Physicists have discovered a proton halo around new atomic nuclei.

Researchers from the Institute of Modern Physics at the Chinese Academy of Sciences (IMP), in collaboration with colleagues from Japan, Germany, and Italy, have conducted precise measurements of the masses of several exotic atomic nuclei for the first time. The data obtained enabled them to establish the proton drip line for aluminum, phosphorus, sulfur, and argon, as well as to propose a new method for studying proton halo structures.

2024-12-09 10:01:07https://naked-science.ru/article/physics/proton-halo-nuclei-mass

The atomic nucleus is the central part of an atom, a system composed of protons and neutrons. A halo is a feature of the organization of the atomic nucleus, where one or more protons or neutrons are so loosely bound to the nucleus that they exist at a considerable distance from the center, forming a kind of "cloud." The radius of such nuclei significantly exceeds the radii of nuclei with similar proton-neutron compositions.

Scientists typically observe halos in loosely bound nuclei located near the drip line — the boundary of nuclear stability, beyond which protons can no longer be held in the nucleus and "leak" out.

Researchers can more frequently observe neutron halos than proton halos, as the proton variant occurs less often due to the Coulomb repulsion between positively charged protons.

An international team of researchers has, for the first time, measured the masses of exotic isotopes of silicon, phosphorus, sulfur, and argon — ²³Si, ²⁶P, ^27,28S, and ³¹Ar. The scientists used the isochronous mass spectrometry method (Bρ-defined IMS), which measures the masses of nuclei through time and the trajectory of the nucleus's flight in a magnetic storage ring. They significantly improved the accuracy of the mass measurement for sulfur-28 by a factor of 11. The collected data allowed them to refine the position of the proton drip line for aluminum, phosphorus, sulfur, and argon.

Based on the mass measurements, the researchers derived a physical quantity — the energy differences of mirror nuclei (mirror energy differences). This could become a widely used indicator of the existence of proton halos. Additionally, the experimental results demonstrated violations of isospin symmetry in nuclei close to the proton drip line. Theoretical calculations confirmed that this is related to the existence of proton halos.

The study confirmed the presence of proton halos in phosphorus-26, phosphorus-27, sulfur-27, and sulfur-28 nuclei, and also suggested that argon-31 could be a new nucleus with a double proton halo. At the same time, it was established that the ground state of aluminum-22 does not have a halo structure. The work has been published in Physical Review Letters.

These findings will aid in the further study of exotic nuclei and deepen the understanding of processes occurring in unstable nuclei. The authors propose that the energy differences of mirror nuclei could serve as a sensitive indicator for detecting violations of isospin symmetry and identifying proton halo structures.