Stanford X-ray lab grows
Publication Date: Wednesday Oct 30, 1996

Stanford X-ray lab grows

Scientists use intense X-rays to probe proteins, plutonium and clams

by Heather Rock Woods

Inside a circular bunker of concrete at Stanford, a machine generates powerful X-rays that illuminate everything from the composition of nuclear waste to the three-dimensional structure of proteins to impurities in silicon chips. The X-rays at the Stanford Synchrotron Radiation Laboratory are "over a million times more intense than dental X-rays," said Gordon Brown, the head of SSRL's environmental science program.

Brown studies how small clams that live in San Francisco Bay absorb and handle selenium, a toxic element produced by oil refineries on the Bay.

Because the amounts of environmental toxins are so small, "we need extremely intense radiation," Brown said. "You drop a needle on the floor. If the light is low you can't see it, but with a small beam flashlight you have no trouble. That's a reasonably good analogy," he said.

The X-rays come from a circular pipe where electrons race around at nearly the speed of light, throwing off X-rays like a car on metal wheels would throw off sparks as it squeals around a tight corner. The X-rays are collected into beams that researchers aim at the material they are studying.

More than 1,000 people from 153 institutions carried out experiments at SSRL this year on biology, chemistry, physics, medicine, materials science and environmental science.

The lab is a division of the particle physics lab Stanford Linear Accelerator Center. But while SLAC is facing limited budgets and several rounds of layoffs, SSRL is humming with activity.

SSRL got a big budget boost last fiscal year from its main funder, the U.S. Department of Energy, allowing the lab to hire 20 more people and run experiments nine months a year rather than six. Users have a shorter wait now for beam time, but there are still more experiments than time.

"The equipment is much in demand," said SLAC spokeswoman P.A. Moore. Proposals are evaluated for scientific merit, and the best ones are awarded time on the facilities, "similar to an astronomer who wants to use a telescope somewhere," she said.

Researchers come from labs and universities in the United States and abroad and from private companies. In 1995 there were research teams from AT&T Bell Laboratories, Bristol-Myers Squibb, Chevron, Dow Chemical, duPont, Exxon, Genentech, Hewlett-Packard, IBM, Intel, Mayo Clinic, Xerox and 32 other private companies.

SSRL provides--free of charge--intense X-ray beams that can't be found in the average research lab. The apparatus starts another nine-month run on Nov. 4.

X-rays are one part of the electromagnetic radiation spectrum, which includes visible light, microwaves and radio waves. X-rays are useful for studying molecules and other microscopic things because they have smaller wavelengths than visible light. Scientists use radiation with the same or smaller wavelengths than the objects they observe.

Synchrotron radiation is simply electromagnetic radiation produced by electrons traveling in a ring. The radiation is not radioactive.

SSRL is the oldest synchrotron radiation source in the country. It started in 1974, using only whatever synchrotron radiation SLAC produced during particle physics experiments. In 1991, SSRL became independent from SLAC's schedule when it got its own source of electrons to make X-rays.

The environmental science program started then and is "going very strong," Brown said. "It and the biotech area are the two fastest growing user groups," Brown said.

In the biotech area, scientists work on understanding the structure of proteins in order to design effective drugs. "A number of compounds (studied at SSRL) are in clinical trails," said SSRL scientist Peter Kuhn.

Kuhn, a protein crystallographer, uses protein samples that are in crystal form, which means all the atoms are lined up the same way.

X-rays pass through the crystal but are deflected when they hit an atom. The deflected x-rays are measured by a detector, which produces a map of the atoms' location. From that, scientists can figure out the three-dimensional structure of the protein.

Using a Silicon Graphics workstation--like the ones used to create the dinosaurs in the movie Jurassic Park--scientists can rotate a computer model of the structure in three dimensions. Wearing $800 3-D glasses, they look for folds and dents that could be the active site where other molecules bind to the protein.

That information can help in developing drugs to block binding. For example, Kuhn and colleagues at the University of Utah have learned the geometry of the active site of a protein found in a parasite. The protein is also in humans, especially in breast cancer cells. Now Kuhn is testing a drug that acts against the cancer to see if it binds with the parasite protein.

"We want to inhibit the (protein) in the parasite (to) make this parasite malfunction." Kuhn said.

The lab caused a local stir about three years ago when a sample of plutonium--less than a gram--arrived at SSRL for research on safely storing nuclear waste. That research is continuing, and SSRL spokesman Berah McSwain stressed that "extraordinary safety precautions are taken, and the amounts are extremely small."

In fact, Brown said the lab is building a new $5 million beam line with a special clean lab to handle radioactive material.

SSRL's research helps nuclear weapons labs separate lower level waste from the most dangerous waste for long-term storage.

"It's absolutely essential to separate radioactive waste from other stuff," Brown said.



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