Dangerous times call for high-tech answers. Today's detection and neutralization systems help guard our borders against people, cargo, and vehicles that may be carrying explosives, arms, and contraband that could include pathogenic and even nuclear material. All these perils make for a lucrative industry, as analysts say the homeland security market could total tens of billions of dollars. Just look at the technologies in the mix: X-ray, ultrasonic, neutron-bombardment, gravity gradient, optical, infrared (IR), and terahertz (THz) imaging, as well as RFID technology.
X-Ray Marks The Spot
A number of recent advances have fortified conventional security methods. Widely used in airports, government buildings, courthouses, and correctional facilities, fixed-location and limited-mobility X-ray systems are now giving way to portable, lower-cost, back-scatter X-ray imagers that can be set up anywhere. Back-scatter X-ray imaging reveals details missed by traditional transmission X-ray imaging.
For example, American Science and Engineering developed the Gemini dual-energy X-ray imaging technique, which allows for the simultaneous detection of previously undetectable organic and inorganic items under inspection (Fig. 1).
Gemini's Z-Backscatter system features enhanced detection of organic-materials—like sheet and bulk explosives, narcotics, and plastic weapons—frequently missed with conventional transmission X-ray systems. The system colorizes the objects it scans by determining the material type (the atomic number) of any object being scanned, generating a clear uncluttered display.
X-ray photons scatter differently when they encounter varied types of materials. Take Compton scattering, which is material-dependent. Materials with lower atomic numbers scatter more strongly than materials with higher numbers. Elements with higher atomic numbers are more likely to absorb X-rays, either before or after being scattered.
X-ray imaging can be augmented with neutron-based systems to detect "dirty bombs." Experts at the Institute Ruder Boskovic, Zagreb, Croatia, are proposing such a system. Here, X-rays can be used to conduct a fast initial check to identify a "suspect" region and then provide the region's coordinates to the neutron-based system for final confirmation. The system would use a 14-MeV neutron beam defined by the detection of the associated alpha particles. Tests have shown that such a system can accurately distinguish between depleted uranium, lead, and iron.
Active neutron activation, a technique developed at the Lawrence Livermore National Laboratory (LLNL), is considered a major breakthrough in cargo inspection. The method's lower energy levels (3.7 MeV versus 14 MeV) eliminate the nitrogen interference due to oxygen activation found in conventional inspection techniques (Fig. 2).
Another promising LLNL technique is pulsed fast-neutron analysis for element-and metal-specific imaging. It consists of a neutron source, gamma detectors, signal-processing systems, and an operator display (Fig. 3). And, LLNL is investigating other techniques for cargo inspection, besides neutron-based systems.
One interesting concept is based on gravity gradiometry, a passive technique that shielding can't defeat. It positively detects fissile material in most simulations, and it's recommended as a complement to other techniques such as photon or neutron detection. LLNL researchers modeled such a system to resolve a 15-cm3 plutonium pit surrounded by lead shielding.
Neutron-based systems aren't the sole purview of the U.S. The European Union is developing the EURITRACK (EUropean Illicit TRafficking Countermeasures Kit) tagged-neutron project to inspect cargo containers. It's part of the EU's 6th Framework Program.
The Tagged Neutron Inspection System (TNIS) features a transportable deuterium-tritium neutron generator, position-sensitive alpha detectors, fast-neutron and gamma-ray detectors, and data-acquisition and analysis circuitry (Fig. 4). System components will be integrated this year at Croatia's Zagreb Ruder Boskovic Institute.The entire system will be demonstrated next year in France.
Nevada Nanotech Systems believes that the ultimate problem in the trace detection of chemicals, biological agents, and explosives hidden in cargo is sampling. This methodology means more sensors are needed in more places to successfully tackle the sampling challenge.
As a result, the company opted to develop a self-sensing array (SSA) based on micro-cantilevers to detect chemicals, biological agents, and explosives. Nevada Nanotech Systems believes that this technology can be realized in a device that measures just two cubic centimeters, runs on a watch battery, and costs only a few hundred dollars.
Nevada Nanotech Systems successfully tested the system against seven chemical agents, including toxic industrial chemicals like ammonium hydroxide, toluene diisocyanate, formaldehyde, and allyl alcohol. The SSA also detected serratia marcescens, a biological agent analog to the plague, among other bacteria using a new technique. And, the system detected explosives vapors from trinitrotolune (TNT), pentaerythritol tetranitrate (PETN), and cyclotrimethylene trinitramine (RDX).
Ultrasound is one of many technologies being employed in detecting illegal materials in cargo shipments. Researchers at the Pacific Northwest National Laboratory (PNNL) came up with a prototype portable handheld hazardous-materials acoustic inspection device. It non-invasively interrogates and identifies fluids in sealed containers by using ultrasonic velocity and attenuation measurements. PNNL believes such a system would be invaluable in homeland-security applications.
Another potentially important technology is optical frequency combs. Researchers at the National Institute of Standards and Technology (NIST) demonstrated a novel system based on these combs, which can detect a wide variety of molecules in tiny trace amounts at high speed. Possible applications include explosive detection at airports, chemical analysis in labs, and pathogen detection for homeland security and healthcare. NIST conducted these experiments jointly with the University of Colorado at Boulder.
IR thermal imaging, particularly the development of lower-cost uncooled IR imagers, is another rapid-growth technology. Analysts estimate that the market for IR imaging and night-vision cameras and systems adds up to as much as $2 billion. These imagers also are referred to as microbolometers.
The cost for uncooled IR thermal-imaging arrays runs about half the price of conventional cooled imagers. Also, they're smaller and feature quieter operation. However, this comes at the expense of lower sensitivity, slower response time, and the need for optics to achieve longerrange performance. Cooled mid-wavelength IR imagers could mitigate some of these drawbacks.
Novel manufacturing methods like that used by Electro-optic System Design promises the volume production of silicon MOEMS (micro-optical electromechanical systems) passive IR sensors for $100 to $500. The mosaic-pixel, focal-plane-array (FPA) design contains a number of individual microbolometer detectors that are electrically interconnected to form an imaging pixel.
Two versions were successfully produced and tested. A small-format large-pixel short-range FPA (up to 25 m) was designed for hot-spot detection in the early stages of a fire. A longer-range version (up 100 m) targets security applications.
RedShift Systems, a pioneer in low-cost thermal-imager development, now supplies its Thermal Light Valve to OEMs for use by first responders, firefighters, and law-enforcement officers, as well as in automobiles. Meanwhile, Lucent Technologies Bell Labs and Isonics Corp. entered into a three-year cross-licensing agreement to produce MEMS IR sensors for defense and homeland-security applications. The agreement contemplates a proof of concept demonstration by the end of this year, followed by commercialization.