advanced Materials.
Electrical connection or antenna coupling to graphene is a problem that has puzzled theresearchers for many years, but the idea behind the team’s discovery originated with Jadidi.
The discovery has the potential to advance the field, and the team is excited to continue their research and further develop the technology in preparation for commercialization.
“We would be thrilled if this invention found near-term commercial applications,” said Murphy. “Perhaps the most promising short-term application would be for room-temperature tunable terahertz detectors.
The invention has been nominated by UMD’s Office of Technology Commercialization for the Invention of the Year award in the Physical Sciences category at the Celebration of Innovation and Partnerships on May 9th as part of the University of Maryland’s “30 Days of EnTERPreneurship.”
Princeton University researchers have built a rice grain-sized laser powered by single electrons tunneling through artificial atoms known as quantum dots. The tiny microwave laser, or "maser," is a demonstration of the fundamental interactions between light and moving electrons.
The researchers built the device—which uses about one-billionth the electric current needed to power a hair dryer—while exploring how to use quantum dots, which are bits of semiconductor material that act like single atoms, as components for quantum computers.
"It is basically as small as you can go with these single-electron devices," said Jason Petta, an associate professor of physics at Princeton who led the study, which was published in the journal Science.
The device demonstrates a major step forward for efforts to build quantum-computing systems out of semiconductor materials, according to co-author and collaborator Jacob Taylor, an adjunct assistant professor at the Joint Quantum Institute, University of Maryland-National Institute of Standards and Technology. "I consider this to be a really important result for our long-term goal, which is entanglement between quantum bits in semiconductor-based devices," Taylor said.
The original aim of the project was not to build a maser, but to explore how to use double quantum dots—which are two quantum dots joined together—as quantum bits, or qubits, the basic units of information in quantum computers.
"The goal was to get the double quantum dots to communicate with each other," said Yinyu Liu, a physics graduate student in Petta's lab. The team also included graduate student Jiri Stehlik and associate research scholar Christopher Eichler in Princeton's Department of Physics, as well as postdoctoral researcher Michael Gullans of the Joint Quantum Institute.
Double quantum dot as imaged by a scanning electron microscope. Current flows one electron at a time through two quantum dots (red circles) that are formed in an indium arsenide nanowire. Credit: Science
Because quantum dots can communicate through the entanglement of light particles, or photons, the researchers designed dots that emit photons when single electrons leap from a higher energy level to a lower energy level to cross the double dot.
Each double quantum dot can only transfer one electron at a time, Petta explained. "It is like a line of people crossing a wide stream by leaping onto a rock so small that it can only hold one person," he said. "They are forced to cross the stream one at a time. These double quantum dots are zero-dimensional as far as the electrons are concerned—they are trapped in all three spatial dimensions."
The researchers fabricated the double quantum dots from extremely thin nanowires (about 50 nanometers, or a billionth of a meter, in diameter) made of asemiconductor materialcalled indium arsenide. They patterned the indium arsenide wires over other even smaller metal wires that act as gate electrodes, which control the energy levels in the dots.
To construct the maser, they placed the two double dots about 6 millimeters apart in a cavity made of a superconducting material, niobium, which requires a temperature near absolute zero, around minus 459 degrees Fahrenheit. "This is the first time that the team at Princeton has demonstrated that there is a connection between two double quantum dots separated by nearly a centimeter, a substantial distance," Taylor said.
When the device was switched on, electrons flowed single-file through each double quantum dot, causing them to emit photons in the microwave region of the spectrum. These photons then bounced off mirrors at each end of the cavity to build into a coherent beam of microwave light.
One advantage of the new maser is that the energy levels inside the dots can be fine-tuned to produce light at other frequencies, which cannot be done with other semiconductor lasers in which the frequency is fixed during manufacturing, Petta said. The larger the energy difference between the two levels, the higher the frequency of light emitted.
Claire Gmachl, who was not involved in the research and is Princeton's Eugene Higgins Professor of Electrical Engineering and a pioneer in the field of semiconductor lasers, said that because lasers, masers and other forms of coherent light sources are used in communications, sensing, medicine and many other aspects of modern life, the study is an important one.
"In this paper the researchers dig down deep into the fundamental interaction between light and the moving electron," Gmachl said. "The double quantum dot allows them full control over the motion of even a single electron, and in return they show how the coherent microwave field is created and amplified. Learning to control these fundamental light-matter interaction processes will help in the future development of light sources."
The random Raman laser is the lastest technology to detect explosives and other nasty stuff from a safe vantage
Being standoffish is usually frowned upon—that is, unless what you’re standing off from might be an explosive or a cloud of anthrax spores. That’s why efforts have accelerated to develop standoff detection techniques that use lasers to identify chemicals and biological substances from a safe distance.
The newest entry in the field is called random Raman spectroscopy. Shine a laser beam into a loose material—say, a powder—and if the density is right, the photons will bounce around among the powder’s particles until they stimulate a new laser emission. Such a random laser, as it is known, works much the same way as a more traditional laser cavity, only without mirrors.
Normally, about 1 in 10 million photons undergoes a process called spontaneous Raman scattering, in which it drops to a lower frequency determined by the particular molecule it’s bouncing off. The random laser enhances this Raman scattering, producing a signal strong enough for a detector to pick up at a distance. By measuring the shift in frequency, scientists can tell the chemical makeup of the powder.
Marlan Scully and Vladislav Yakovlev of Texas A&M University, in College Station, demonstrated such a setup. Scully says they can perform spectroscopic analysis of a material at a distance of a kilometer, and that 10 kilometers should be possible. That would be useful for, say, a drone flying over an area where explosives might be hidden, or an airplane measuring the quality of soil on a farm.
One way around the problem is what he calls terahertz-radiation-enhanced emission of fluorescence, which is designed to detect trace gases emitted by an explosive. He focuses laser beams at two wavelengths on a point in the air, where they interact to create a plasma filament that fluoresces in the ultraviolet. He also emits a terahertz pulse. The T-rays interact with the material being studied to provide the spectroscopic information and then interact with the plasma field to alter its fluorescence. That encodes the spectroscopic information onto the ultraviolet radiation, which is easily picked up by a photodetector. Zhang says the challenge of doing this increases with distance, but he’s already demonstrated detection at 10 meters.
Fow-Sen Choa, a professor of computer science and electrical engineering at the University of Maryland, Baltimore County, uses a quantum cascade laser to do photoacoustic spectroscopy. Heating a material with a modulated laser beam causes it to expand and create a pressure wave, as if it were a tiny audio speaker. Microphones pick up the sound wave and identify the material based on its frequency. “Whether it’s TNT or fertilizer, you can tell pretty easily,” Choa says.
Most of the development of this technique is focused on the accurate detection of the sound and elimination of noise, Choa says. “Distance is not yet the focus,” he says. “The issue is how accurate you will be.”
There’s no ideal distance for how far the detector should stand off, says James Kelly, senior scientist at Pacific Northwest National Laboratory, in Richland, Wash., other than far enough to be safe. The distance, and the most effective technology, really depends on the particular requirements of an application.
Kelly’s team is working on being able to measure a substance at a dosage of 1 milligram per square centimeter on a surface. That’s about what you’d get if someone handling explosives had then touched something and left a fingerprint. The team would like to be able to use an eye-safe system such ashyperspectral imaging to scan vehicles coming to a checkpoint or parking at a stadium, for instance, to see if there are any traces of explosives on them. Because it can be challenging to tease out such a signal from those given off by the paint and other coatings on the surface of a car, researchers at PNNL and other teams are using an eye-safe tunable laser to do reflectance-based hyperspectral imaging, in which multiple images of the surface are taken at different wavelengths under the laser’s illumination. Two substances that might be indistinguishable at one wavelength can look very different at another.
For that application, which could be used by the United States’ Transportation Security Administration or border patrol, a distance of 50 to 100 meters might be desirable, Kelly says. A drone surveying a war area would probably require detection distances in the kilometer range.
For a lot of the techniques being developed, it’s not so much the detection technology itself that’s the bottleneck but the analysis of the signal, Kelly says. Finding trace amounts of explosives does little good at a checkpoint if it takes several minutes of computer processing to identify them.
In the end, no one technology is likely to win out, researchers say. More probably, the one that is used will be the one best suited to a particular need. “There’s a whole gamut of techniques people are looking at,” Kelly says.
Researchers have developed a light detector which could revolutionise chemical sensing and night vision technology.
In the latest issue of the journal Nature Nanotechnology, a team of researchers at Monash University, the University of Maryland in the US and the US Naval Research Laboratory have created a light detector based on graphene, a single sheet of interconnected carbon atoms.
The detector can detect light over an unusually broad range of wavelengths, including terahertz waves, which are between infrared and microwave radiation where sensitive light detection is most difficult.
Professor Michael Fuhrer at Monash says the research could lead to a generation of light detectors which could see below the surface of walls and other objects.
“We have demonstrated light detection from terahertz to near-infrared frequencies, a range about 100 times larger than the visible spectrum,” Professor Fuhrer says.
“Detection of infrared and terahertz light has numerous uses, from chemical analysis to night vision goggles and body scanners used in airport security.”
Current applications for terahertz detection are limited, as they need to be kept extremely cold to maintain sensitivity.
Existing detectors that work at room temperature are bulky, slow and expensive.
Professor Fuhrer says the new detector works at room temperature and is already as sensitive as any existing room-temperature detector technology in the terahertz range but is also more than a million times faster.
The device is easily manufactured and could lead to inexpensive infrared cameras or night-vision goggles.
Top-down view of broadband, ultra-fast graphene detector capable of detecting terahertz frequencies at room temperature. Credit: Thomas Murphy
http://phys.org/news/2014-09-ultra-thin-high-speed-detector-captures-unprecedented.html#jCp New research at the University of Maryland could lead to a generation of light detectors that can see below the surface of bodies, walls, and other objects. Using the special properties of graphene, a two-dimensional form of carbon that is only one atom thick, a prototype detector is able to see an extraordinarily broad band of wavelengths. Included in this range is a band of light wavelengths that have exciting potential applications but are notoriously difficult to detect: terahertz waves, which are invisible to the human eye.
The light we see illuminating everyday objects is actually only a very narrow band of wavelengths and frequencies. Terahertz light waves' long wavelengths and low frequencies fall between microwaves and infrared waves. The light in these terahertz wavelengths can pass through materials that we normally think of as opaque, such as skin, plastics, clothing, and cardboard. It can also be used to identify chemical signatures that are emitted only in the terahertz range.
Few technological applications for terahertz detection are currently realized, however, in part because it is difficult to detect light waves in this range. In order to maintain sensitivity, most detectors need to be kept extremely cold, around 4 Kelvin, or -452 degrees Fahrenheit. Existing detectors that work at room temperature are bulky, slow, and prohibitively expensive.
The new room temperature detector, developed by the University of Maryland team and colleagues at the U.S. Naval Research Lab and Monash University, Australia, gets around these problems by using graphene, a single layer of interconnected carbon atoms. By utilizing the special properties of graphene, the research team has been able to increase the speed and maintain the sensitivity of room temperature wave detection in the terahertz range.
Using a new operating principle called the "hot-electron photothermoelectric effect," the research team created a device that is "as sensitive as any existing room temperature detector in the terahertz range and more than a million times faster," says Michael Fuhrer, professor of physics at the University of Maryland and Monash University, Australia.
Graphene, a sheet of pure carbon only one atom thick, is uniquely suited to use in a terahertz detector because when light is absorbed by the electrons suspended in the honeycomb lattice of the graphene, they do not lose their heat to the lattice but instead retain that energy.
The concept behind the detector is simple, says University of Maryland Physics Professor Dennis Drew. "Light is absorbed by the electrons in graphene, which heat up but don't lose their energy easily. So they remain hot while the carbon atomic lattice remains cold." These heated electrons escape the graphene through electrical leads, much like steam escaping a tea kettle. The prototype uses two electrical leads made of different metals, which conduct electrons at different rates. Because of this conductivity difference, more electrons will escape through one than the other, producing an electrical signal.
This electrical signal detects the presence of terahertz waves beneath the surface of materials that appear opaque to the human eye – or even x-rays. You cannot see through your skin, for example, and an x-ray goes right through the skin to the bone, missing the layers just beneath the skin's surface entirely. Terahertz waves see the in-between. The speed and sensitivity of the room temperature detector presented in this research opens the door to future discoveries in this in-between zone.
More information: "Sensitive Room-Temperature Terahertz Detection via Photothermoelectric Effect in Graphene," Xinghan Cai et al. Nature Nanotechnology, dx.doi.org/10.1038/nnano.2014.182
Ever since the first experimental demonstrations in the microwave and visible ranges [1,2], invisibility cloaks have stimulated progress in the fields of metamaterials and transformation optics. Very recently, Farhat and co-workers [3] suggested that arrays of invisibility cloaks may have interesting electromagnetic properties, and suggested some potential applications in noninvasive probing, sensing and communication. Our team, Vera Smolyaninova and Kurt Ermer from Towson University, and Igor Smolyaninov from the University of Maryland demonstrated the first experimental realization of an invisibility cloak array.
Our experiment is based on the recent demonstration of broadband invisibility cloak, which relies on a curved waveguide mimicking the metamaterial properties necessary for cloaking [4]. Since a gap between a gold-coated spherical lens touching a gold-coated planar glass slide provides a good approximation of the required waveguide shape, such geometry can be easily transformed into a large array of broadband invisibility cloaks using commercially available microlens arrays. This work is reported in the May issue of the New Journal of Physics [5]. In the experiments, conducted at Towson University, very large arrays of roughly 25000 cloaks were used to “hide” approximately 20% of the surface area. This is the first experimental arrangement which lets you study mutual interactions of a very large number of invisibility cloaks.
Unlike the so-called “carpet cloaks” which hide objects on the metallic mirror background, every cloak in our array guides light around the cloaked area. While the former approach is akin to rendering bumps on a carpet invisible by allowing them to blend in with the carpet, classical cloaking concentrates on enabling light to flow around an object. Typically, such classical cloaks [1,2] require sophisticated metamaterial nanofabrication. Each material has its own refractive index, which describes how much light will bend in that particular material and defines how much the speed of light slows down while passing through a material. Natural materials typically have refractive indices greater than one. Refraction occurs as electromagnetic waves bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside.
Kurt Ermer of Towson University
Unlike natural materials, metamaterials are able to produce the index of refraction ranging from very large positive values of the order of 100 to less than zero. In particular, artificial metamaterials needed for cloaking must have the index of refraction, which varies from zero to one. Unfortunately, such artificial metamaterials have very large losses. In our cloak array the precisely tapered shape of the waveguide around each cloak alters the refractive index in the same way as in metamaterials, gradually increasing the index from zero to 1 along the curved surface of each microlens. Since light propagates mainly through the air gap, losses in this design are very low, and the resulting structure is broadband. It works across the whole visible light spectrum.
Theoretical work for the design was led by the University of Maryland, with Towson University leading work to fabricate the device and demonstrate its cloaking properties. The cloaking array device is formed by two gold-coated surfaces, one surface being a commercially available microlens array, and the other a flat glass slide. Individual cloaks in the array were separated by about 30 microns, or roughly the width of a human hair, so that a 5 by 5 millimeter squared microlens array would make approximately 25000 individual invisibility cloaks. Instead of being reflected as normally would happen, the light flows around each cloak and shows up on the other side, like water flowing around an array of stones.
[Click on image to see a higher resolution version]
Building and studying the arrays of invisibility cloaks offers more refined experimental tools to test individual cloak performance. Compared to the characterization of individual cloaks, the angular performance of cloak arrays appears to be more sensitive to cloak imperfections. For example, cloak arrays perform better when light is sent in along the row directions. These findings may be useful in such related areas as acoustic and surface-wave cloaking, as well as in the potential practical applications listed above.
On the other hand, since light is “stopped” near each cloak, and the cloak radius depends on the light wavelength, the cloak array produced in our study may be used in the spectrometer on the chip applications. The “trapped rainbow” effect observed near each cloak [6] may find applications in such fields as biosensing and testing for genetic decease. Stopping light at the cloak boundary leads to considerable enhancement of fluorescence near each cloak in the array [6].
The work was funded by the National Science Foundation.
References [1] “Metamaterial electromagnetic cloak at microwave frequencies”, D. Schurig, J.J. Mock, B.J. Justice, S.A. Cummer, J.B. Pendry, A.F. Starr, D.R. Smith, “Metamaterial electromagnetic cloak at microwave frequencies”, Science 314, 977-980 (2006). Abstract. [2] “Two-dimensional metamaterial structure exhibiting reduced visibility at 500 nm”,I.I. Smolyaninov, Y.J. Hung, and C.C. Davis, Optics Letters 33, 1342-1344 (2008). Abstract. [3] “Understanding the functionality of an array of invisibility cloaks”, M. Farhat, P.-Y. Chen, S. Guenneau, S. Enoch, R. McPhedran,C. Rockstuhl, and F. Lederer, Phys. Rev. B 84 235105 (2011). Abstract. [4] “Anisotropic metamaterials emulated by tapered waveguides: application to electromagnetic cloaking”, I.I. Smolyaninov, V.N. Smolyaninova, A.V. Kildishev, and V.M. Shalaev, Phys. Rev. Letters 103, 213901 (2009). Abstract. 2Physics Article. [5] “Experimental demonstration of a broadband array of invisibility cloaks in the visible frequency range”, V.N. Smolyaninova, I.I. Smolyaninov, and H.K. Ermer, New J. Phys. 14, 053029 (2012). Full Article. [6] “Trapped rainbow techniques for spectroscopy on a chip and fluorescence enhancement” V.N. Smolyaninova, I.I. Smolyaninov, A.V. Kildishev, and V.M. Shalaev, Applied Physics B 106, 577-581 (2012).Abstract. arXiv:1101.336.
Several emerging applications of terahertz radiation, including chemical characterization of materials, communication, medical imaging and security screening, have stimulated intense research to access this region of the electromagnetic spectrum, where availability of sources and detectors is quite limited. In an upcoming issue of Nano Letters, Georgetown University scientists Dr. Mohamed Rinzan and Prof. Paola Barbara and their collaborators at the University of Maryland and Northwestern University report on a new, highly-sensitive detector of terahertz radiation. These detectors can determine the radiation frequency, unlike traditional detectors such as bolometers, and can easily detect femtowatts of power. By using on-chip antennas, the coupling of radiation to the detectors was dramatically increased. The work also shows a new, strikingly counterintuitive effect: exposure to radiation cools the sensors, which further improves their performance; bolometers and many other detectors are heated by exposure to radiation. These results can potentially be applied to graphene and pave the way to practical, highly sensitive terahertz spectral analyzers.
http://www.nanowerk.com/news/newsid=25466.php
(Nanowerk News) Researchers at the Center for Nanophysics and Advanced Materials of the University of Maryland have developed a new type of hot electron bolometer a sensitive detector of infrared light, that can be used in a huge range of applications from detection of chemical and biochemical weapons from a distance and use in security imaging technologies such as airport body scanners, to chemical analysis in the laboratory and studying the structure of the universe through new telescopes.
The UMD researchers, led by Research Associate Jun Yan and Professors Michael Fuhrer and Dennis Drew, developed the bolometer using bilayer graphene--two atomic-thickness sheets of carbon. Due to graphene's unique properties, the bolometer is expected to be sensitive to a very broad range of light energies, ranging from terahertz frequencies or submillimeter waves through the infrared to visible light.
The graphene hot electron bolometer is particularly promising as a fast, sensitive, and low-noise detector of submillimeter waves, which are particularly difficult to detect. Because these photons are emitted by relatively cool interstellar molecules, submillimeter astronomy studies the early stages of formation of stars and galaxies by observing these interstellar clouds of molecules. Sensitive detectors of submillimeter waves are being sought for new observatories that will determine the redshifts and masses of very distant young galaxies and enable studies of dark energy and the development of structure in the universe.
University of Maryland researchers propose method to sniff out dirty bombs via the electromagnetic breakdown of air
Washington, D.C. (November 9, 2010) -- Researchers at the University of Maryland have proposed a scheme for detecting a concealed source of radioactive material without searching containers one by one. Detection of radioactive material concealed in shipping containers is important in the early prevention of "dirty" bomb construction. The concept, described in the Journal of Applied Physics, is based on the gamma-ray emission from the radioactive material that would pass through the shipping container walls and ionize the surrounding air.
The facilitated breakdown of the air in a focused beam of high-power, coherent, terahertz or infrared radiation would then be an indicator of the presence of the radioactive material. The gamma rays coming through the container walls could be detected by a pulsed electromagnetic source of duration between 10 ns to microseconds.
The team evaluated several candidate sources for this detection, including a 670-GHz gyrotron oscillator with 200-kW, 10-µs output pulses and a TEA CO2 laser with 30-MW, 100-ns output pulses. A system based on the 670-GHz gyrotron would have enhanced sensitivity and a range exceeding 10 m.
"It is not yet clear whether this approach to detection of nuclear material is practical," says first author professor Victor Granatstein, "but it is worth pursuing since it might impact an important need related to National Security."
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The article, "Detecting Excess Ionizing Radiation by Electromagnetic Breakdown of Air" by Victor L. Granatstein and Gregory S. Nusinovich appears in the Journal of Applied Physics. See: http://link.aip.org/link/japiau/v108/i6/p063304/s1
