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Researchers peer into the nanoscale
Laboratory researchers have captured time-series snapshots of a solid as it evolves on the ultrafast timescale. Using the x-ray free-electron laser (XFEL) at the Deutsches Elektronen-Synchrotron Research Centre in Hamburg, Germany, the team observed the condensed-phase dynamics of an object as it undergoes laser ablation. The team’s research marks the first time that optical pulses have been used to image samples with nanometer-scale spatial resolution. Results from this research appeared in the July 2008 issue of Nature Photonics.

XFEL blasts a sample with femtosecond-long pulses, where a femtosecond is one-billionth of one-millionth of a second. Before the sample is destroyed, high-speed diagnostics record images that have a 50-nanometer spatial resolution and a 10-femtosecond shutter speed. This shutter speed, which is determined by the duration of the x-ray pulse, allows the team to observe events occurring at the atomic level before a sample is completely destroyed. “The ability to take images in a single shot is key to studying nonrepetitive behavior mechanisms in a sample,” says project leader Anton Barty of Livermore’s Physical and Life Sciences Directorate.

With the new technique, researchers can study the ultrafast dynamics occurring in noncrystalline materials under extreme conditions, such as fracture, shock, and plasma formation. The technique also allows researchers to image dynamic processes in the solid state such as nucleation and phase growth, phase fluctuations, and various forms of electronic or magnetic segregation.
Contact: Anton Barty (925) 424-4815 (barty2@llnl.gov).

Bioterrorism instrument adapted to detect tuberculosis
An instrument originally designed for detecting the malicious use of biological pathogens has a potential application in the public health sector—to rapidly screen for tuberculosis. In experiments over the past year, a Livermore research team has used single-particle aerosol mass spectrometry (SPAMS) to detect a tuberculosis surrogate, even when surrounded by sputum and mucuslike substances. The team also differentiated two similar bacteria, distinguishing an avirulent strain of tuberculosis from Mycobacterium smegmatis. The team’s research, which was funded by Livermore’s Laboratory Directed Research and Development Program, is described in the July 15, 2008, issue of Analytical Chemistry.

“We used two similar mycobacteria because many bacterial infections cause tuberculosislike symptoms, not just tuberculosis,” says lead author Kristl Adams, a postdoctoral biological physicist in Livermore’s Physical and Life Sciences Directorate. The “gold standard” diagnostic tool is to culture samples, a process that can require days to weeks. Health-care providers and emergency response personnel need a method to differentiate the infections within minutes.

With current methods, diagnosing tuberculosis can be difficult and expensive. While waiting on cultures to grow, medical personnel may release patients, allowing them to infect the general public. In addition, valuable resources may be wasted when unneeded precautions, such as chest x rays or patient isolation, are taken for people who, in the end, do not have the disease.

According to Adams, SPAMS could potentially detect tuberculosis in concentrated samples within 5 minutes, although, she notes, the team’s work is only a first step toward this application. “Having a rapid tuberculosis screening technique could improve patient care,” she says, “and reduce the toll on health-care facility resources.”
Contact: Kristl Adams (925) 424-6856 (adams82@llnl.gov).

Method distinguishes different kinds of seismic events
Using data from the Crandall Canyon Mine collapse that occurred on August 6, 2007, researchers from Lawrence Livermore and the University of California’s (UC’s) Berkeley Seismological Laboratory have successfully applied a full waveform-matching technique to determine the source of seismic events. The team’s results, which were published in the July 11, 2008, issue of Science, indicate that seismic signatures can distinguish disturbances caused by nuclear explosions, earthquakes, and collapse events.

The tragic collapse of the Utah coal mine killed six miners and three rescue workers. The 3.9-magnitude event was recorded at seismic stations operated by the U.S. Geological Survey and the National Science Foundation Earthscope USArray. “We were already developing a full waveform-matching technique to distinguish events by seismic signals,” says Livermore geophysicist Bill Walter of the Physical and Life Sciences Directorate. The research team, which included Sean Ford, a UC Berkeley graduate student and Lawrence Scholar, and Douglas Dreger, a professor at the UC Berkeley Seismological Laboratory, applied the technique to the Crandall Canyon data.

When the researchers compared recorded data to the modeling results, the Crandall Canyon seismograms clearly matched the source type for a collapse event. The team also detected Love waves, surface seismic waves that cause horizontal shifting of the earth. Love waves are typically small in large mine collapses or when a hole collapses after an underground nuclear test. In contrast, Love waves from the Crandall Canyon collapse were larger than expected for a purely vertical collapse caused by gravity. “One explanation consistent with the data is that the collapse was uneven,” says Walter, “with one side closing more than the other.”

Ford also notes that the mine collapse was relatively small in magnitude. “The fact that we could identify the Crandall Canyon event from its seismic signature gives us confidence that we can use the waveform-matching technique to identify even relatively small nuclear explosions.”
Contact: Bill Walter (925) 423-8777 (walter5@llnl.gov).


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