Synopsis: Fission Takes Its Time

Nuclear fission simulations show that the evolution of a splitting plutonium nucleus may be slower than previously thought.
Synopsis figure
A. Bulgac/University of Washington, Seattle

Harnessing the power of nuclear fission was one of the most significant breakthroughs of modern science. And yet, surprisingly, the microscopic details of the fission process are poorly understood. New numerical simulations that treat the nucleus like a superfluid capture the dynamics of a fracturing plutonium nucleus without assuming any of the conditions that other fission models have required. The results of the simulations show that the final stage of the fission process lasts 10 times longer than previously calculated.

Nuclear fission is a complex many body problem, involving over 200 nucleons packed in a highly deformed nucleus. Current modeling methods typically rely on density-functional theory (DFT), which looks at the evolution of the nuclear density, rather than particle wave functions. But to date, most DFT models of fission have only worked by imposing certain constraints, such as axial symmetry or adiabatic energy evolution.

Aurel Bulgac from the University of Washington, Seattle, and colleagues developed a more generic model of fission based on a superfluid DFT framework, in which the protons and neutrons pair up (like the electrons in a superconductor). This superfluid model gives accurate predictions for many nuclear phenomena, as shown in previous work, but this is the first time it has been applied to fission. The team’s simulations, performed on the Titan supercomputer at Oak Ridge National Lab in Tennessee, track the final stage of the process, when the two daughter nuclei rip apart. The predicted kinetic energies of the fission fragments were consistent with experimental observations. However, the fragments remained in contact longer than expected from previous theoretical estimates. The new simulations could improve models of neutron and gamma-ray emission from the fragments.

This research is published in Physical Review Letters

–Michael Schirber


More Features »


More Announcements »

Subject Areas

Nuclear Physics

Previous Synopsis

Fluid Dynamics

Whisky-Inspired Coatings

Read More »

Next Synopsis

Related Articles

Viewpoint: Watching the Hoyle State Fall Apart
Nuclear Physics

Viewpoint: Watching the Hoyle State Fall Apart

Two experiments provide the most precise picture to date of how an excited state of carbon decays into three helium nuclei. Read More »

Synopsis: Strong Force Calculations for Weak Force Reactions
Nuclear Physics

Synopsis: Strong Force Calculations for Weak Force Reactions

Theorists have used lattice-QCD calculations to predict two weak-force-driven reactions—proton fusion and tritium decay. Read More »

Synopsis: Proton Loses Weight
Particles and Fields

Synopsis: Proton Loses Weight

The most precise measurement to date of the proton mass finds a value that is 3 standard deviations lower than previous estimates. Read More »

More Articles