Spinoff is NASA’s annual publication featuring successfully commercialized NASA technology. This commercialization has contributed to the development of products and services in the fields of health and medicine, consumer goods, transportation, public safety, computer technology, and environmental resources.
Ames Research Center planetary scientist Chris McKay identifies isotopes of carbon, sulfur, and nitrogen — in that order — to search for signs of life in other worlds. “Biology does interesting things with them and leaves an isotopic signature.” The ratio of different isotopes in a carbon sample can reveal whether it’s a product of biology. Water also carries isotopic evidence of its many phase changes among gas, liquid, and solid.
The Mars Curiosity rover, for which McKay is a co-investigator, has a mass spectrometer that can identify some of these isotopes but it has to physically collect a sample and then use turbo-pumps to create a vacuum in which to analyze it. The rover’s laser spectrometer, on the other hand, can zap any surface from a distance and determine its chemical content by observing the resulting flash. For a few brief nanoseconds, the surface molecules are ripped apart in a burst brighter than the surface of the Sun, and as they reassemble, still blazing, they reveal their identities to an optical spectrometer.
Every substance emits a different light signature as its molecules reconstitute. Curiosity’s laser spectrometer can quickly and easily analyze hundreds of surfaces without the rover moving an inch, and with no moving parts, it’s likely to far outlive the mass spectrometer, even while being used much more heavily. This technique — laser-induced breakdown spectroscopy (LIBS) — has been used for decades; however, a laser ablation spectrometer can only identify chemical elements, not their isotopes.
In the early 2000s, Alexander Bolshakov, then a senior researcher at Ames, proposed fine-tuning LIBS technology to the point that it could recognize even slight shifts in electrons that result from varying numbers of neutrons in an atom’s core to spot isotopes. In 2007, he left NASA to join Fremont, CA-based Applied Spectra, which won Small Business Innovation Research (SBIR) contracts with Ames to continue the work.
The problem was that laser ablation spectroscopy is “a pretty blunt-force technique,” McKay said, while the difference between isotopes is subtle. He compares it to firing two similar cannonballs at each other and trying to observe which is heavier. For one thing, the moment when molecules in a laser-zapped sample reconstruct themselves while continuing to emit light is exceedingly brief. To have a chance at identifying isotopes, that time window had to be extended as much as possible, and the spectrometer watching it had to focus exclusively on that moment with the highest spectral resolution possible. The engineers had to shape and control the laser pulse, use the right detection sensors, and program them to observe just the right moment and the right wavelengths. Applied Spectra calls the result Laser Ablation Molecular Isotopic Spectrometry (LAMIS).
Just as isotopic signatures could reveal information in the search for evidence of extraterrestrial life, they are already mined for data on Earth. It is the key to carbon dating, which counts carbon-14 isotopes to determine the age of archeological specimens. Forensic investigators measure isotopes to match samples of hair, fabric, and other evidence.
LAMIS can analyze samples without having to collect or even approach them, which makes it useful in characterizing radioactive material used in fields like nuclear energy and nuclear medicine — dangerous material that’s better tested from afar. It could also be useful where it’s not practical to collect a sample of the material in question; for example, the shields used in nuclear cancer detection and therapy are regularly replaced because they degrade over time. To test whether the shield needs replacing, a LAMIS spectrometer would allow them to be tested and replaced only when necessary.
Detecting explosives is another application where remote sensing would come in handy; the Department of Homeland Security has expressed interest in the technology. Applied Spectra also received funding from the Department of Energy, which is interested in LAMIS for contaminated soil analysis. Even where remote sensing isn’t necessary, the technology would provide convenience and fast results, in part by eliminating the work of sample preparation.
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