No hiding place for landmines

Scientists from the US Department of Energy’s Pacific Northwest National Laboratory believe they have developed a landmine detector that will greatly assist in the challenge of clearing the existing inventory of 110 million landmines that are buried throughout 70 countries in the world.

Called the Timed Neutron Detector, the prototype offers benefits such as low price, quick assessment, ease of use and the ability to detect mines containing little or no metal.

The Timed Neutron Detector appears similar to a metal detector yet applies physics to discover signs indicative of a landmine’s presence. Specifically, the system detects hydrogen, which is present in casings and explosives found in plastic or metal landmines, and its interactions with neutrons.

The PNNL-developed system consists of a small neutron source and a detector built into one system that a person sweeps over the ground in the same manner as a metal detector.

PNNL physicists designed the neutron source to hold a small amount of californium-252 which, during natural decay, emits up to four neutrons.

Electronics built into the neutron source record the time fission occurred. This process, called time tagging, allows the system to differentiate between neutrons that have interacted with hydrogen in landmines and those that are scattered from the soil. If the neutrons encounter a buried landmine — plastic or metal — they will interact with any hydrogen found in the casing or explosive material.

During this interaction, hydrogen removes part of the neutron’s energy and reflects those neutrons back toward the handheld system.

Slow neutrons return to the detector. Once inside, nonradioactive helium-3 stored in low-pressure pipes collects a neutron then emits an electron.

A tube with high-voltage wire collects those electrons and translates them into a simple determination of whether a landmine exists.

PNNL physicists are said to have chosen to target hydrogen because it removes more energy from neutrons than other elements, making the change in energy of neutrons easier to identify. Hydrogen is also a common element in both metal and plastic mines.

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