Science/Medicine : Berkeley scientists find new--and lucrative--uses for an aging, obsolete Atom Smasher
BERKELEY — It was a great machine, the mighty Bevatron. Less than two years after it was switched on in 1954, the billion-electron-volt particle accelerator--the most powerful atom smasher in the world at the time--did precisely what it was designed to do. It discovered an arcane slice of the universe called antimatter, thus confirming complex mathematical models of how the universe really works.
At the same time, it made itself obsolete.
Once it had smashed subatomic protons together with enough energy to create antiprotons and antineutrons--small atom fragments with characteristics that are the exact opposite of normal--the barn-sized Bevatron was a multimillion-dollar machine with no clear task.
Rather than junk the machine, or cannibalize it for parts to build a larger accelerator, clever and curious physicists at the Lawrence Berkeley Laboratory retooled the Bevatron, rechristened it the Bevalac and then put it back on the cutting edge of physics research.
It is perhaps the best example of what can be done with old atom-smashers--a subject of special concern as Congress debates whether to spend $4.4 billion to build the most powerful particle accelerator ever, the new superconducting super collider.
An old electron accelerator at Stanford, for example, has been converted to a synchrotron light source. This device is similar to an X-ray machine and has become popular among corporate and government clients for analyzing the inner structure of new composites and other materials.
“Each (electromagnetic) wavelength can explore a different property in the structure of matter,†said Edwin (Ned) Goldwasser, associate director of the SSC Central Design Group at the Lawrence Berkeley Laboratory here. “Things we can see in X-ray . . . are things we can’t see at a higher-energy (wavelength) or a lower energy, and vice versa.â€
Corporate and government researchers also are paying customers at an old University of California, Davis, proton accelerator. The 60-inch cyclotron was built at the University of California, Berkeley, by Ernest O. Lawrence, who won the Nobel Prize in 1939 for inventing and developing such machines. The 48-year-old machine now is used for several commercial applications: to analyze air-pollution samples, measure acid rain, make nuclear medicine to fight cancer and even authenticate the inks and papers of old documents.
To be sure, dozens of old accelerators have done their duty, been dismantled and forgotten. Others have been cannibalized for their parts, especially their big iron magnets, which usually are employed in the massive computerized detectors that analyze the collisions in new accelerators.
However, a surprising number of old machines--nearly a dozen were located in an informal survey by The Times--still have science to do, either as an element in a more modern accelerator, as synchrotron light sources, opening up vistas in nuclear science or developing new cancer treatments.
Of all of them, the Bevatron may be the best example, Goldwasser and others said.
“The interesting thing is that in the 30 years following (the discovery of antimatter), the facility has somehow been able to stay on the cutting edge of particle research,†said Charles Hurley, a spokesman at the Lawrence Berkeley Laboratory, which includes three other operating atom smashers, as well as the original five-inch cyclotron invented by Lawrence in 1930.
“It shows that you can’t predict the opportunities that can arise when you build these facilities and staff them with imaginative people,†Hurley said.
Perhaps the most imaginative use for the Bevatron arose in the early 1970s, when the machine was modernized and linked up with another nearby accelerator, a heavy ion linear accelerator. Together, the two machines, known collectively as the Bevalac, accelerate entire atoms--even the heaviest uranium isotopes--to nearly the speed of light.
For nuclear physicists and astrophysicists, this is a useful advantage over regular accelerators, which use only fragments of hydrogen and other extremely light atoms.
“From two such ancient parts, we created this unique machine,†said James Symons, associate director of the federal facility’s nuclear science division, “and it is still unique today, although other machines are now being built to do the same thing.â€
He said the ability to accelerate heavy ions lets scientists approximate on a small scale a number of curious space phenomena, such as the extreme nuclear densities experienced after a star collapses in on itself in a supernova.
Nuclear physicists, he added, use the accelerator to work on formulating an equation of state for nuclear matter--that is, to see if atomic nuclei change states, as water molecules change into ice and steam. This is done by smashing together heavy ions to generate very high temperatures and pressures, and make atom fragments with extreme numbers of protons or neutrons.
Biomedical researchers, meanwhile, use the Bevalac’s heavy-ion capabilities in two fields, radiation biophysics and radiobiology--the study of the effects of radioactive substances on living organisms.
Other scientists use the accelerator to operate a Heavy Ion Superconducting Spectrometer, a basic research tool used to analyze the makeup of materials by bombarding them with highly charged atoms. Still others use the accelerator to test artificial satellite equipment by exposing it to simulated cosmic rays.
The most easily understood Bevalac pursuit could be the cancer radiotherapy program. Here, scientists use high-energy ionized beams of neon, silicon and other elements to destroy malignant tumors found in areas precluding treatment by surgery, chemotherapy or X-ray. Cancers found along the spinal column would be one example, said Bob Stevenson, the Bevalac’s deputy operations manager.
Researchers found that heavy ions--relatively large atoms stripped of some or all of their electrons--caused little damage to human tissue while moving, but a lot of damage as they grind to a stop. After learning a tumor’s location within the body, operators can “focus†a heavy-ion beam and zap the tumor by giving the ions enough energy to pass right through healthy tissue and come to rest inside the cancer.
At the Bevalac, experimental research trials are under way on a variety of cancers--lung, prostate, brain, bone and even melanoma in the eye.
“For certain kinds of tumors--not all, but some--this is a very promising program,†said Dr. Joseph Castro, a research oncologist from the University of California, San Francisco, Medical School. Beam treatment is more effective on cancers that are surgically inaccessible or unresponsive to chemotherapy.
“There hasn’t been a lack of things to do with it,†Symons said.
Usually, several of these activities take place at virtually the same time, even when one user requires a beam of, say, uranium ions and another employs a beam of lighter argon ions. Stevenson said the beams can be switched over in a minute, making the accelerator even more useful by making it available to even more users. The Bevalac has a $17-million-a-year operating budget paid chiefly by the U.S. Department of Energy.
No machine lasts forever, however. Not even the venerable Bevatron.
Symons and others noted that the Bevatron has been significantly rejiggered twice--in 1960, when a new source device increased the number of particles that could be accelerated, and in 1980, when an improved vacuum liner permitted the acceleration of heavier ions. They believe it may now be cheaper to replace it entirely than to attempt further improvements. The laboratory is preparing a proposal to replace the accelerator by 1994, its 40th birthday.
“It’s been a great machine, the Bevatron, and it has maybe five more years left in it,†Symons said. “Of course, they’ve been saying that for more than 20 years now.â€
HOW THE PROPOSED $4.4 BILLION SUPER COLLIDER WOULD WORK
1. Hydrogen atoms are electrically charged (ionized) so they can be aimed with magnets.
2. The ions are injected into a linear accelerator (LINAC) which uses pulses of radio waves to accelerate them much as waves at the beach accelerate surfers.
3. At the end of the LINAC, the ions are swept into a low-energy booster that strips away the atoms’ two electrons, leaving electrically charged protons.
4. The protons are further accelerated in the medium-energy booster, and then in the high-energy booster.
5. In the double-barrelled main ring, thousands of extremely strong, 50-foot-long magnets keep the two powerful proton streams in alignment as they travel in opposite directions at nearly the speed of light. The streams are about the thickness of a drinking straw.
6. In “collision hallsâ€--warehouse-sized laboratories--focusing magnets reduce the streams to less than the width of a human hair. The opposing streams are aimed at each other to create the collisions.
HOW BERKELEY’S BEVALAC WORKS
The Bevalac--a combination of the Bevatron and SuperHILAC working in tandem--is the only accelerator facility in the world that provides ions as heavy as uranium at velocities close to the speed of light.
1. Heavy ions are produced and accelerated at the SuperHILAC--a linear accelerator--then steered through a transfer line into the Bevatron.
2. In the circular Bevatron, the heavy ions are further accelerated and then routed to various research areas, including a trial program of heavy-ion cancer therapy.
