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April 20, 2010

Experiments to Use Lasers Steam Cleaning of Dirty Bomb Radiation and Chemical Contamination Looks Very Promising

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Idaho National Laboratory chemists are studying the potential of lasers to help clean up chemical and radiological contamination. The goal is to increase the nation's ability to respond to "unconventional" terror attacks such as dirty bombs. Experiments are ongoing, but results thus far are very promising.

Laser technology can also scale up to perform large-scale decontamination jobs. Some cleanup and restoration firms, such as adapt laser system, are already using lasers to scrub soot off building facades. Further, these industrial operations often use automated lasers, demonstrating that laser work can be done remotely. This would minimize risks to remediation personnel responding to a terrorist attack. Fox stresses that laser decontamination is a tool in the proof-of-principle stage.

In theory, chemists already know how to clean up radiological contaminants. They can "chelate" affected areas, for instance, using grabby, reactive chemicals to wrench radionuclides off surfaces. But in the real world, that’s easier said than done. Many building materials — like cement and brick — are extremely porous. "Getting contaminants off surfaces is difficult," says INL chemist Gary Groenewold. "They start inhabiting cracks and pores." Water inhabits those cracks and pores, too, and that’s where lasers come in. Fox, Groenewold and their colleagues have shown that laser pulses can flash that water into steam, carrying the contaminants back to the surface for removal by chelation or other means. "It’s a kind of laser steam-cleaning," Fox says.

Cleaning Up Chemical Agents

The INL team has extended its work to chemical-weapon decontamination, another high national-defense priority. Nerve agents like sarin, VX and sulfur mustard are extremely dangerous, and cleaning them up can be difficult, costly and time-consuming. Most preferred methods employ other chemicals — bleach solutions, for example — which must themselves be dealt with.

Ultraviolet light breaks down a chemical agent inside a quartz cuvette. The brown material is the decomposition byproduct. "Using bleach creates a lot of secondary waste, which you have to collect and dispose of," Groenewold says. "And bleach is quite chemically aggressive, meaning it may well damage the structures you’re trying to decontaminate."

Again, lasers show promise as a possible remediation upgrade. In a series of tests still under way at the U.S. Army’s Aberdeen Proving Ground, the INL team has been using ultraviolet-wavelength lasers to scrub surfaces of sulfur mustard and VX. The tests have been successful so far, even on complex, porous surfaces like concrete.

Lasers can degrade weapons like VX in two ways: photochemically or photothermally. In photochemical decomposition, high-energy laser photons blast apart chemical bonds, slicing the agent into pieces. In photothermal decomposition, photons heat up the target surface enough to speed along natural degradation reactions. In some cases, the intense heat by itself can cause contaminant molecules to fall apart.

Some chemical agents are susceptible photochemically, others photothermally. Knowing how chemical contaminants fall apart is key, because some of their degradation products can themselves be hazardous. But according to Fox, the tests look good in this regard, too.

"The lasers are showing neutralization of agent without generation of dangerous byproducts," he says
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