Measurements of a ‘Double Magic’ Atom Uncover an Unexpected Discovery

A groundbreaking experiment smashing special lead atoms with high-speed particles has revealed an unexpected twist in nuclear physics.

Physicists from the University of Surrey expected lead-208 (208Pb) to have a perfectly spherical nucleus. Instead, their findings showed a slightly flattened shape, challenging long-held assumptions about atomic structure.

A Puzzle at the Heart of Nuclear Physics

208Pb is considered “doubly magic” because it has 82 protons and 126 neutrons—both magic numbers, where nucleons form complete shells. This stability makes it the heaviest known stable isotope and a key reference for nuclear physics.

Given its stability, scientists assumed its nucleus would be a perfect sphere. However, using the GRETINA gamma-ray spectrometer at Argonne National Laboratory, researchers found evidence of a subtle deformation.

“We combined four separate measurements using the most sensitive equipment available, allowing us to make this challenging observation,” said study co-author Mark Henderson. “What we found was surprising—lead-208 is not spherical, contradicting nuclear theory.”

To investigate its shape, researchers bombarded 208Pb nuclei with particles traveling at 10% of the speed of light—roughly 30,000 kilometers per second (19,000 miles per second). These collisions excited the nucleus, enabling scientists to analyze its quantum states and determine its geometry.

The results revealed that 208Pb has a slightly oblate shape, meaning it is subtly compressed rather than perfectly round. Given how extensively this isotope has been studied, this discovery is both surprising and thought-provoking.

Rethinking Atomic Nuclei

This finding suggests that atomic nuclei may behave in more complex ways than previously thought. Scientists are now exploring possible explanations, including irregular vibrations when the nucleus is excited.

“These experiments challenge our understanding of nuclear structure,” said Paul Stevenson, a nuclear physicist at the University of Surrey. “We are refining our theories to determine whether these unexpected deformations stem from nuclear vibrations or another hidden factor.”

This discovery not only reshapes our understanding of 208Pb but also opens new avenues for studying heavy elements and nuclear stability.

Read Original Article: Science Alert

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