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Nuisance Sometimes Has an Enlightening Silver Lining

March 15, 2001|K.C. COLE

BERKELEY — Like many big brothers, my son used to think of his kid sister as little more than a nuisance. Then one day, an older boy wised him up: "Be nice to your sister," he said. "One day she'll have money; she'll have friends."

Science, too, has learned how to cash in on the bright side of a nuisance.

One of the biggest nuisances for accelerator physicists has always been something called synchrotron radiation. Accelerator physicists are the folks who push tiny subatomic particles around in "racetracks" up to nearly the speed of light. When the particles collide either with one another or with stationary targets, they can create exotic forms of matter--revealing fundamental properties of nature.

Synchrotron radiation is the light that leaks off the subatomic particles circling around huge rings. The more light that radiates away, the less energy is left in the particle beam to collide with other particles.

In the early days of accelerators, synchrotron radiation was just one of those nuisances--like kid sisters--that physicists had to deal with. For some, it's still an obstacle. In modern machines, in fact, the radiation can be powerful enough to fry sensitive electronics, cause cables to crack, hoses to leak.

But other scientists learned how to make a proverbial silk purse out of a sow's ear--using synchrotron radiation as a light source for looking in on the hidden mechanisms of atoms, molecules and materials.

At first, these "synchrotron light sources" were mere parasites siphoning off the discarded light from particle accelerators. Today, they are special purpose machines, precisely tuned to produce consistent, pure and highly concentrated packets of light.

The first of this breed to be built was Lawrence Berkeley Laboratory's Advanced Light Source, overlooking San Francisco Bay. As electrons whirl around inside a ring with a diameter two-thirds the length of a football field, they get nudged by powerful bending magnets, as well as "wigglers" and "undulators." And any time an electron is forced to change direction, it sends out radiation, or light. (It's the same wiggling of electrons that produces the light from the sun, as well as the radio waves that bring the sound of your local DJ into your car.)

Once produced, thin slices of the spectrum of light can be diced off and directed to targets at a specific experimental area. The target might be a bit of mud that scientists might be probing it to see if toxic contaminants are present, and if so, what molecular mechanisms transport pollutants from place to place; or it might be a new material with promising magnetic properties, destined for the next generation of computers.

Arriving at targets in precision pulses, these bullets of light can knock an electron out of an atom, or hit an atom with just the right energy. They can deconstruct molecules like Tinkertoys, peeling off one layer of electrons at a time, to reveal their inner structure.

"You can roam around inside a complex material," as UC Davis physicist Charles Fadley described it. This makes it perfect for unraveling the tangled knots of proteins or understanding how superconductors work.

Astronomers even use the Advanced Light Source to calibrate their instruments, because synchrotron radiation shows up wherever electric charges are pushed around at high speeds--circling Jupiter, or orbiting a black hole, or streaming from an exploding star.

Ironically, the Advanced Light Source was built directly beneath the landmark dome of Ernest O. Lawrence's World War II cyclotron that dominates the hillside.

To Lawrence, of course, radiation leaking from his accelerator was nothing but a bother.

Which just goes to show that at least some of the time, life's everyday irritations can have a lot more than mere nuisance value.


Cole can be reached at

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