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Laser light plays across a piece of cement spiked with chemical agent, creating a green "flame" of vapors and surface plasma.
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Lasers can do many things for us, from scanning barcodes at
the grocery checkout to searching for life on the surface of Mars. And, according
to chemists at Idaho National Laboratory, lasers might be able to help the
nation respond in the case of a possible chemical or radiological attack.
Lasers, the INL scientists say, could play a big cleanup
role. Lasers could help scrub chemical- or radiation-contaminated buildings
clean, returning life to normal as safely and smoothly as possible.
"Lasers could be an important tool in our
toolbox," says INL chemist Bob Fox.
Neutralizing dirty bombs: weapons of mass disruption
Fox, INL’s 2009 Inventor of the Year, has been studying
decontamination techniques for almost a decade. In the early 2000s, he joined a
Department of Defense-led effort investigating how to remediate radiological
incidents.
Fixing the damage would require decontaminating any
buildings, roads and other infrastructure that soaked up radioactive atoms (known
as radionuclides). Doing this quickly and effectively would be vital,
minimizing disruptions to people’s lives and the American economy.
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."
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A typical laboratory setup, showing the laser (right) and the illumination chamber containing contaminant (left).
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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
In the last few years, 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.
"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.
The power of light
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Ultraviolet light breaks down a chemical agent inside a quartz cuvette. The brown material is the decomposition byproduct.
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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.
Even if they’re not used to degrade VX or other agents,
lasers could still be helpful in cleanup scenarios. Laser light could blast
nasty chemicals off a wall, for example, and an integrated vacuum system could
suck them up.
"Either way, you’ve done your job," Fox says.
The porous nature of structural materials complicates
chemical decontamination perhaps more than it does radiological cleanup. That’s
because chemicals can soak deeper in —beyond the reach of laser steam-cleaning
— then seep out over time after the surface has been cleansed. But the INL team
thinks it can overcome this difficulty, too. The answer: heat.
Focusing microwaves on a point behind pooled contaminant,
Fox says, could create heat radiation that drives the chemical back out to the
surface. The technology to do this is already available, since industry uses
microwaves to cure concrete. The INL researchers will look at the effectiveness
of this technique in future experiments.
Not reinventing the
wheel
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A mass spectrometry reading shows that laser light degraded the nerve agent VX (spike at 268) into two harmless daughter products (spikes at 114 and 128).
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Using lasers to decontaminate buildings and other
infrastructure may sound futuristic. But in researching ways to strengthen our
response to potential incidents, Fox and his team are adapting established
laser technology. Lasers have been used in cleanup capacities for more than a
decade. Dentists employ them, for example, to kill periodontal bacteria and
quash mouth infections. Doctors use them to remove tattoos. And lasers have
recently become a common way to restore precious artwork.
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, not a panacea. But this tool shows great promise, and
Fox is happy to keep testing out its usefulness.
"I’m willing to shine my laser at anything," he
says.
Acknowledgement: Idaho
National Laboratory received part of its funding for this research from the
U.S. Department of Homeland Security, Directorate for Science and Technology,
Chemical and Biological Division. Work has been performed by Battelle Energy
Alliance under the U.S. Department of Energy contract DE-AC07-05ID14517.
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