Scientists Finally Uncover What Really Happens When an Atom Splits

The term “atom,” derived from Latin for “indivisible,” can be misleading. A recent simulation by U.S. theoretical physicists has provided a detailed microscopic view of how an atom splits in two, shedding light on an energetic event that has significantly impacted science and technology.

In 1938, physicists Otto Hahn, Lise Meitner, and Fritz Strassmann demonstrated that uranium nuclei could split when bombarded with neutrons, highlighting the inaccuracy of the term “indivisible.” Despite its applications in warfare, energy, medicine, and research, nuclear fission remains complex and enigmatic.

The nucleus of a heavy atom is not just a simple collection of protons and neutrons; it is a chaotic realm of quantum activity. Understanding how these nucleons behave and interact is particularly challenging during fission.

To simplify this process, researchers from Los Alamos National Laboratory and the University of Washington outline four key steps of fission:

1. In the initial 10^-14 seconds, a slow-moving neutron causes the nucleus to bulge and assume a saddle shape, resembling a tiny peanut shell.
2. Next, in a rapid phase known as saddle-to-scission, which lasts around 5×10^-21 seconds, the fragments of the fission process begin to form.
3. This is followed by scission, where the nucleus breaks apart in approximately 10^-22 seconds.
4. Finally, over about 10^-18 seconds, the fission fragments stabilize and accelerate away, releasing neutrons, gamma rays, and possibly triggering other decay processes.

Challenges in Theories of Subatomic Particle Movement and Interactions

While various theories attempt to explain the movement of subatomic particles throughout this process, experimental results often challenge existing physics assumptions or complicate the “microscopic” modeling of interactions among protons and neutrons.

Using a framework developed by UW physicist Aurel Bulgac, a new quantum many-body simulation provides the most accurate depiction of scission—the moment an atomic nucleus separates. This research involved extensive calculations on uranium-238, plutonium-240, and californium-252, utilizing the supercomputer at Oak Ridge National Laboratory.

Bulgac asserts, “This is likely the most precise theoretical description of neck rupture, achieved without assumptions or simplifications.” Unlike previous theories that relied on hypothetical scenarios, this study applies well-established equations from nuclear physics and quantum mechanics.

New Insights from Simulation Reveal Distinct Patterns in Fission Process

Surprisingly, the simulation revealed unexpected insights about the fission process. While some models suggested randomness during neck rupture, the team’s findings indicated a distinct ‘wrinkle‘ in subatomic particle density preceding scission. Additionally, the simulation showed that the proton neck completes its break before the neutron neck.

Importantly, the study confirmed debates about the release of high-energy neutrons during scission, predicting their energy, angular distribution, and escape directions. Bulgac notes, “Most experiments search for these neutrons based on the motion of fission fragments, but they often can’t distinguish scission neutrons from thermal neutrons emitted by hot fragments.”

With these predictions established, the next step is to conduct experiments to validate these findings on how the ‘indivisible’ atom splits. This research has been published in Physical Review Letters.

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