Pear-Shaped Atomic Nuclei Offer Clues Into Nature Of Matter

Brett Smith for redOrbit.com – Your Universe Online

According to a study in the journal Nature, a team of international scientists has found the first ever direct evidence of pear-shaped atomic nuclei.

Bizarre pear-shaped nuclei could be the key to understanding one of the great mysteries of the universe: the reason for the Big Bang’s creation of a massive imbalance between matter and antimatter.

“If equal amounts of matter and antimatter were created at the Big Bang, everything would have annihilated, and there would be no galaxies, stars, planets or people,” said study co-author Tim Chupp, a University of Michigan professor of physics and biomedical engineering.

The reason behind the imbalance is one of physics’ great mysteries and is not accounted for in the Standard Model of particle physics that describes the basic nature of matter and the universe. It describes four basic forces that dictate how matter behaves: gravity, electromagnetic forces, “strong” interactions and “weak” interactions. These forces explain everything from behaviors within in the cores of atoms to larger-scale electrical interactions.

To explain the matter-antimatter challenge to the Standard Model theory, physicists have been searching for signs of a new type of force or interaction. A new force might be revealed by measuring how the nuclear axis of radioactive elements like radon and radium line up with their spin, physicists have theorized.

The researchers in the new study decided to focus on pear-shaped nuclei because their unusually asymmetrical shape would make the effects of the new force much easier and stronger to detect.

“The new interaction, whose effects we are studying does two things,” Chupp explained. “It produces the matter/antimatter asymmetry in the early universe and it aligns the direction of the spin and the charge axis in these pear-shaped nuclei.”

These nuclei get their shape from positive protons that are nudged out from the center of the nucleus by asymmetrical nuclear forces, which are unlike spherically symmetric forces like gravity.

“The new interaction, whose effects we are studying does two things,” Chupp said. “It produces the matter/antimatter asymmetry in the early universe and it aligns the direction of the spin and the charge axis in these pear-shaped nuclei.”

To determine the shape of the nuclei, the researchers accelerated radium and radon atoms and smashed them into tin, nickel and cadmium at CERN’s Isotope Separator facility (ISOLDE). However, because the positively charged nuclei repelled each other, nuclear reactions were not possible. The result was the excitation of the nuclei to higher energy levels and the production of gamma rays. The pattern of gamma radiation revealed the pear shape of the nucleus to the researchers.

“In the very biggest picture, we’re trying to understand everything we’ve observed directly and also indirectly, and how it is that we happen to be here,” Chupp said.

“Our findings contradict some nuclear theories and will help refine others,” said lead researcher Peter Butler, a physicist at the University of Liverpool.

Butler added that the study’s results will direct the various searches for atomic electric dipole moments (EDM) that are currently being conducted in labs across North America and Europe.

“Our expectation is that the data from our nuclear physics experiments can be combined with the results from atomic trapping experiments measuring EDMs to make the most stringent tests of the Standard Model, the best theory we have for understanding the nature of the building blocks of the universe,” Butler said.

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