Solving a Beta Decay Puzzle

Researchers use advanced nuclear models to explain 50-year mystery surrounding the process stars use to transform elements.

Abstract of blue and red particles with black background leaving a comet like trail — Image courtesy of Andy Sproles, Oak Ridge National Laboratory

The Science

In the stars above, tin turns into a rare and valuable element called indium. This and other transformations occur via beta decay. Recently, a team solved that 50-year-old puzzle to explain why beta decays of atomic nuclei are slower than what’s expected based on the beta decays of free neutrons. To solve the puzzle, the team simulated tin-100 decaying into indium-100, a neighboring element on the Periodic Table by developing novel methods and using tens of millions of CPU hours on the supercomputer Titan.

The Impact

The findings fill a long-standing gap in physicists’ understanding of beta decay. This decay is an important process that impacts nucleosynthesis in core-collapse supernovae and neutron star mergers. Also, the findings emphasize the need to include subtle effects—or more realistic physics—when predicting certain nuclear processes. The achievement gives nuclear physicists increased confidence as they search for answers to some of the most perplexing mysteries related to the formation of matter in the universe. Those mysteries include neutrinoless double beta decay, which could change our view of the universe.

Summary

For decades, scientists have lacked a first-principles understanding of nuclear beta decay, in which protons convert into neutrons, or vice versa, to form other elements. Calculating beta decay precisely required the Oak Ridge National Laboratory-led team to accurately simulate the structure of the mother and daughter nuclei. They also had to account for interactions between two nucleons during the decay. This presented an extreme computational challenge. In solving it, they demonstrated that theoretical models and computation have progressed far enough to calculate some structure and decay properties with enough precision to let scientists compare theory-based and laboratory-based results. In addition to tin-100, the team performed a comprehensive study of beta decays in light to medium-heavy nuclei. These calculations confirmed that the accurate description of beta decay requires the inclusion of strong correlations in the nucleus and the coupling of beta decay to two nucleons.

Contact

Gaute Hagen
Oak Ridge National Laboratory
[email protected]

Funding

This research was supported by the Department of Energy Office of Science Nuclear Physics and Advanced Scientific Computing Research. Calculations were performed using the Oak Ridge Leadership Computing Facility’s Titan supercomputer. Additional support was provided by Lawrence Livermore National Laboratory, the National Research Council of Canada, and the Laboratory Directed Research and Development effort at Oak Ridge National Laboratory.

Publications

P. Gysbers, G. Hagen, J.D. Holt, G.R. Jansen, T.D. Morris, P. Navrátil, T. Papenbrock, S. Quaglioni, A. Schwenk, S.R. Stroberg, and K.A. Wendt, “Discrepancy between experimental and theoretical β-decay rates resolved from first principles.” Nature Physics (2019). [DOI: 10.1038/s41567-019-0450-7]