Published: March 15, 2007

Physicists wipe away complexity for a clearer view of atomic nuclei

EAST LANSING, Mich. – Atomic nuclei have long locked away their secrets in huge data sets that tax even high-powered supercomputers.

But in a March 16 Physical Review Letters article, researchers from Michigan State and Central Michigan universities report dramatic success in stripping away this stubborn mathematical complexity.

The advance, which slashes computational time from days or weeks to minutes, may help address one of the most important questions in nuclear physics today: What is the structure of heavy atomic nuclei?

The key to the new model is correlation, the idea that some pairs of electrons are strongly linked and related. Correlations are what make it possible to rely on a modicum of data to make predictions about a complex system like a molecule, an atomic nucleus or, say, a nightly restaurant crowd.

To decide how to best use a limited supply of tables, restaurant owners don’t plan on each customer interacting with every other customer and moving freely from table to table. Rather, maitre d’s anticipate customers showing up in pairs or small groups and sticking together. This behavior is what physicists call coupled-cluster theory.

Such correlations also loom large in current theory of atomic nuclei. For several years, scientists have known that focusing on the behavior of pairs of nucleons – the generic term for protons and neutrons – goes a long way to painting an accurate picture of the entire atomic nucleus. But until now, no one had used coupled-cluster theory with heavy atomic nuclei.

Applying the theory to explain the structure of an isotope of nickel, the researchers found that coupled-cluster theory produced near identical results to an alternative brute-force computing method, which involved weeks of work by a high performance computing center to crunch through a 1 billion-variable equation. In contrast, the time spent doing coupled-cluster calculations– on a standard laptop – was often measured in minutes or even seconds.

“Sometimes it took longer to input the information than to run the calculation,” said Piotr Piecuch, one of the authors and a professor in the MSU Department of Chemistry and the MSU Department of Physics and Astronomy, and at National Superconducting Cyclotron Laboratory.

The research bodes well for next-generation nuclear science. Existing and planned accelerators around the world, promise to yield many new heavy isotopes for study. Theoretical models will need to keep pace with this expected avalanche of experimental data.

“We’re really starting to see the nucleus from a microscopic perspective,” said Piecuch. “This gives us a way to start with particles, in this case nucleons, build an equation and then solve it – and to do so in a way that is computationally efficient.”

The research is supported in part by the National Science Foundation and the Department of Energy.

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Michigan State University’s NSCL is a world-leading laboratory for rare isotope research and nuclear science education.

Michigan State University has been advancing knowledge and transforming lives through innovative teaching, research and outreach for more than 150 years. MSU is known internationally as a major public university with global reach and extraordinary impact. Its 16 degree-granting colleges attract scholars worldwide who are interested in combining education with practical problem solving.

 

 

 

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