Seeing the unseen

From computer chips to cancer therapy How else can ion beams be used? Here’s a short list: neutron tubes can be used for boron neutron capture therapy, a two-step treatment modality for cancer that uses energetic charged particles to destroy tumor cells. For the computer industry, Leung has also developed a new selective ion source that can improve the semiconductor manufacturing process and decrease the cost of manufacturing flat-panel displays. There’s also micromachining, or using ion beams to mill and cut tiny pieces of equipment. Leung is developing an innovative technique called multifocus beam that fabricates tiny arterial stents in 40 seconds, instead of the 15 minutes usually required. And there’s lithography, a technique used to print circuits onto microchips. Leung’s group is investigating a new approach that may have a revolutionary impact in the semiconductor industry. Their approach, called maskless ion beam lithography, may give microchip manufacturers an alternative way to develop the next generation of ultra-small components, with features as small as 50 nanometers and less, or 50 billionths of a meter across. Their technique also promises higher chip manufacturing performance levels at a lower cost than conventional lithographic methods.

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

In 2002, Leung and colleagues unveiled a multipurpose neutron laboratory. The facility will serve as a test bed to determine the optimal way neutron generators can perform a variety of vital functions, such as determining whether legacy research materials contain hazardous waste, and checking luggage and shipping containers for explosives and radioactive materials. The generator uses a process called prompt gamma activation analysis, in which streams of neutrons are directed toward an object that researchers want to analyze. The facility can accommodate research that until now could only be conducted using neutrons generated at nuclear reactors.