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BNL Researchers Work to Develop a Field-Deployable Instrument to Identify Live Ordnance Using Neutrons

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What do sheep in New Zealand have in common with unexploded ammunition on U.S. military firing ranges? They have both been the target of Brookhaven National Laboratory (BNL) Environmental Research and Technology Division scientist Sudeep Mitra’s research into technology using neutron time-of-flight to determine the composition of various materials.

Under its Strategic Environmental Research and Development Program, the Department of Defense (DOD) recently awarded a three-year grant to Mitra and his colleagues at BNL and Stony Brook University to develop a field-deployable instrument that will help identify unexploded ordnance (UXO) at its more than 1,600 U.S. firing ranges without detonating the explosives. The instrument would use the Associated Particle neutron Time-Of-Flight technique (APnTOF) to measure ratios of carbon, nitrogen and oxygen in objects left on the firing ranges.

Mitra used this technology 20 years ago to help ranchers in New Zealand track the progress of genetic manipulations to breed sheep with more meat and less fat without slaughtering the animals.

One of the major problems facing the DOD is unearthed UXO at military facilities. Conventional ground-penetrating radar techniques and magnetometers identify metal objects but do not determine whether they are a dangerous UXO or a benign rusty pipe. The APnTOF technique can be used to examine the object in situ without disturbing it and, based on its chemical composition and ratio of specific elements, determine whether it is a dangerous UXO.

"At the firing ranges where the U.S. military trains, they fire many different kinds of ammunition," Mitra said. "Ten percent of them don’t explode as expected, and although they have color codes for different ammunition, they quickly rust and the color codes disappear.

"When they are practicing, quite often they don’t use high explosives in the fillers of these rockets or bullets," he said. "They could be filled with water or even sand. But you don’t know if it’s high explosive or if it’s just a practice round. So if it is suspicious, they have to call in the technicians, and they blow it up in place at a cost of $600 for each piece."

Since handling every piece of ordnance as "live" greatly increases disposal and remediation costs to the DOD, improvements are needed in the technologies for identification and discrimination of UXO to reduce false alarms.

Carbon, nitrogen and oxygen are the main elements present in high explosives, as well as in sheep and other common objects like newspapers. Mitra’s technique uses an electronically collimated tagged neutron beam from a novel compact, portable field-deployable 14.1 MeV neutron-generator system to simultaneously provide 3D imaging of objects and their elemental composition.

"The system is a mini-accelerator that produces neutrons. With each neutron, there is an associated alpha particle given off in exactly the opposite direction. So the trick here is to have a built-in alpha particle detector. This is the innovation of the system. The moment an alpha particle is detected, I know the neutron is firing in the opposite direction so that means I can tag the neutron.

"That neutron will take a certain time to reach the object in question, since these velocities are very well known. So the distance to the object can be determined with time-of-flight spectra, and signals which are uniquely characteristic of particular elements in varying ratios provide information on the composition of the object. For example, if an object is suspected to be a high explosive, its location can be pinpointed using the time spectrum, and the ratio of corresponding gamma rays and spectrum patterns can determine what it contains."

The technology’s main advantage over its predecessor technique is its suppression of the unrelated background signal by imposing conditions on the data-acquisition system.

"We will undertake experiments to demonstrate the APnTOF’s efficacy under various field conditions for both characterizing munitions types from their elemental composition, and also discriminating hazardous UXO from nonhazardous items among the clutter," he said. "Finally, a portable version will be developed and tested in the field."

The collaboration among different directorates and Stony Brook University brings together a unique combination of expertise. Mitra, the project Principal Investigator, works in the Environmental Sciences Department of the Environmental and Life Sciences Directorate. Istvan Dioszegi, of BNL’s Nonproliferation and National Security Department in the Global and Regional Solutions Directorate, uses techniques to detect neutrons, while Yu Zhou. an assistant professor of robotics at Stony Brook, will develop decision-making algorithms for UXO identification using the gamma ray spectra of different materials. BNL’s Instrumentation Division and microelectronics group will develop the compact field-deployable signal processing system.

Mitra said the system can be easily modified for applications in homeland security, nonproliferation, and carbon sequestration. Another potential application could be for early diagnosis of breast cancer.

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