Winter 2002 -- vol. 20, no. 1 logos home page Contact the logos editor Argonne home page Feature articles Fermi facts, fables: Colleagues and friends share memories Researchers reach to the skies to reveal the secrets of the stars Passively safe reactors rely on nature to keep them cool Sidebar: What is a fast reactor? Enhanced IPNS to train Spallation Neutron Source user community Argonne Update Early Argonne reactor lit future of nuclear power industry Four Argonne materials scientists among world's most cited

Researchers reach to the skies
to reveal the secrets of the stars

by Steve Koppes

To reach for the stars is no mere figure of speech for scientists at Argonne National Laboratory and the University of Chicago. For them, it is the literal truth.

Using an instrument available only at Argonne, they study microscopic interstellar dust grains that meteorites have transported to Earth. Exploding stars launched these dust grains into space billions of years ago. The grains then got mixed into clouds of interstellar dust that collapsed to form the sun, the planets and meteorites. These grains now reveal details about how stars evolved over billions of years to produce the elements needed to form the Earth and all other objects in the solar system.

University of Chicago researcher Roy Lewis (right), pictured with Andrew Davis, pioneered the meteorite grain-separating technique.

"These grains are pieces of stuff that came from individual stars," said Argonne chemist Michael Pellin of Argonne's Materials Science Division. "The neat thing in studying these materials is that each one is its own record, its own story of one star."

The stories all tell the tale of nucleosynthesis, the process by which the universe creates the elements, including iron, gold and silver. But some of the grains tell a story that no one has heard before.

"We've found a new kind of heavy-element nucleosynthesis, which we think will tell us quite a bit about what's going on in supernovae as they explode," said Andrew Davis, a senior scientist in the Department of Geophysical Sciences and the Enrico Fermi Institute at the university.

After the Big Bang

Michael Pellin investigates a new type of nucleosynthesis with his University of Chicago colleagues.

After the Big Bang occurred about 14 billion years ago, the universe contained only two elements: hydrogen and helium. Atoms of hydrogen, helium and other light elements fused in the first stars to form elements such as carbon, oxygen and nitrogen, which are essential to life. Exploding stars and dying stars called red giants make elements heavier than iron by adding subatomic particles called neutrons to lighter elements.

"It isn't a terribly efficient process, which is why most of those elements are rare in nature," Davis said.

"Why is gold precious?" Pellin asked. "Well, it's hard to make in stars."

In a collaboration that spans more than a decade, the Argonne-Chicago team has focused its attention on measuring the isotopes of heavy elements in interstellar grains. Isotopes are varieties of an element that differ only in the number of neutrons at their core. They are like fingerprints left behind by certain kinds of stars, Davis said. And Argonne is the only laboratory in the world that can identify these fingerprints, using a technique called resonance ionization mass spectrometry.

"The resonant ionization technique is in fact the only one that allows enough sensitivity to be able to measure the elements to a tenth of a part per billion," said Roy Lewis, a senior scientist at the university's Fermi Institute.