Researchers from the University of Kyusu in Japan have discovered a special power within the atomic nucleus known as three-nuclear interaction that significantly impacts nuclear stability. The findings, published in the journal Physics Letters B, shed light on why some nuclei are more stable than others and can offer insights into the formation of heavy elements in stars.
The atomic nucleus, which consists of protons and neutrons (nucleons), is held together by nuclear forces. The strongest force is the two-particle force, which attracts nucleons over long distances and repels them at shorter distances to prevent them from getting too close. However, the three-nuclear interaction involving three nucleons simultaneously has been less understood.
The researchers analogize nuclear forces to a game of ball. In the two-nuclear interaction, two players (nucleons) pass a ball (meson) to each other, with the lighter one, the pion, responsible for the attraction. In the three-nuclear interaction, three nucleons pass the ball among themselves while rotating and moving inside the nucleus.
While previously thought to play a minor role, recent studies reveal that the three-nuclear interaction has a significant impact on nuclear stability. Through supercomputer simulations, the scientists demonstrated that the exchange of pions between three nucleons limits their movement and rotation, resulting in only four possible combinations. One of these combinations, known as the RANG-1, plays a crucial role in stabilizing the nucleus.
The stability of nuclei is enhanced by strengthening the mechanism called spin-orbit splitting. When nucleons rotate and move in the same direction, their energy decreases, while moving in opposite directions leads to higher energy states, creating a stable nucleus structure.
Modeling showed that the three-nuclear force increases the energy level gap, making the nucleus more stable, especially in heavy elements. For instance, in carbon-12, comprised of 12 nucleons, the energy level difference increased by 2.5 times. The researchers suggest that this effect will be even more pronounced in heavier elements.
Besides influencing nuclear stability, the three-nuclear interaction can help explain processes in stellar nucleosynthesis. The stronger this force, the harder it is to capture new neutrons for the synthesis of heavier elements. Additionally, when a nucleus contains a “magic” number of protons or neutrons (completely filled shells), it becomes highly stable, complicating further fusion processes.
Furthermore, the researchers found that the three-nuclear interaction leads to quantum entanglement, where two of the three nucleons’ spins are in superposition before measurement. While similar effects have been