In 1993, with $2 billion already spent on construction of what would have been the world's mightiest particle accelerator, the Congress killed the project, known as the Superconducting Supercollider, or SSC. All that remains are some buildings, a lot of land around Waxahachie, Tex., and a section of the planned 54-mile tunnel that would have housed the accelerator.
But a small company, International Isotopes Inc., has acquired some very expensive apparatus from the project for a song ($2.9 million), moved the machinery to its headquarters in Denton, Tex., and will soon use it to manufacture radioactive pharmaceuticals. The company says its operation will help free United States hospitals from dependence on military and foreign sources of these vital substances.
International Isotopes has modified an 80-foot-long linear accelerator, or linac, built for the SSC and will use it to make a dozen or more radioactive chemicals essential to diagnosing and treating cancer and other diseases. When a proton from such an accelerator strikes the nucleus of an atom it sometimes merges with the nucleus, changing it into a different -- and often radioactive -- element. Depending on the chemical nature of the new element, it can be used to target tumors in a specific part of the body; radioactive iodine, for example, seeks out tumors in the thyroid.
As part of the SSC, the completed linac would have given a beam of protons a preliminary shove of up to 70 million electronvolts before injecting the beam into the main accelerator ring, where the protons would have been further accelerated to 20 trillion electronvolts. The main ring was abandoned after a small section of its tunnel was dug. But the linac was nearly finished.
Carl W. Seidel, president of International Isotopes, said that his company had modified the linac to greatly increase the number of protons in its beam. The company expects to begin using the linac to make the radioactive chemicals starting in June.
The Department of Energy has encouraged the project partly because it will assure a reliable domestic source of short-lived radioactive chemicals, most of which must be used within hours of their manufacture. One such substance, fluorine-16, used to pinpoint cancerous tissue in the brain, decays so rapidly that half of any amount of it disappears in 110 minutes.
Clinicians depend partly on the production of radioactive chemicals as byproducts of Defense Department reactors, which do not operate continuously. Most of the shortfall must be obtained from foreign sources.
Doctors using radioactive substances for diagnosis and treatment must obtain these materials from reactors or accelerators that are nearby, although the longer-lived isotopes can survive short air trips. But Mr. Seidel said his company would use its linear accelerator as a prototype for similar accelerators it would build for sale or lease.
High-energy physicists continue to lament the demise of the SSC. But President Clinton, who signed the legislation that killed the project, has had second thoughts. In June, after the discovery of mass in neutrino particles, Mr. Clinton told students at the Massachusetts Institute of Technology that the discovery ''calls into question the decision'' to abandon the project.
Photo: Part of the Superconducting Supercollider is being used to produce radioactive pharmaceuticals. (Jarrold Cabluck for The New York Times)