By Amit Malewar 7 Dec, 2024
Collected at: https://www.techexplorist.com/first-precise-mass-measurements-several-exotic-atomic-nuclei/94237/
The atomic nucleus is a quantum many-body system of protons and neutrons. A “halo” refers to a rare and exotic nuclear structure in weakly bound nuclei, where one or more nucleons (usually neutrons) extend far beyond the nucleus, creating a much larger radius than typical neighboring nuclei. Neutron halos have been more commonly observed in experiments, while proton halos are much less frequent.
The Coulomb barrier, which arises from the electrostatic repulsion between the positively charged protons and the nucleus, makes it difficult for protons to form a halo. This barrier limits the ability of protons to extend beyond the nucleus.
However, with precise nuclear masses, researchers could reveal signs of the proton halo.
In collaboration with others, researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences have made significant advances by achieving the first precise mass measurements of several exotic atomic nuclei. This data allowed them to determine the proton dripline for aluminum, phosphorus, sulfur, and argon elements. Based on these findings, they proposed a new approach to detect and study proton halo structures.
The researchers experimented with the Cooler Storage Ring (CSR) at the Heavy Ion Research Facility in Lanzhou (HIRFL). Using the newly developed Bρ-defined isochronous mass spectroscopy technique, they precisely measured the masses of several exotic nuclei, including silicon-23, phosphorus-26, sulfur-27, and argon-31, for the first time.
They also improved the mass precision of sulfur-28 by a factor of 11. This high-precision data allowed them to determine the proton dripline for aluminum, phosphorus, sulfur, and argon elements. Additionally, they used the new mass measurements to extract mirror energy differences, a key physical quantity.
Associate Prof. XING Yuanming from IMP, another co-first author of this study, said, “We propose that mirror energy differences, which are solely related to atomic masses, can be used to probe proton halo structures.”
Using their new method, researchers discovered isospin symmetry breaking in certain proton-dripline nuclei, suggesting the presence of proton halo structures. Theoretical calculations supported this conclusion. The experimental results provide evidence for proton halos in nuclei such as phosphorus-26, -27, and sulfur-27, -28, and propose that argon-31 may be a new candidate for a double proton halo nucleus.
Additionally, the study found that aluminum-22 does not exhibit a proton halo. These findings offer valuable insights for future research on proton halo nuclei.
The study also demonstrated that mirror energy differences could serve as a sensitive indicator of isospin symmetry breaking and the presence of proton halo structures, advancing both experimental and theoretical research in this area.
Journal Reference:
- Y. Yu, Y. M. Xing et al. Nuclear Structure of Dripline Nuclei Elucidated through Precision Mass Measurements of 23Si, 26P,27,28S, and 31Ar. Physical Review Letters. DOI: 10.1103/PhysRevLett.133.222501
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