Atomic Nuclei Defy Expectations: From Round ‍to Pear-Shaped

Updated June‌ 01, 2025

For decades after ⁣the atomic nucleus was proposed in 1911, scientists ​believed it was spherical. Tho, research has revealed that most nuclei are not⁢ round at all. According to ⁤David Jenkins, a nuclear physicist at the University of⁣ York, a nucleus, composed of protons and neutrons, is tiny compared to the overall atom.

The nuclear shell model, introduced in 1949, posited⁣ that protons and neutrons​ occupy distinct shells, similar to electron shells. Jenkins noted that ‌nuclei exhibit collective behavior, ⁤rotating or‌ vibrating, which can ⁣be detected spectroscopically. rotation is only evident if the nucleus is deformed.

Experiments in the 1950s confirmed that nuclei come in various shapes. While about 90% resemble American footballs (prolate deformed),fewer are squashed like M&Ms ‍(oblate deformed). Jenkins said the reason for the prevalence of ⁢prolate shapes remains unknown. Some⁢ nuclei can even shift between shapes depending ⁢on thier energy state.

Pear-shaped nuclei are found in specific regions of the nuclear chart, ⁢especially around radium.Spherical nuclei are typically limited to atoms with “magic”‌ numbers of ⁢nuclear ‍particles.​ Paul Stevenson, a nuclear physicist at the University ⁤of Surrey, said quantum mechanics explains ⁤why spherical nuclei are rare.

The Schrödinger equation predicts the movement ​and position of‌ a nucleus, revealing that⁣ the basic​ solutions are ⁢not spherical. Stevenson explained that asymmetries in quantum wave-function solutions make particles more likely to point in one direction.

Jenkins emphasized that this discovery overturns previous perceptions of nuclei, leaving many questions unanswered about ⁣the​ quantum mechanics and nuclear physics involved.

“The only way that you can see evidence ​of rotation in ⁣nuclei is if the nucleus is deformed,” Jenkins said. “And people saw the nucleus has patterns of excitation known as rotational bands, so that pointed ​to the nucleus being deformed.”

What’s next

Further research aims‌ to understand why certain deformed shapes are more common and to explore the basic​ reasons behind the diverse shapes of​ atomic nuclei.