Keith Hodgson

To mention the Stanford Linear Accelerator Center (SLAC), arguably one of the world's most famous particle smashers, is to invoke the essence of high-energy physics, where near-speed-of-light particle collisions reveal the inhabitants of the exotic subatomic world. Not so well-known, perhaps, is that a large portion of SLAC is run by a chemist.

Keith O. Hodgson came to Stanford University as a fledgling chemistry professor with an abiding interest in biological molecules containing metal atoms. More than 30 years later, he's still on the Stanford faculty, but he's also one of SLAC's three deputy directors and head of the center's major photon science branch.

Along the way, he defied skeptics who said ultra-bright, intense synchrotron X-rays couldn't be used for protein crystallography, and he helped turn X-ray absorption spectroscopy into one of the most useful tools available for studying organometallic structures.

Now, as high-energy physicists turn their attention to new generations of behemoth particle colliders, Hodgson is working to maneuver SLAC, which Stanford manages for the Department of Energy, into a new position at the forefront of materials science, structural biology, and chemistry. SLAC now offers a newly revamped hard X-ray synchrotron and, in 2009, will unveil what Hodgson believes will be one of the center's crown jewels: the world's first source of femtosecond-pulsed X-rays.

Back in the early 1970s, Hodgson was a bioinorganic chemist who had carved out a niche by calculating structures of organometallic complexes. His only encounters with X-rays had been the modest-strength sources in his labs at the University of California, Berkeley, where he got his Ph.D., and the Swiss Federal Institute of Technology (ETH), Zurich, where he was a postdoc. "I didn't even know what a synchrotron was," Hodgson admits.

What happened next, he says, was pure serendipity. At a Stanford seminar, Hodgson heard a physicist colleague talk about SLAC's plan to build a small facility that would allow researchers to use the sprays of bright, intense X-rays that are thrown off as electrons and positrons raced around SLAC's new accelerator ring, SPEAR (Stanford positron electron asymmetric ring). The Stanford Synchrotron Radiation Project (eventually renamed the Stanford Synchrotron Radiation Laboratory, or SSRL) would be the first synchr otron X-ray user facility in the world. Materials scientists and physicists were already excited about it, but "nobody had thought how it could be valuable for chemistry," Hodgson says.

Hodgson was inspired by the thought of what these bright X-rays, four to five orders of magnitude more intense than those produced by small lab machines, might do for his crystallographic experiments. Despite predictions that a protein crystal would be destroyed by the X-rays before he could capture any data, Hodgson borrowed the necessary equipment and set up shop at the beamline. His first diffraction experiments--with a diverse assortment of proteins, including the small electron-transfer proteins rubredoxin and azurin--quickly dispelled any doubts. "One thing was very obvious: The quality of the data and the rate at which it came were spectacular compared to what you could do with any other X-ray source," he says.

Hodgson also discovered other ways to use synchrotron X-rays in chemistry. Among them, X-ray absorption spectroscopy, for which bright, tunable synchrotron sources are ideally suited, probes the distances between metal centers and ligands. Hodgson views this application as perhaps the most important of all for chemists.

As the popularity of synchrotron radiation soared, so did Hodgson's career. By the 1980s, he was leading SSRL's structural biology program, and in 1998, he became director of SSRL.

Although sources of synchrotron radiation have proliferated (there were 10 sources in 1980; now there are more than 50), researchers at SLAC have known since the late 1980s that high-energy physicists would eventually outgrow the 2-mile-long linear accelerator and its auxiliary beams and rings. Seeking ever-higher energies, physicists see their futures at the Large Hadron Collider, opening in 2007 at CERN (European Organization for Nuclear Research) in Switzerland, and the proposed International Linear Collider at Fermilab in the plains outside Chicago.

SLAC now aims to cater to chemists, biologists, and materials scientists. The center offers a beefed-up X-ray synchrotron facility: SPEAR III, another source of hard X-rays similar to the Advanced Photon Source at Argonne National Laboratory.

Hodgson takes particular pride in SLAC's soon-to-be-completed Stanford Coherent Light Source (SCLS), a DOE-funded free-electron laser that will provide a second career for the aging linear accelerator beamline. SCLS's tight, 100-femtosecond or shorter X-ray pulses will be only one one-thousandth of the length of the bunches produced in rings like SPEAR III and will contain 10¹² photons in each pulse. That's enough to produce a scattering pattern from a single large protein molecule or capture structural changes during chemical reactions. Japan and Germany are building X-ray free-electron laser facilities, but they won't be up and running until after 2010.

"This machine will be revolutionary," Hodgson predicts. "It will be unlike anything we've had the opportunity to do science with before."

He credits the federal government, particularly DOE, for what he says is crucial support. "They are the stewards of this program," he says. "We have gotten where we are because of visionary investments."

Hodgson still maintains an active research group at SLAC that is co-run by his wife, Britt Hedman, who is a structural inorganic chemist and manager of SSRL's structural biology program. They have three papers in upcoming issues of the Journal of the American Chemical Society, "although to some degree, your science gets relegated to the evenings," he says.

His responsibilities keep growing, however. SLAC recently combined the SPEAR III and SCLS science programs under the umbrella Division of Photon Science and put Hodgson in charge. "It's exciting to be a chemist sitting in that seat," he says.