June 22, 2010

Early results from the world's brightest X-ray source

SLAC's Linac Coherent Light Source probes nitrogen molecules

The SLAC linear collider in Menlo Park, California has already made a name for itself as one of the world's largest and most prolific particle accelerator facilities dedicated to high energy particle physics. It is now beginning a new life as a source of x-rays a billion times brighter than any other research x-ray source to date. Early results that reveal how molecules respond to intense radiation from the facility's Linac Coherent Light Source (LCLS) are set to be published this week in the journal Physical Review Letters.

The early LCLS research takes advantage of the machine's bright, brief flash to study how x-rays strip electrons from molecules built of pairs of nitrogen atoms. Once the electrons are removed, the nitrogen atoms strongly repel each other, and the molecule rapidly blows apart. But in addition to being very bright, the x-ray pulses from the LCLS can be made extremely brief, which allows researchers to capture data from the molecule before it disintegrates. The result is the x-ray equivalent of a flash bulb that freezes the action in a photograph. Unlike photographic flashes that are thousandths of a second in duration, however, flashes from the LCLS are measured in femtoseconds, which are a millionth of a billionth of a second long.

In some of the first published results to emerge from the LCLS, the researchers report that nitrogen molecules absorb less x-ray radiation when illuminated with shorter flashes compared to longer ones. In addition to helping develop a model for x-ray absorption in molecules, the results show that the LCLS will likely be able to provide snapshots of never-before-seen, ultra-fast chemical and molecular processes, including those involving the biomolecules that are critical components in living cells.

APS Physics
APS Physics publishes expert written commentaries and highlights of papers appearing in the journals of the American Physical Society.