Homeland Security Applications Research Articles

(Invited) Deep Ultraviolet Light Emitting Diodes: Physics, Performance, and Applications

Materials quality is the one of the key factors determining the Deep UV LED performance. It could be dramatically improved by using novel MEMOCVD® technique [1] using overlapping precursor pulses, optimized precursor waveforms and lower growth temperatures compared to the conventional MOCVD growth. Another key factor is the Deep UV LED design. Using very narrow quantum wells (QWs), we achieved an improved overlap between electron and hole wave functions and increased the Internal Quantum Efficiency. We also used “the energy tub” [2] to increase the electron capture into the QWs and eliminate or reduce the “blocking layer.” These approaches and a novel transparent and reflecting top contact have led to a high internal quantum efficiency, high power output and high external quantum efficiency of our Deep UV LEDs. Research is now under way to use these devices for improving quality and extending storage time of fruits and vegetables.[3] Other applications include water and air purification, sterilization, biological threat identification, applications in medicine, biology, industrial processes, defense, and homeland security. Deep UV LEDs have a potential of replacing conventional ultraviolet Hg vapor, Xenon and Deuterium lamps that are bulky, contain mercury, produce ozone, require high voltages, slow to turn on, and have a limited set of available wavelengths. DUV LEDs will also enable new applications that were not even possible with conventional deep UV technology. [1] R. Gaska, J. Zhang, and M. Shur “Nitride-based light emitting heterostructure”, US Patent 7,326,963, Feb. (2008)[2] Q. Fareed, R. Gaska and M. S. Shur, Methods of Growing Nitride-Based Film Using Varying Pulses, US patent 7192849, March 20 (2007)[3] M. Shur and S. Britz, Fluorescent-based ultraviolet illumination, United States Patent Application Publication, US 2011/0147617, June 23 (2011), US patent 8,384,047, Feb. 26 (2013)

(Invited) Deep Ultraviolet Light Emitting Diodes: Physics, Performance, and Applications

The key factor for developing deep UV LEDs is material’s quality of nitride epitaxial films. It could be dramatically improved by using novel MEMOCVD® technique. Using very narrow quantum wells (QWs) and energy band gap engineering in deep UV LEDs improves overlap between electron and hole wave functions and increases the Internal Quantum Efficiency (IQE) and External Quantum Efficiency (EQE). A novel transparent and reflecting top contact further boosts IQE and EQE and increases the power output and high external quantum efficiency of our Deep UV LEDs. Research is now under way to use these devices for improving quality and extending storage time of fruits and vegetables. Other applications include water and air purification, sterilization, biological threat identification, applications in medicine, biology, industrial processes, defense, and homeland security.

Response of Inorganic Scintillators to Neutrons of 3 and 15 MeV Energy

In the perspective of the development of future high energy physics experiments, homogeneous calorimeters based on inorganic scintillators can be considered for the detection of hadrons (e.g., calorimeter based on dual-readout technique). Although of high importance in the high energy physics framework as well as for homeland security applications, the response of these inorganic scintillators to neutrons has been only scarcely investigated. This paper presents results obtained using five common scintillating crystals (of size around 2×2×2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), namely lead tungstate (PbWO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ), bismuth germanate (BGO), cerium fluoride (CeF ), Ce-doped lutetium-yttrium orthosilicate (LYSO:Ce) and lutetium aluminum garnet (LuAG:Ce) in a pulsed flux of almost mono-energetic (~3 MeV and ~15 MeV) neutrons provided by the Van de Graff accelerator SAMES of CEA Valduc. Energy spectra have been recorded, calibrated and compared with Geant4 simulations computed with different physics models. The neutron detection efficiency for these crystals has been estimated and compared with simulation.

Mechanics and Energetics of DNA Hybridization on Single-Walled Carbon Nanotubes Explored Using Adaptive Biasing Force Calculations

Hybrid nanostructures consisting of single-walled carbon nanotubes (swCNs) coated with single stranded DNA (ssDNA) are of great interest due to their numerous potential applications in nanotechnology, medicine, and homeland security. Recent experiments have demonstrated that DNA-CN hybrids can detect the hybridization of complementary DNA strands, paving the way for applications in DNA sequencing and genetic testing. However, the molecular mechanisms remain poorly understood. Previous molecular dynamics (MD) simulations studying DNA-CN self-assembly have found that adsorbed DNA bases are poorly positioned to hybridize with complementary DNA strands. Here, we apply the adaptive biasing force (ABF) method to all-atom MD models, and find that DNA bases must desorb from the swCN sidewall and suffer significant energy penalties to hybridize with complementary DNA. This agrees with the extremely slow hybridization time scales in fluorescence experiments, as well as observations made using DNA-CN transistor devices. We present the free energy landscape for two model systems and compare the energy required to hybridize a G-C versus an A-T pair. These results reveal significant impediments to rapid DNA hybridization on the swCN surface, and further our understanding of the mechanism by which hybridization gradually occurs—essential knowledge for the advancement of nanotechnology based on DNA-CN.

A LABORATORY-BASED X-RAY PHASE CONTRAST IMAGING SCANNER WITH APPLICATIONS IN BIOMEDICAL AND NON-MEDICAL DISCIPLINES

X-ray phase contrast imaging (XPCi) provides a much higher visibility of low-absorbing details than conventional, attenuation-based radiography. This is due to the fact that image contrast is determined by the unit decrement of the real part of the complex refractive index of an object rather than by its imaginary part (the absorption coefficient), which can be up to 1000 times larger for energies in the X-ray regime. This finds applications in many areas, including medicine, biology, material testing, and homeland security. Until lately, XPCi has been restricted to synchrotron facilities due to its demanding coherence requirements on the radiation source. However, edge illumination XPCi, first developed by one of the authors at the ELETTRA Synchrotron in Italy, substantially relaxes these requirements and therefore provides options to overcome this problem. Our group has built a prototype scanner that adapts the edge-illumination concept to standard laboratory conditions and extends it to large fields of view. This is based on X-ray sources and detectors available off the shelf, and its use has led to impressive results in mammography, cartilage imaging, testing of composite materials and security inspection. This article presents the method and the scanner prototype, and reviews its applications in selected biomedical and non-medical disciplines.

Pressure-Sensitive Sampling Wands for Homeland Security Applications

This paper discusses the use of force sensing resistor (FSR) technology integrated into sampling wands used for homeland security applications. FSR-integrated wands can be used for the optimization of wipe sampling of surfaces to facilitate enhanced trace contraband collection. Collection efficiencies during wipe sampling are known to be dependent on the applied force, or pressure, used during sampling. Light-emitting diodes designed to switch from red to green at a defined force threshold of 7 N provide feedback to the operator during sampling. The goal of maintaining forces at or above the threshold was successfully demonstrated by testing with a volunteer population of 22. An additional benefit is the reduction in the variability of the force applied by each operator during sampling. Another focus area is the development of prototype sampling wands that fit in the palm of the hand and other wand modifications that increase the reliability of wipe sampling by registering the placement of the collected sample properly on the wipe. This paper also outlines how an array-based FSR can be used to visualize contact area and pressure during wipe sampling.

Lasing spaser in two-dimensional plasmonic crystals

The laser is arguably the most important and versatile optical device. Invented just over 50 years ago,1 the laser has found immense number of uses from fundamental science and ultra-precision metrology to diverse applications in telecommunications, entertainment, computers, displays, biomedicine, materials processing, defense and homeland security and so on. These are based on fundamental property of the laser to generate coherent light that can be focused to microscopic areas or concentrated in pulses as short as 100 as (1 as =10−18 s). Still, quest for new lasers continues, in particular, to design the smallest and thinnest lasers possible. This is important in many respects, in particular, because such lasers can be directly modulated with a very high frequency. One way to achieve this goal is provided by invention of the spaser (Surface Plasmon Amplification Stimulated Emission of Radiation),2 also called plasmonic laser, about 10 years ago. Replacing light quanta—photons—of the laser with electronic excitations at the surface of metals called surface plasmons, which can have atomic-scale dimensions, the spaser itself can be as small or as thin as the dimension of only hundreds of atoms.

Improving Consistency in the Radiation Fields Used During Testing of Radiation Detection Instruments for Homeland Security Application

Improving Consistency in the Radiation Fields Used During Testing of Radiation Detection Instruments for Homeland Security Application

Experimental tests of the new plastic scintillator with pulse shape discrimination capabilities EJ-299-33

We have studied the prototype of a new plastic scintillator material (EJ-299-33) engineered for gamma-neutron discrimination. Energy and time resolutions as well as pulse shape discrimination capability have been compared with those of standard plastic and liquid scintillators. EJ-299-33 characteristics are somewhat poorer compared to standard scintillators. However, results obtained with the new plastic material suggest its possible use in basic research (time-of-flight measurements) as well as in Homeland Security applications (neutron/gamma monitoring device).

Non-Electric Applications of the Inertial Electrostatic Confinement Fusion Concept

Electrical energy is not the only commercial product that can be produced by the fusion of light elements. The reaction products from many fusion fuels can be used to provide products that can be of a near-term benefit to society well before practical fusion power plants are a reality. The use of fusion products (neutrons and protons) in Homeland Security applications to detect clandestine materials or the production of short half life Positron Emission Tomography isotopes for medical diagnostics of abnormalities (e.g. cancers) in the human body are but a few of the near term examples of the near term use of fusion energy. This paper shows how one of the many ways to promote fusion, namely the use of the Inertial Electrostatic Confinement concept, is uniquely suited to this task worldwide.

CaF2(Eu): an ``old'' scintillator revisited

Homeland security applications demand performant two-plane Compton-camera systems, with high detector efficiency, good nuclide identification and able to perform in-field conditions. A low-Z scintillator has been proposed and studied as a promising candidate for use in the scattering plane of a scintillator-based Compton camera: CaF2(Eu) [1]. All the relevant properties for the application of this scintillator in a mobile Compton camera system, have been addressed: the energy resolution and the non-proportionality at room temperature and in the temperature range of -20°C to +55°C, the photoelectron yield and the relative light yield in the relevant temperature range. A new method of inferring the relative light output of scintillators has been proposed.

A simulation study of ad hoc networking of UAVs with opportunistic resource utilization networks

Specialized ad hoc networks of unmanned aerial vehicles (UAVs) have been playing increasingly important roles in applications for homeland defense and security. Common resource virtualization techniques are mainly designed for stable networks; they fall short in providing optimal performance in more dynamic networks—such as mobile ad hoc networks (MANETs)—due to their highly dynamic and unstable nature. We propose application of Opportunistic Resource Utilization Networks (Oppnets), a novel type of MANETs, for UAV ad hoc networking. Oppnets provide middleware to facilitate building flexible and adaptive distributed systems that provide all kinds of resources or services to the requesting application via a helper mechanism. We simulated a homeland defense use case for Oppnets that involves detecting a suspicious watercraft. Our simulation compares performance of an Oppnet with a baseline case in which no Oppnet is used. The simulation results show that Oppnets are a promising framework for high-performance ad hoc UAV networking. They provide excellent performance even under imperfect (and realistic) conditions, such as a less invasive use of helpers, denial of help by some of the candidate helpers, and imperfect detection capabilities of Oppnet components.

Applications of switching reagent ions in proton transfer reaction mass spectrometric instruments for the improved selectivity of explosive compounds

Here we demonstrate the use of a switchable reagent ion proton transfer reaction mass spectrometry (SRI-PTR-MS) instrument to improve the instrument's selectivity for the detection of the explosive compounds 2,4,6 trinitrotoluene (TNT), 1,3,5 trinitrobenzene (TNB), pentaerythritol tetranitrate (PETN), and cyclotrimethylenetrinitramine (RDX). Selectivity is improved owing to the production of different product ions resulting from changes in the reagent ion-molecule chemistry. To be of use as an analytical tool for homeland security applications, it is important that the reagent ions (and hence product ions) can be rapidly changed (within seconds) from H3O+ to another dominant ion species if the technology is to be acceptable. This paper presents measurements that show how it is possible to rapidly switch the reagent ion from H3O+ to either O2+ or NO+ to enhance selectivity for the detection of the four explosives named above. That switching reagent ions can be done quickly results from the fact that the recombination energies of O2+ and NO+ are less than the ionisation potential of H2O, i.e. charge transfer cannot occur which otherwise would result in ions that can react efficiently with water (e.g. H2O++H2O→H3O++OH) leading to H3O+ becoming the dominant reagent ion. Reaction processes observed are non-dissociative charge transfer (O2+ with TNT and TNB), dissociative charge transfer (O2+ with TNT) and adduct formation (NO+ with PETN and RDX). O2+ is found to be unreactive with PETN and RDX, and under the conditions operating in the reaction region of the PTR-MS only a low signal associated with NO+·TNT was observed. No NO+·TNB was detected.

Recommendations for Improving Consistency in the Radiation Fields Used During Testing of Radiation Detection Instruments for Homeland Security Applications.

Several measurements and calculations were performed to illustrate the differences that can be observed in the determination of exposure rate or ambient dose equivalent rate used for testing radiation detection systems against consensus standards. The large variations observed support our recommendation that better consistency in the test radiation fields can be achieved by specifying the source activity and testing distance instead of the field strength.

GEM APPLICATIONS OUTSIDE HIGH ENERGY PHYSICS

From its invention in 1997, the Gas Electron Multiplier (GEM) has been applied in nuclear and high energy physics experiments. Over time however, other applications have also exploited the favorable properties of GEMs. The use of GEMs in these applications will be explained in principle and practice. This paper reviews applications in research, beam instrumentation and homeland security. The detectors described measure neutral radiations such as photons, x-rays, gamma rays and neutrons, as well as all kinds of charged radiation. This paper provides an overview of the still expanding range of possibilities of this versatile detector concept.

The Evolution of Neutron Straw Detector Applications in Homeland Security

The dwindling supply of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He has necessitated the adoption of new technologies for detection of neutrons especially in Homeland Security (HS), where detectors require large volumes of the precious gas. The boron-coated straw (BCS) technology consists of very thin-walled metal tubes equipped with a highly robust coating of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> C on the inner wall. The coating, applied with Physical Vapor Deposition (PVD), is atomically bound to the metal substrate, and it is able to resist delamination over a temperature range from -200 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C to 1000 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. Accelerated lifetime testing of sealed straw detectors over extreme temperature ranges (-70 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C to +125 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C) have recently demonstrated a 99% expected lifetime of 30 years. At the same time, the coating purity is high, with a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B content approaching 77%. Straws stacked 5 deep in a dense array have demonstrated an efficiency of > 70% when evaluated in a cold neutron beam. A number of field worthy HS detectors have been developed over the past 2 years based on the BCS. Examples are presented, including neutron modules for Radiation Portal Monitors (RPM), a vehicle mounted modular detector with an intrinsic efficiency of 30% for unmoderated <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">252</sup> Cf neutrons, and handheld detectors. All of these systems have been government tested. The <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> C coated straw offers a highly versatile, robust and low cost technology meeting multiple needs in homeland and international security.

Boron-Coated Straw Detectors for Backpack Monitors

The limited inventory and minute natural abundance of 3He gas on Earth necessitate the adoption of new technologies for the detection of neutrons, especially in homeland security applications, where large volume deployments are required. We investigate the neutron detection efficiency of a backpack radiation detector based on an unmoderated array of boron-coated straws (BCS). A neutron module was configured that would be light and small enough to fit inside a regular-sized backpack. The module consisted of 36 tubes, arranged in two rows, for a total number of BCS detectors equal to 36 × 7=252. The overall dimensions of the neutron module were 3.18 cm × 26.7 cm × 38.1 cm, and its weight was 1.62 kg (3.57 lbs). The module was fitted immediately inside the back side of the backpack. The detectors are thus very close to the torso of the operator, which, together with a plastic scintillator for gamma detection, act as moderators for high-energy neutrons. In order to maintain a low weight, no other moderating material was installed inside the backpack. The weight of the pack containing both neutron and gamma detector panels, along with foam packing, electronics, and battery, was 5.36 kg (11.8 lbs). The compact dimensions of the design afforded use of a computer style backpack of minimal dimension providing significant additional operational advantages. The testing results indicate that, through use of high-density straw cluster detectors, the proposed design meets both neutron and gamma response government requirements for backpack monitors.

Characterization of the Photoneutron Flux Emitted by an Electron Accelerator Using an Activation Detector

Electron accelerators are intense photoneutron sources for nuclear waste packages characterization and homeland security applications. Moreover, when considering medical accelerators, photoneutrons can cause secondary cancers for patients and also expose hospital staff to deactivation gammas after the irradiation. In this study, we investigate photoneutrons properties according to average emission intensity, energy spectrum and spatial distribution. The latter parameter was measured using an activation detector and the other two parameters were determined by simulation, and then, evaluated by comparing absolute activation simulations and measurements. Our methodology was applied to characterize the photoneutron flux generated by two electron accelerators. Our study has shown that there is a strong probability for photonuclear cross-sections to be undervalued in the energy range studied.

A multi-energy X-ray backscatter system for explosives detection

Most luggage inspection systems are based on X-ray transmission technologies, such as radiography and computed tomography. These techniques have limitations, especially with large or dense objects or objects which are placed close to a wall not allowing access to the rear side for radiography (for instance with abandoned luggage). Portable systems using backscattered X-rays could be an alternative solution when analyzing a suspicious object from one side only, without contact, particularly for homeland security applications. However, portable systems are not currently available. X-ray backscatter imaging, unlike X-ray radiography, reveals low Z materials such as explosives, which may be hidden inside luggage or behind a screen. Specific analysis of backscattered spectra can provide further information about the suspect material in the backscatter image. This can help discriminate between explosive and inert materials. In this article, we detail this discrimination process and the associated developed laboratory prototype. Experimental results are presented, demonstrating the system's performance.

Routine Surveys for Gamma-Ray Background Characterization

In gamma-ray spectroscopy and imaging, the natural gamma-ray background can significantly reduce detection sensitivity, especially when the source is weak and the background varies substantially. This project aims to systematically measure and characterize the spatial and temporal variations of the background in order to assess their impact on detection sensitivity and specificity for homeland security applications. An extensive survey of typical backgrounds found in the San Francisco bay area was performed, and initial measurement results are presented here.