Oct. 19, 1999 ALBUQUERQUE, NM -- A portable chemical sensor system the size of a soccer ball being developed by scientists at the Department of Energy's Sandia National Laboratories, promises a new way of detecting and identifying even the smallest traces of explosives under water, whether in a rice paddy or deep in the ocean.
The chemical sensor system consists of separate components that take a sample of liquid drawn from water surrounding submerged objects containing explosives, extract the molecules of interest on a fiber, desorb the molecules from the fiber into an Ion Mobility Spectrometer (IMS) and identify the explosive based on chemical signatures of the material.
"This system will fill a unique niche," says Ron Woodfin, project manager. "Unlike the commonly used anomaly detectors, such as metal detectors or ground-penetrating radar, the IMS analyzes the material's actual molecular makeup to identify the explosive type. Its best role is not as a search device, but as a classifier or identifier."
At the heart of the system is a concentration technology that gathers samples on a fiber and concentrates it thousands of times, making the levels large enough to analyze.
Ron assembled a team with Phil Rodacy serving as the technical lead to develop the sensor system. They miniaturized the IMS, reducing it from a commercially made 30-pound shoebox size device to a five-pound unit that fits in a person's hand. When complete, the entire sensor system, including the IMS, concentrator, computer, display and batteries will weigh no more than 20 pounds and be the size of a soccer ball. The small size will make it practical and affordable, the team says.
Through a series of experiments performed at the US Navy facility at San Clemente Island off the coast of San Diego in 1996-98, another in the waters near Panama City, Fla., last year and most recently this August and September in Halifax, Nova Scotia, the researchers showed that the detection system works. Samples of water close to known sites with explosives were successfully collected, concentrated and analyzed.
"Now that we have proved that the technology works we need to get it even smaller and able to function under water," Woodfin says.
The system relies on several factors. First is the phenomenon that all ammunitions or unexploded ordnance items that contain explosives emit molecules of explosive chemicals. If they are submerged in water, the molecules can be found downstream from the explosives. If they are buried in soil, traces can be located in nearby dirt.
The second factor that contributes to the successful sensor system is that a certain type of polymer fiber (polydimethysiloxane/divinylbenzene copolymer) attracts specific types of explosive molecules in cool temperatures.
The third is that the molecules lose their attraction to the fiber when it is heated slightly, causing them to rapidly desorb.
Taking all this into account, the researchers developed a method whereby they insert the polymer fiber into a syringe used to collect water samples near underwater explosive devices. The near-dry fiber containing the molecules is then removed from the collecting device and placed in the IMS where it is heated slightly. The molecules jump off the fiber. By measuring the rate at which the molecules transit the IMS, the researchers determine the identity of the explosive or if the molecules are something else.
To date the chemical sensor system can only work outside water, but the researchers are developing a new waterproof packaging so that it will function under water.
The sensor system has successfully analyzed soil field samples in the laboratory at Sandia's Explosive Components Facility, but, Woodfin says, it is much more effective on samples that have the explosives dissolved in water, and that's why they are now concentrating on that area of research.
Currently, the predominant way of seeking out explosives both on the ground and in water is by using anomaly detectors that identify objects not expected in the environment. A common one is the metal detector, which locates anything with metal, most of which are not ordnance.
"The IMS system exploits a different principle," Rodacy says. "It looks for actual explosive materials, which eliminates the number of false alarms. Either it's an explosive or it's not."
Initial tests of the sensor system were done in 1996 through 1998 at San Clemente Island. The researchers prepared simulated explosive devices using oil drums doped with trace amounts of explosives, submerged them and sent divers in to collect water neat the test area. They were able to detect concentrations of the explosives at distances of more than 40 feet from the source. These initial tests were where the concentration concept was developed.
In a test last year near Panama City, Fla., the researchers submerged actual military hardware containing explosives and collected water near the site. Once again the system was successful in identifying explosive material.
Most recently in August and September, the researchers went to Halifax, Nova Scotia, where they tested waters in the Bedford Basin near two ammunition-laden ships, the Claire Lilly and the Trongate, that sunk in World War II. From the watery graves of these two ships the researchers obtained samples and used the portable chemical sensor system to determine that traces of explosives existed, primarily TNT, cordite, and other materials used 50 years ago. This was verified by further laboratory tests using different analytical techniques.
The earlier San Clemente and Panama City tests were sponsored by Sandia, the Office of Naval Research and the Department of Defense, Office of Munitions. The Nova Scotia venture was sponsored by the Office of Naval Research and hosted by the Defence Research Establishment Atlantic (part of the Canadian Department of National Defence) with help from the Canadian Fleet Diving Unit.
Rodacy anticipates that as the sensor research matures, the technology will rapidly move from the prototype stage to the development stage.
"As we further develop this process, this IMS-based sensor has potential to rapidly and accurately classify explosive ordnance items, doing underwater what demining dogs [canines that sniff out explosives] do today on land, only using electronic and chemical technology," Rodacy says.
Sandia is a multiprogram DOE laboratory, operated by a subsidiary of Lockheed Martin Corp. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major research and development responsibilities in national security, energy and environmental technologies, and economic competitiveness.
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