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This article is from the In-Depth Report The Large Hadron Collider: Countdown

What Happens to Particle Accelerators After They Are Shut Down?

Radioactivity limits the potential for recycling, except for one infamous particle smasher that never saw the light of day
SSC linac



Courtesy of William Courtney, Trace Life Sciences

When physicists petitioned the U.S. Department of Energy (DoE) in the early 1980s to build a particle accelerator that would recreate the fiery conditions of the big bang, they picked a name worthy of its magnitude. The Superconducting Super Collider (SSC) located south of Dallas, Tex., would have outshined even the Large Hadron Collider, which after 14 years and $8 billion is about to start shooting particles around its 17-mile (27-kilometer) beam pipe on the Franco-Swiss border.

Slamming protons and antiprotons together at 40 tera-electron volts (40 trillion eV), the SSC would have put out more than enough energy to create the elusive Higgs boson, sometimes called the "God particle," which gives other particles their mass. (The less powerful LHC now has the honor of hunting the Higgs.) But escalating costs prompted Congress to cut the SSC's funding in 1993 before its components were even assembled.

Now, 15 years later, the SSC's sophisticated magnets are finally accelerating protons to high energy, but not for the pursuit of mysterious particles. Trace Life Sciences, based in Denton, Tex., bought the parts in 2003 to make radioisotopes for medical imaging and radiation therapy. If you have ever had a PET scan, the isotopes in your blood might have come from the most spectacular science experiment ever canceled.

The SSC's use in medicine may be unique, but the end comes for all particle accelerators sooner or later. Sooner is the operative word here in the U.S., where flat budgets have made it hard for many aging experiments to continue. Fermi National Accelerator Laboratory in Batavia, Ill., home to the leading Tevatron collider—soon to be eclipsed by the LHC—will shut down its machine in 2010. Last-minute budget cuts by Congress this year forced the Stanford Linear Accelerator Center (SLAC) in California to switch off its PEP-II collider in April ahead of schedule. What will happen to these enormous machines once they go off-line?

Once a particle accelerator is switched on, its fate is sealed as a research tool. The particle collisions that researchers scour for exotic debris also bombard the machine's metal parts with neutrons and other particles that render the metal radioactive. Neutron bombardment can convert iron and cobalt, both found in steel, into the highly radioactive isotopes manganese 54 and cobalt 60.

Given the potential health risks, the DoE does not allow used accelerator components to be put to public use, says Benedict Feinberg, a physicist at Lawrence Berkeley National Laboratory in California. So when an active accelerator retires, its parts typically get put to work on other particle physics experiments. The SSC's case was different: "When the Department of Energy pulled funding for the SSC project, the linac [linear accelerator] had never been assembled and tested," says William Courtney, Trace's director of accelerator operations.

The DoE's moratorium extends to steel reinforcements in concrete radiation-shielding blocks around an accelerator. When Berkeley's Bevatron was decommissioned in 1993, its concrete shielding went to the Relativistic Heavy Ion Collider at Brookhaven National Laboratory in Upton, N.Y. The experiment's large electromagnets, meanwhile, went to other particle research projects. Feinberg says a few steel magnet cores, some copper wiring and shielding blocks remain inside the Bevatron building. Radioactivity levels in these leftover parts and the building itself are now low enough that an April DoE environmental assessment slated the structure safe for demolition.

John Seeman, head of accelerator systems at SLAC, said half a dozen labs have requested components of the PEP-II collider, which created particles called B mesons for studying the disappearance of antimatter after the big bang. The Frascati National Laboratory in Italy is a major contender. Researchers there have proposed a more powerful version of the PEP-II experiment to the Italian government and could use almost all the PEP-II's equipment, Seeman says. Fermilab has also requested some of PEP-II's magnets for a new machine that would make high-energy proton beams for neutrino research. (When energized protons crash into beryllium targets, they create short-lived pions that decay into neutrinos.)

Fermilab intends to reuse most of the Tevatron's parts for making neutrinos, including a booster accelerator that prepared protons for entry into the main Tevatron ring, which measures 3.9 miles (6.3 kilometers) in circumference. Fermilab's deputy director, Young Kee Kim, says that the lab wants to keep the main ring in working order in hopes of reusing it for future experiments.

For the SSC, particle research was never in the stars. The state of Texas auctioned off the linear accelerator equipment in 1996 to a Denton, Tex.–based company for the bargain price of $5 million—the book value for the unused parts was over $20 million, Courtney says. Trace Life Sciences inherited the accelerator when it acquired that company in 2003.

Trace now uses the linac to accelerate a beam of protons to 32.8-mega-electron volts (3.28 million eV) and bombard up to five different targets simultaneously for different isotopes. Bombarding thallium with protons at 29 mega-electron volts (MeV) yields the isotope lead 201, which decays to form thallium 201—used in diagnosing myocardial infarctions, or heart attacks. Iodine 123 and copper 64 are used for medical imaging such as in PET scans. Graphite pieces placed in front of the 32.8 MeV beam slow the protons to the energies required for different isotopes.

The company hopes to bring online two additional accelerator stages—designed to boost protons to 50- and 70-MeV—that were not stored properly after the SSC shut down and fell into disrepair. Trace might then begin providing specialty medical isotopes such as strontium 82 and iron 52, both used in PET scans, which are currently available only from government labs.

There are advantages to working with scavenged parts from a futuristic particle accelerator that at its peak employed thousands of workers. For one thing, customer service is a breeze. When Courtney needs technical advice, all he has to do is call one of the national labs, he says, where researchers who worked on the parts are happy to offer their services.

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