The nucleus of lead atoms is wrapped in a 'shell' of neutrons: to verify its existence and measure its thickness was the Prex-II experiment, inside the Jefferson Lab in the USA, which also sees the participation of National Institute of Nuclear Physics (Infn).
The published Physical Review Letters results also help to better understand extreme astrophysical phenomena such as neutron star fusion.
Atomic nuclei are made up of protons (with a positive electric charge) and neutrons (with a neutral charge) and their number determines the properties of the atom. Heavier elements, such as lead, usually consist of a large number of neutrons, often more than protons, and until a few years ago many details of their arrangement remained unknown. "The skin of neutrons - explained Guido Maria Urciuoli, co-spokesperson of the Prex-II experiment and researcher of the Infn section of Rome - is determined by the balance between the surface tension and the difference between the values of the symmetry energy at inside and to the surface in the core. This difference is the so-called 'symmetry pressure', responsible for the displacement of neutrons towards the outside of the nucleus ”.The result of the Prex-II collaboration is also of considerable importance for astrophysics because it provides valuable information to better understand the characteristics of neutron stars, whose radius is determined precisely by the symmetry pressure, responsible for the neutron skin in lead nuclei. . The measurement of this physical quantity will also allow us to describe with greater precision also the deformations to which a neutron star is subjected due to the effect of the gravitational field induced by another star, in the melting phenomena of these celestial bodies.responsible for the neutron skin in lead nuclei. The measurement of this physical quantity will also allow us to describe with greater precision also the deformations to which a neutron star is subjected due to the effect of the gravitational field induced by another star, in the melting phenomena of these celestial bodies.responsible for the neutron skin in lead nuclei. The measurement of this physical quantity will also allow us to describe with greater precision also the deformations to which a neutron star is subjected due to the effect of the gravitational field induced by another star, in the melting phenomena of these celestial bodies.
