Minding mines—new landmine detection device developed

To safely deal with the 110 million landmines hidden in the soil of nearly 70 countries, two separate but equally challenging tasks must be completed. Before mines can be removed and disarmed, they must first be found.

Researchers at Pacific Northwest National Laboratory are building a portable system to detect landmines that is especially useful in locating those most difficult to spot—landmines that contain little or no metal.

With more than 40 years' experience in radiation detection and arms control treaty verification, Pacific Northwest scientists put physics to work in their prototype detection device, the Timed Neutron Detector.

The system looks like a portable metal detector and is swept over the ground in much the same way. It sends neutrons into the soil and detects whether they interact with hydrogen, which is present in casings and explosive material found in both plastic and metal landmines.

"The system is lightweight, affordable and can scan large areas," said Richard Craig of the engineering physics group, who led development efforts. "We focused on these characteristics so that the system would be more likely to be used in Third World countries that have the greatest need for clearing mines."

One key component of the Timed Neutron Detector is a neutron source about the size of a personal pager that is designed to hold a small amount of californium-252. Fission events during this isotope's natural decay process cause three or four neutrons to shoot from the source. Electronics built into the system record the time when fission occurs and the neutrons leave the source at speeds thousands of times faster than a bullet shot from a rifle.

If these neutrons travel through the soil and encounter a landmine, they will interact with the hydrogen in the casing or explosives. The hydrogen will remove a portion of the neutron's energy and reflect what are called "slow neutrons" back toward the handheld device. Neutrons simply scattered by the dirt are not slowed in the same way.

The second major component of the system—the detector—determines if a slow neutron returns to the system. Nonradioactive helium-3 stored in low-pressure metal tubes collects the neutron and in turn, emits an electron. The electrons are collected in the tube where high-voltage wires carry their energy and signal that a landmine exists in that area.

This technology was field tested on simulated mines and was presented as part of the international meeting of the American Nuclear Society and European Nuclear Society in Washington, D.C. in late 2000. Pacific Northwest is seeking outside funds for continued development activities and intends to commercialize the technology.