Can two neutrons combine

How neutrons and protons combine to form atomic nuclei


Atomic nuclei are the substance on which our existence is based. They are made up of positively charged protons and uncharged neutrons. But what happens when these combine to form cores? This question has preoccupied generations of physicists.

How exactly the neutrons are arranged in the nucleus differs depending on the atom: In some atoms the nuclei are made up of so-called clusters. These are groups of two protons and two neutrons, which are also known as alpha particles. In contrast, these alpha particles cannot be observed in other atoms. "We don't yet know why that is the case," explains Prof. Dr. Ulf Meißner from the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn.

In order to trace the processes involved in the formation of atomic nuclei more precisely, physicists today use computer simulations. However, these require extremely complex calculations. Even with the fastest supercomputers, only the formation of very small cores can be simulated today. The aim of the current study was originally to make the calculation process more efficient in order to be able to simulate the bonding relationships in larger cores in the medium term.

Unexpected observation

When two alpha particles come together in an atomic nucleus, both influence each other - they interact with each other. If the relative position of the protons and neutrons in the two alpha particles does not change, this interaction is called "local". Otherwise one speaks of a non-local interaction. "In our simulations, we varied the 'mixing ratio' between local and non-local interactions," explains Prof. Meißner. "So we added more and more local interactions."

This showed an unexpected effect: from a certain mixing ratio, the condition of the core changed fundamentally. Figuratively speaking, the core went from a gaseous to a liquid state. In the gaseous state, the core is made up of alpha particles, similar to a Bose-Einstein gas, but not in the liquid state. "The mixing ratio at which this phase transition takes place depends on the size of the core," says the first author of the study, Prof. Meißner's colleague Dr. Serdar Elhatisari.

In nature, the bonding relationships in the core are therefore very close to an instability that was not observed before, adds Prof. Meißner: "If you vary the parameter that determines the relative strength of the local to the non-local interaction just a little bit , then our universe looks completely different. Our simulations offer a completely new tool to better understand the connection between core structure and core forces. "

»Original publication

Source: University of Bonn

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