Toward X-ray movies

Low-power tabletop source of ultrashort electron beams could replace car-size laboratory devices.

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Ultrashort bursts of electrons have many important uses in scientific imaging, but producing them has typically required an expensive car-sized apparatus.

In the journal Optica, researchers at MIT, the German Synchrotron, and the University of Hamburg in Germany describe a new technique for generating electron bursts, which could be the basis of a shoebox-sized device that uses a much smaller amount of power.

These beams are used to directly gather information about materials that are undergoing chemical reactions or changes of physical state. But after being fired down a particle accelerator a half a mile long, they’re also used to produce ultrashort X-rays.

Last year, the same group of MIT and Hamburg researchers reported the prototype of a small “linear accelerator” that could serve the same purpose as the much larger and more expensive particle accelerator. That technology could bring the imaging power of ultrashort X-ray pulses to labs.

While the electron bursts reported in the new paper have a duration measured in quadrillionths of a second, the researchers’ approach has the potential to lower their duration to a single femtosecond. An electron burst of this size could enable real-time imaging of cellular machinery in action.

“We’re building a tool for the chemists, physicists, and biologists who use X-ray light sources or the electron beams directly to do their research,” says Ronny Huang, an MIT PhD student in electrical engineering and first author on the new paper. “Because these electron beams are so short, they allow you to kind of freeze the motion of electrons inside molecules as the molecules are undergoing a chemical reaction. A femtosecond X-ray light source requires more hardware, but it utilizes electron guns.”

Ultrashort X-ray pulses have the same advantages that ordinary X-rays do: They penetrate more deeply into thicker materials. The current method for producing ultrashort X-rays involves sending electron bursts from a car-sized electron gun through a billion-dollar, kilometer-long particle accelerator that increases their velocity. Then they pass between two rows of magnets — known as an “undulator” — that converts them to X-rays.

The paper published last year described a new approach to accelerating electrons that could shrink particle accelerators to tabletop size.

Get the full story here.

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