Seeing the unseen
What about seeing through walls? To help with homeland security, Ka-Ngo Leung’s team is developing a portable device that uses neutrons to peer inside luggage and shipping containers to determine if explosive and fissile materials lurk inside.
Here’s how it works: neutron generators fire an ionized gas composed of hydrogen isotopes, either deuterium or tritium ions, at a metal target that also contains deuterium or tritium. The ions fuse with their counterparts in the target plate in a process that emits neutrons. These neutrons are then directed toward a structure, and the neutrons and gamma rays that bounce back are used to elucidate the internal makeup of the structure.
Berkeley Lab’s portable ion source is a thousand times stronger than existing devices, which allows the detection of smaller objects, faster screening, and more accurate discrimination among materials.
And as Leung explains, merely detecting the presence of potentially explosive elements such as nitrogen is not enough. That’s because some explosives aren’t composed of nitrogen. Instead, Berkeley Lab’s neutron generator can detect the precise ratios of nitrogen and other elements such as carbon and hydrogen — providing a clear picture of compounds buried deep inside shipping containers.
In addition to homeland security applications, Leung may develop even smaller compact neutron generators, perhaps to ride in robotic cars destined for Mars. “The cars could roam around a landing site, and we could use the generator to see what lies underneath Martian soil,” Leung says.
Closer to home, Leung’s team is developing a generator that could sit at the tip of an oil-well drill, allowing oil companies to see what they’re drilling through in real time. This approach is much more efficient than the current, time-consuming process, in which a borehole is drilled, the drill is removed, and a probe is inserted.
A neutron test bed