Table of Contents
Send a Letter
Magazine Staff
Editors's Notes
Chicago Journal
Course Work
Class News
Books by Alumni
For the Record
Center Stage
Virtual Chicago
Alumni Gateway
UofC Homepage

Traveling at 299,000 kilometers per second, electrons at the Advanced Photon Source provide energy for 70 X-ray beams that are lighting the way for unprecedented research.


By Diana Steele


In the University of Chicago’s backyard, in what was once an empty field at Argonne National Laboratory in DuPage County, sits one of the world’s most powerful research instruments, the Advanced Photon Source (APS). Six years and nearly $1 billion in the making when it opened in 1996, the Advanced Photon Source—managed by Argonne, which in turn the University of Chicago manages for the U.S. Department of Energy (DOE)—is essentially a very intense X-ray machine.

Highly focused and extremely bright, the X-ray beams produced at the APS are a trillion times more brilliant than the first X-rays produced 100 years ago. They depict structures in far greater detail and much faster than previously possible, doing in microseconds what once would have taken days. The brilliance of the APS beams allows scientists to examine tiny samples that could not have been seen with earlier X-rays. Produced in short bursts lasting only 60 billionths of a second, they also let researchers observe physical, chemical, and biological processes that occur extremely quickly.

Because the APS X-rays are among the most powerful and widely applicable research tools available, scientists conducting experiments there expect to change the face of technology in areas from medicine to manufacturing, agriculture to the chemical industry. When the APS—by far the most powerful photon source in the U.S.—becomes fully operational, more than 4,000 researchers from the U.S. and abroad will be able to harness its power through 70 separate beamlines.

“We are engaged in a collective and dynamic enterprise with the potential to see and understand the structures of the most complex materials that nature or man can produce—and that underlie virtually all our modern technologies,” wrote David Moncton, the Argonne associate laboratory director in charge of building the APS, in his introduction to an APS brochure. “From this primordial soup of scientists exchanging ideas and information come the collaborative and interdisciplinary accomplishments that no individual alone could produce.”

One of more than 40 photon sources in operation worldwide, the 7 GeV (7 billion electron-volts) APS is matched only by Japan’s 8 GeV Super Photon Ring (SPring-8) and the 6 GeV European Synchrotron Radiation Facility (ESRF) in France. In the U. S., the DOE has three other synchrotron radiation facilities besides the APS, and a handful of universities have their own. Like the SPring-8 and the ESRF, the APS is called a third-generation source because it’s designed to accommodate advanced equipment that provides more brilliant beams.

“A decade ago, we set out to design and construct what we hoped would be the most powerful, versatile, and user-friendly machine that was technically possible,” says Moncton. “I hoped that achievement would be second only to its scientific output over the next decade, and everything that we’ve seen in the first year or so would lead us to believe that will be the case. The quality of the early work is extraordinary.”

A November 1997 report by the advisory committee to the DOE’s Office of Basic Energy Sciences agreed: “[The APS] will be the premier hard X-ray facility in the U.S. and indeed the world for the foreseeable future.”

The APS can be applied in virtually every scientific field to solve real-world problems as well as conduct basic research. Geologists are looking at samples of the earth’s crust to see how it was formed. Biologists hope to use the APS to understand the shapes of biomolecules, such as viruses, and thus control their function. Materials scientists can study the formation of superconducting ceramics—which could be the equivalent of a silicon chip to the communications, space, and auto industries—and develop “soft” materials such as lubricants, paints, and food additives. In chemistry, manufacturing, physics, and medicine, researchers can use the APS to try to design artificial photosynthetic systems; mass produce micro-electromechanical devices; create new kinds of atomic ions; and improve the speed, clarity, and safety of medical diagnostic tools. And that’s just a sampling.

So far, much of the APS researchers’ time during the past two years has been devoted to perfecting beamlines and to building instruments, but many studies are already under way. Currently, 20 of the 35 research sectors at APS are up, with some 1,200 scientists at work, and two more sectors beginning to construct experiment stations. Collaborative access teams, or CATs, operate one or more sectors. Each of the 15 current CATs is made up of dozens of researchers from different universities, national laboratories, and corporations responsible for designing, building, funding, and operating experimental stations at the APS. The Biophysics CAT, managed by the Illinois Institute of Technology, is looking at insect flight muscle patterns and the structure of metalloproteins. At the DuPont–Northwestern–Dow CAT, scientists concentrate on the atomic structures of surfaces, interfaces, and thin films, plus polymer science and technology. The IBM–McGill–MIT CAT focuses on dynamic phenomena in materials science and condensed matter physics.

The Consortium for Advanced Radiation Sources (CARS), the University of Chicago CAT, was one of the first to begin work and this past October held a grand opening ceremony with speakers, tours, and a dedication. CARS stands out among the APS teams because of its size and interdisciplinary nature. With biochemistry and molecular biology professor Keith Moffat as executive director, CARS brings together more than 140 investigators from the U of C, Northern Illinois University, Southern Illinois University, the Australian Nuclear Science & Technology Organization, and other institutions across the U.S. to study biological and chemical materials and to do research in geophysical science.

Moffat likens the APS to a scientific mecca: “There’s a certain advantage to being Mecca. We have all the experts in how to design and use the experiments. Everyone comes to us, and it means Chicagoland is the place to go in the United States and the world to do these kinds of experiments.”

The microexplorations take place in a macro building that’s played cameo roles in the recent pseudoscientific films Chain Reaction and Mercury Rising. Seen from above, the APS structure resembles a gigantic concrete doughnut. Just over one kilometer in circumference, the building is large enough to encompass Wrigley Field. The researchers’ preferred form of indoor transportation is oversized tricycles.

The heart and possibly the soul of any photon source is its central storage ring, where the X-rays are created. First, pulsing streams of electrons are ejected from an electron gun into a linear accelerator that raises their energy level. The electrons are injected into a synchrotron booster and then into the central storage ring, which isn’t a perfect circle but rather a set of curves connected by straight sections. Essentially a huge vacuum pipe, the storage ring is emptied as completely as possible: As little as one atom out of every trillion present in normal atmosphere remains. Maintaining a constant intensity X-ray beam requires that the electrons travel without striking even something as small as a gas molecule.

Next, 45 five-meter-long “bending” magnets tease the electrons around the ring’s curves at nearly the speed of light, with the particles traveling the 1,104-meter circuit more than 271,000 times every second. It’s like automobile tires squealing as kinetic energy gets converted to sound on a curve taken too fast: The electromagnetic field synchronizes and accelerates the electrons, making them “squeal” around the ring as kinetic energy gets converted to light energy—beams in the form of high-energy X-ray photons.

Third-generation storage rings differ from their predecessors by having two additional kinds of magnets, undulators and wigglers. Undulators maximize brilliance—a measure of the intensity and directionality of an X-ray beam—while wigglers increase flux—the number of photons per second passing through a defined area. Undulator magnets produce very brilliant radiation at a particular, tunable wavelength, while wiggler magnets produce a highly directional beam with a wide range of wavelengths—like the white light from a lightbulb. Undulators are useful for almost all kinds of experiments; wigglers are used for only very specialized experiments, such as studying the interaction of polarized light with magnetic materials. Because they are inserted in the straight sections of the storage ring, between the bending magnets, undulator and wiggler magnets are called insertion devices.

The experiment sectors, which are positioned along lines tangent to the storage ring, each receive two X-ray beamlines, one from an insertion device and one from one of 35 additional bending magnets that produce radiation covering a broad, nearly continuous spectrum. Each group of researchers uses the same basic techniques—X-ray imaging, X-ray scattering, X-ray spectroscopy, and time-resolved X-ray studies—to explore a diverse array of mysteries they hope soon to unravel.

Researchers at CARS are using the power of the APS’s X-ray beams to reveal the makeup of moon rocks and to take pictures of molecules in action—possibly helping to build a better battery and other practical products. CARS fills three APS sectors: GeoSoilEnviroCARS, which does geophysical sciences, plus soil and environmental research; BioCARS, devoted to the study of biological materials; and ChemMatCARS, still in the design phase, which will study the structure and properties of chemicals and materials.

Stationed at sector 13, GeoSoilEnviroCARS researches the composition, structure, and properties of earth and planetary materials, the processes that produce them, and the processes they control. Right now, two main instruments are operational: an energy-dispersive diamond anvil cell with laser heating and a microprobe capable of fluorescence analysis, spectroscopy, and microtomography.

With the high-pressure diamond anvil cell, researchers hope to better understand the structure of the earth’s core. By using the diamond anvil cell to squeeze a sample such as iron under the same intense pressures found at the earth’s center, they intend to discover the core’s composition and properties. “There must be some light elements in the core,” speculates Mark Rivers, CARS associate director and senior research associate in geophysical sciences. “But exactly how much of those light elements there has to be and what they are—oxygen, sulfur, or something else—isn’t known.”

The high-energy X-rays produced by the APS penetrate the diamond anvil cell, then scatter from the small sample of material held within the cell, revealing the sample’s atomic structure at earth-core pressures. The diamond anvil cell also lets scientists study the transition from solid to liquid at the earth’s outer core. To try to calculate the melting point of iron at these high pressures, researchers use a special laser to heat minute samples in the diamond anvil cell, then view the reaction with the X-ray beam.

With the microprobe, scientists are measuring trace element compositions to study soil contamination. The brilliance of the APS beamlines lets GSECARS researchers focus on a spot as small as 1 micron across, about one-hundredth the width of a human hair. In these tiny spots, concentrations of elements as low as 10 to 100 parts per billion can be measured. Such exquisite sensitivity should be useful, Rivers says, in figuring out how to remedy soil contamination: Such soil can be studied, treated, and then re-examined to see how well a particular clean-up method works.

The microprobe also lets researchers search for clues to cosmic history by studying the composition of meteorites, moon rocks, and interplanetary dust from Earth’s upper atmosphere. “The ultimate goal,” says Steve Sutton, CARS associate director and senior research associate in geophysical sciences, “is to find out what the conditions were during the formation of the solar system. Were there gradients of temperature and composition? How has the material been processed since that time?” Looking for more clues, the NASA spacecraft Stardust, scheduled for launch in 1999, will make the first sample-return mission to a comet; GSECARS scientists plan to analyze the cometary dust it collects when the spacecraft returns to Earth in 2006.

Around the bend in sector 14, the BioCARS scientists are looking inward rather than outward. The focus here is on crystallographic studies of enzymes, hormones, viruses, proteins, ribosomes, and other macromolecular complexes. By understanding the structure of these complexes, scientists will be able to comprehend—and perhaps even control—bio-logical processes; for instance, how proteins transport oxygen in the blood or build muscles. Groups from around the world are already heading to the BioCARS facilities to conduct such investigations, which could lead to medical, pharmaceutical, and biotechnological breakthroughs—maybe designing a drug to block the active sites of all common cold viruses or improving an enzyme’s ability to clean up sites contaminated by oil or industrial waste.

But the true mission of BioCARS is to do groundbreaking science, while letting other researchers use the BioCARS facilities to study more specific problems. “It’s extremely important for BioCARS to conduct frontier research,” says Keith Moffat, the principal investigator of BioCARS, “to do the experiments that are very difficult, as distinct from experiments that apply today’s techniques very effectively.”

Most of the BioCARS work is done by X-ray crystallography, in which billions of closely packed copies of a protein diffract X-rays, allowing scientists to discern a macromolecule’s structure by the observed X-ray intensity. For the technique, molecules must be crystallized.

BioCARS researchers are pushing the frontiers of crystallography to examine dynamic phenomena that happen very rapidly, in addition to looking at larger macromolecular structures and tinier crystals. With the high-power, pulsed APS beams, X-ray exposure times have dropped significantly—which means researchers can take “stills” of the most minute changes during a biological or chemical process.

“We can record structures now with nanosecond time resolution, which is extremely important, because lots of things in chemistry and biology happen very quickly,” Moffat says. “When we began this work, we were lucky if we got time resolution of seconds.” So far, APS researchers have done this kind of time-resolved crystallography on myoglobin, hemoglobin, and photoactive yellow protein.

When it comes to viruses, BioCARS is the place to do research—it’s home to one of only two synchrotron-based biosafety level three centers in the world, able to handle bacterial, fungal, and viral agents such as salmonella, all forms of hepatitis, rabies, yellow fever, or equine encephalitis. Some of the BioCARS researchers are examining proteins contained in the HIV virus, though nobody has been able to crystallize the entire virus. This past fall, John E. Johnson of the Scripps Research Institute used data collected at BioCARS to make a complete tracing of all capsid proteins contained in the Hong Kong 97 virus that contaminated Hong Kong’s poultry population in 1997, necessitating that every chicken in the country be killed.

With the BioCARS facilities at the APS, notes Wilfried Schildkamp, CARS associate director and senior research associate in the biochemistry and molecular biology department, scientists can now examine viruses three times as large and 30 times as complex as those that could be studied ten years ago. And with a technique called multiple wavelength anomalous dispersion phasing—which involves measuring the same protein at different wavelengths—scientists can determine a protein’s structure much more easily.

“Structures that typically took years to solve now take less than a month,” says Schildkamp. “With this technique—and an optimized beamline—you can crack nearly every structure there is.”

Scientists have equally ambitious plans for the youngest CARS sector, ChemMatCARS, in station 15, hoping to conduct their first experiments by January 1999 and to be fully operational one year later. The chemical and materials research conducted there is expected to make major contributions to the understanding of surfaces, polymers, thin layers, and interfaces—the stuff of such modern in- dispensables as data storage, adhesives, and batteries. Construction has already begun on the sector’s three experiment stations.

The first, the chemical crystallography station, will be devoted to a very high-resolution study of the structure of chemical crystals. For example, scientists will examine small-molecule crystals—like those found in superconducting ceramics—to learn how the contours of the electrons reflect different types of bonding and how bonding changes as the system is perturbed by light or electric and magnetic fields.

At the surface science station, researchers will look at the dynamics and properties of soft surfaces and liquids. In liquid-surface scattering experiments, researchers will focus on the structures at the interfaces between different liquids (the boundary between oil and water, for example), liquids and solids, and liquids and gases. Little is known about what happens at these interfaces, although many important processes—including electrochemistry and corrosion—occur there. A better understanding of these processes could lead to such developments as new battery technologies.

The third station will use small- and wide-angle X-ray scattering to study the internal structures of materials like polymers and composites. Scientists will reexamine both the atomic scale and mesoscale structure of polymer-based surfaces, filaments, and strands. Able to see the atomic and molecular building blocks of such structures in much greater detail than ever before, scientists can learn how structures arrange themselves to form new polymeric materials.

“The APS is a source with a very tiny cross-section and a gazillion photons coming through. In addition, it’s tunable to different wavelengths and very well-defined,” says Stuart Rice, the Frank P. Hixon distinguished service professor in the James Franck Institute, the chemistry department, and the College, and ChemMatCARS principal investigator. “We’ll be limited only by our imagination in the types of experiments we can conduct.”

David Moncton agrees with Rice, commenting that the APS pushes what’s possible so far beyond the previous threshold that the science being done there is “revolutionary.” Right now, he says, “there’s a prodigious supply of data being generated, that has been generated over the last year,” adding that “there’s a huge range of experiments now that have demonstrated the promise of this machine in quite tangible scientific terms.” A number of these “cameo” experiments have already yielded publications: By the end of a decade, he predicts, the aggregate impact of the work being done at the APS will be evident.

For Moncton, the Advanced Photon Source represents only the latest, far from final, step in X-ray technology. He envisions an X-ray “laser” in which all of the X-ray photons are not only all moving in the same direction but also have a single wavelength and pulse at speeds a thousand times faster than the APS. Such a tool might make possible holographic imaging of the atomic structure of single atoms, or stop-action photography of the transfer of electrons during photosynthesis—one of nature’s fastest processes.

Scientists, notes Moncton, aren’t waiting for the APS honeymoon to end before moving on to the next new thing: At Argonne, preliminary steps in developing a fourth-generation light source are already under way.

Table of Contents | Send a Letter | Staff | Editor's Notes | Letters | Investigations | Journal | Class News | Books | Deaths