Amazing stuff!
"Researchers ... have revealed how a special type of force within an atom's nucleus, known as the three-nucleon force, impacts nuclear stability. The study ... provides insight into why certain nuclei are more stable than others and may help explain astrophysical processes, such as the formation of heavy elements within stars. ...
The most powerful nuclear force is the two-nucleon force, which attracts two nucleons at long range to pull them together and repels at short range to stop the nucleons from getting too close. ...
With the three-nucleon force, there are three players, or nucleons, and balls, or mesons, are passed between them. ...
Finally, the researchers discovered another surprising effect of the three-nucleon force on nucleon spins. With only the two-nucleon force, the spin states of both nucleons can be measured individually. However, the three-nucleon force creates quantum entanglement, where two of the three nucleons have spins that exist in both states at once until measured. ..."
"... Increased stability occurs ... due to enhancing a process known as spin-orbit splitting. When nucleons spin and orbit in the same direction, the alignment of these nucleons leads to a reduction in energy. But when nucleons spin and orbit in opposing directions, these nucleons exist in a higher energy state. This means that nucleons “split” into different energy shells, providing the nucleus with a stable structure.
“Our supercomputer simulations showed that while the three-nucleon force increases the energy state of the nucleons with an aligned spin and orbit, it causes the nucleons with opposing spins and orbits to gain even more energy. This results in a larger energy gap between the shells, making the nuclei even more stable,” ...
Importantly, this effect becomes more pronounced in heavier nuclei that contain more nucleons. In the heaviest element examined—carbon-12, which has 12 nucleons—the three-nucleon force caused the energy gap to widen by a factor of 2.5. ...
The three-nucleon force could play a key role in understanding how heavy elements form from the fusion of lighter elements in stars. ..."
From the abstract:
"The three-nucleon force (3NF) is crucial in shaping the shell structure of atomic nuclei, particularly impacting the enhancement of spin-orbit (SO) splitting, especially in nuclei with significant deviations from stability. Despite its importance, the specific mechanisms driving this enhancement remain unclear.
In this study, we introduce a decomposition scheme based on the rank of irreducible tensors forming the 3NF, derived from chiral effective field theory at next-to-next-to-leading order, to elucidate their influence on SO splitting.
Within the shell-model framework, our analysis reveals that the rank-1 component of the 3NF is the primary factor enlarging the energy gap between the and single-particle levels in p-shell nuclei, while the rank-2 component makes a subdominant contribution.
Since the rank-1 component originates exclusively from the 2π-exchange 3NF, our finding will not depend on the choice of the low-energy constants of contact terms. We also remark on the antisymmetry of the rank-1 3NF, which can affect the quantum entanglement of spin states. This study lays the groundwork for further exploration into this field toward a microscopic understanding of the 3NF impact on the nuclear shell structure."
An overlooked nuclear force helps keep matter stable (original news release) "Scientists reveal that the three-nucleon force has a stronger than anticipated impact on the stability of an atom’s nucleus, with ramifications across astrophysics and quantum technology"
Fig. 2. The three-nucleon force enhances spin-orbit splitting, which causes a larger energy gap between nuclear shells and stabilizes the nucleus.
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