Big computers will offer
glimpse of the very small
Posted October 25, 2011
Extreme computing can help researchers simulate incredible densities – like those resulting from collapse of the supernova depicted here. Click image to enlarge and for more information.
Part of a series.
The periodic table of the elements hanging in most chemistry classrooms has about 100 entries – and is just the first few words in the story of chemical interaction, says James Vary, professor of physics at Iowa State University.
Those entries represent only one form of each element, with a particular number of neutrons and protons, collectively known as nucleons, in the nucleus of the element’s atoms. But “the chart of the atomic nuclei – the isotopes – has thousands of entries since there are a variable number of neutrons for each chemical species,” Vary says.
Many of those thousands of nuclei are unstable and difficult to study experimentally. Nonetheless, they play crucial roles in generating nuclear energy and maintaining national security. Consequently, “we need forefront theoretical calculations to characterize” their properties, Vary says.
For example, nuclear physicists continue to search for the connection between quantum chromodynamics (QCD) – the theory of quarks and gluons – and nuclei. Although QCD is the theory for the strong interactions between particles, such as the nucleons, more work remains to understand how quarks and gluons lead to neutrons and protons or other strongly interacting particles.
“We don’t know the force among protons and neutrons well enough,” says David Dean, who directs the Physics Division at Oak Ridge National Laboratory and has been on special assignment as senior advisor to the under secretary for science at the Department of Energy (DOE). “So we work on various calculations to help us pin down what that force is and how it is acting.”
To search for this force between neutrons and protons, Dean takes a range of approaches. For example, for several years he’s worked on ab initio theories of nuclear structure – theories based on fundamental physics with few assumptions. That work included a grant from INCITE (Innovative and Novel Computational Impact on Theory and Experiment), a DOE program that awards large slices of time on high-performance computers. He’s also used INCITE time to simulate phase transitions in warm, rotating nuclei. “We are working on a paper dealing with the anomalously long lifetime of carbon-14 from an ab initio point of view,” using INCITE time to run applications at petascale – quadrillions of calculations per second.