Counting Atoms That Aren't There, In Stars That No Longer Exist

Argonne scientists, in collaboration with colleagues at the University of Chicago, Washington University and the Universita di Torino in Italy, examined stardust from a meteorite and found remnants of now-extinct technetium atoms made in stars long ago.

The stardust grains are tiny bits of stars that lived and died before the solar system formed. Each grain is many times smaller than the width of a human hair, and carries a chemical record of nuclear reactions in its parent star.

Famed scientist P.W. Merrill fifty years ago observed the signature of live technetium - an element that has no stable isotopes - in the starlight from certain types of stars, thereby proving the then-controversial theory that stars make atoms via a process called nucleosynthesis. The researchers' discovery that their stardust grains once harbored live technetium brings the science of nucleosynthesis full circle.

"Finding traces of technetium decay products in stardust provides a very precise confirmation of the theories of how atoms are made inside stars," said Michael Savina, Argonne scientist and the lead author on the research, which is published today in Science. "The fact that we can both predict and measure very tiny effects in the chemistry of these grains gives us a lot of confidence in our models of how stars work."

Authors on the report, in addition to Savina, are Michael Pellin and C. Emil Tripa of Argonne, Andrew M. Davis and Roy S. Lewis of the University of Chicago, Sachiko Amari of Washington University in St. Louis, and Roberto Gallino of Universita di Torino in Italy. Funding was provided by the U.S. Department of Energy Office of Science, the University of Chicago, NASA, and the Italian FIRB Progetto Origine Astrofisica degli Elementi Pesanti Oltre il Ferro.

The work was made possible by a specialized instrument at Argonne called CHARISMA, the only instrument of its type in the world. "CHARISMA is designed to analyze very tiny samples – the kind where you can't afford to waste atoms, because there are so few of them to work with," Savina said.

CHARISMA is presently being upgraded, with funding from the Department of Energy Office of Science and from NASA, in anticipation of samples from the Genesis mission to collect samples of the solar wind – single atoms and electrically charged particles from the sun – which scientists believe hasn't changed since the sun was born.

The research group at Argonne will be among the scientists to analyze the samples in an effort to better understand how the planets formed. Current measurements of the sun's composition are not precise enough to answer key questions about events in the early solar system. The researchers are also preparing to analyze samples from the Stardust mission, which recently captured dust grains from a comet's tail and will bring them back to Earth in 2006.

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The nation's first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. The University of Chicago operates Argonne as part of the U.S. Department of Energy's national laboratory system.