Proton Halos

 

The first precise mass measurements of several exotic atomic nuclei has been achieved. A team of scientists at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences has published in  Physical Review Letters on November 27.

Using the mass data they have proposed a new approach to uncover halo structures. They have also uncovered a proton drip line for aluminum, sulfur, phosphorus, and argon elements. 

The atomic nucleus is described as a quantum many-body system made up of protons and neutrons. Typically, they are the same size as a neighbor nuclei. A halo is found in a weakly bonded nuclei. It is an exotic nuclear structure that has one or more valance nucleons that show spatial distribution. Because of this spacing it has a radius larger than that of a neighbor nuclei.

Neutron halos are frequently observed, however proton halos are rare.

YuYue is a Ph.D. student from IMP. He is first co-author of this study. He reports, "It is challenging to experimentally observe proton halo nuclei, because the Coulomb barrier restricts the formation of proton halo structures. However, with the aid of precise nuclear masses, we could reveal signs of the proton halo."

Using the newly discovered masses, researchers observed a physical quality called mirror energy difference. 

Xing Yuanming is from IMP. He is another co-first author of the study. He reports on mirror energies. "We propose that mirror energy differences, which are solely related to atomic masses, can be used to probe proton halo structures."

Researchers used theoretical calculations to find isospin symmetry in some proton-drip line nuclei. The research supports evidence that proton halos exist in phosphorus-26,27 and sulfur-27,28. 

This study proves that mirror energy difference can be used as an indicator for finding isospin symmetry.