June 25, 1999 When Joni Mitchell, in her song "Woodstock," sang, "We are stardust..." she was being factual as well as poetic. Every element on earth, except for the lightest, was created in the heart of some massive star.
And the heaviest elements -- such as gold, lead and uranium -- were produced in a supernova explosion during the cataclysmic end of a huge star's life, says LSU physicist Edward Zganjar (pronounced Skyner).
"Those elements were ejected into space by the force of the massive explosion, where they mixed with other matter and formed new stars, some with planets such as earth. That's why the earth is rich in these heavy elements. The iron in our blood and the calcium in our bones were all forged in such stars. We are made of stardust," Zganjar said.
Zganjar should know. He is studying just how the heavier elements are made in supernova explosions -- the pathways matter takes as it is transformed from a lighter element to a heavier element during the cosmic alchemy.
He was recently awarded more than half a million dollars by the U.S. Department of Energy to study "the structure of nuclei far from stability."
The grant funds a continuation of the work he has been doing at the Holifield Radioactive Ion Beam Facility at the Oak Ridge National Laboratory in Oak Ridge, Tenn.
The radioactive ion beam accelerator smashes a projectile atom into a target atom in order to fuse the two nuclei. The resulting collision between the nuclei of these atoms creates unstable elements that often last only milliseconds before decaying into other elements. The collision of iron-54 with calcium-40, for instance, creates an unstable nucleus of palladium-94, which breaks up into a number of other unstable elements. Depending on statistical probabilities, these elements undergo radioactive decay, with the process eventually stopping with the production of stable, non-radioactive elements. It is these early nuclei that are of primary interest, and that is what is meant by "the structure of nuclei far from stability."
Zganjar's group recently completed work on a particularly critical nuclide, Zirconium-80, which lies along the path astrophysicists call the rp-process.
This was a difficult experiment, Zganjar said, made successful by the instrumentation developed by his group. "We might produce only one out of a billion of what we're looking for, then we have to separate it from all the other reaction products -- junk. And the decay process might last only a microsecond, so we have to study them fast." That is what the instruments he has developed enable him to do.
Zganjar will use the newly developed techniques and instrumentation to study even heavier nuclei along the rp-process path. He is now making preparations to study the next heavier rp-process, Molybdenum-84.
"Doing this gives us a much better understanding of the structure of matter. The structure of matter underlies the structure of the whole physical cosmos," he said.
Current understanding of the process by which heavy elements are produced in massive stars has, up to now, been largely based upon theoretical predictions. But with radioactive ion beam detectors and the new spectroscopic techniques developed by Zganjar and his team, scientists are able to mimic some of the reactions taking place during supernova explosions and measure in the laboratory quantities that could previously only be estimated by theorists.
"Understanding the universe and humanity's place in it has always been a primary focus of human inquiry since the time of the caveman. What we're doing at Oak Ridge can provide a piece of the puzzle of the origin of the elements that make up the entire universe," Zganjar said.
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