6-23-00
Contacts:
James Vary, Physics and Astronomy, (515) 294-8894
Skip Derra, News Service, (515) 294-4917
THEORETICAL MODEL COULD HELP DETERMINE DISCREPANCIES IN NATURE
AMES, Iowa -- A new theoretical tool, developed by a team of physicists including one from Iowa State University, could lead to a better understanding of basic physical properties of the nucleus of an atom. The work could have widespread importance and help scientists explain some of the puzzles they encounter in nature.
The team, which includes James Vary, an ISU professor of physics and astronomy and director of the International Institute for Theoretical and Applied Physics; Petr Navratil of the Lawrence Livermore National Laboratory, Livermore, Calif.; and Bruce Barrett of the University of Arizona, Tucson. They published their work in the June 19 issue of Physical Review Letters.
The paper, "Properties of Carbon 12 in the Ab Initio Nuclear Shell Model," details a theory that they have used to explain some of the mysteries physicists confront when dealing with the interactions of the particles inside the nucleus of the carbon-12 atom.
"We've taken the neutrons and the protons (the basic components of the atom's nucleus) and their elementary interactions and solved the basic properties of carbon-12," Vary said. "We have determined the binding energy, how much energy is involved in keeping it together, how it interacts with electromagnetic radiation and some of the other experimental properties of carbon 12."
The physicists' work focused on the nuclear shell model, a widely accepted model that describes of the properties of the atomic nucleus. Invented in 1949, the nuclear shell model has become a trusted method for describing nearly all the properties of the nucleus.
But the model has no underlying theory, or explanation as to why nuclei behave the way they do. The goal for decades, Vary explained, has been to develop a theory from what is observed in experiments.
The atomic nucleus is composed of neutrons and protons, which form the "superdense" material at the center of all atoms, Vary explained. The nuclear isotope called carbon 12 has six neutrons and six protons.
A shell model depicts how the particles making up the nucleus exhibit different characteristics when they are excited by an external energy source. This is similar to describing how the atomic electrons behave when a substance is heated to ever higher temperatures and emits light and other radiation in the process.
"Nobody was able to give a fundamental description of that until now," Vary said. "This work is a fundamental description of the nuclear shell model."
The "ab initio" (meaning from the beginning) model will help guide scientists as they explore some of the most exotic and enigmatic behaviors exhibited inside a nucleus.
"This creates a new tool," Vary said. "We are now able to do very precise calculations to compare with the experimental results. We will be able to explain some of the exotic behavior experimentalists encounter at the nuclear level."
For example, Vary wants to apply the "tool" to a concept called parity violations. Parity is the idea that if you do an experiment one way and obtain data, then if you do a similar, or mirror, of that experiment you should obtain a mirror copy of the data. But in parity violations this symmetry breaks down at the most minute levels -- at the subatomic scale -- resulting in dissimilar data from similar experiments. The "ab initio" tool can be used to explain why, Vary said.
Such work could lead to understanding parity violation in nature, which is intimately connected with the mystery of why we do not seem to have a universe with a balance between matter and antimatter. It also could be used to explain the seemingly enigmatic data in experiments to obtain the mass of a neutrino, which could hold a key to the mystery of dark matter, or why the universe seems to exhibit stronger gravitational effects than the observed matter would support.
In the end, Vary says this work is a technological triumph in that it pins down an explanation for the interactions inside a significant nucleus, in this case carbon 12. Other attempts to obtain "ab-initio" properties for the atomic nucleus only could handle those of up to eight particles.
The use of supercomputers (an Origin 2000 supercomputer was used for the work), and a program that can squeeze every bit of memory space and computational efficiency out of parallel processors significantly aided the effort, Vary said. And the work has wide ranging implications for fundamental research.
"The practical applications of this work is to unravel the basic secrets of nature," Vary added. "To learn why they are this way, and to pin that understanding down to a very fundamental level."
The research was supported in part by grants from the U.S. Department of Energy and the U.S. National Science Foundation.
- 30 -
RSS