Study gathers strong evidence of the doubly magic nature of ¹⁰⁰Sn

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Recent experiments at CERN have shed new light on the nuclear properties of atomic nuclei (i.e., the central regions of atoms accounting for most of their mass). A key objective of recent research into atomic nuclei has been to better understand the properties of Tin-100 (¹⁰⁰Sn), a rare isotope with 50 protons and 50 neutrons.

In nuclear physics, these specific numbers of protons and neutrons are considered "magic." This essentially means an isotope would have complete proton and neutron shells in its nucleus, thus displaying a remarkably stable configuration.

Researchers at the Massachusetts Institute of Technology (MIT), the University of Manchester, CERN, KU Leuven, and other institutes recently gathered strong evidence suggesting that ¹⁰⁰Sn has a doubly magic nucleus. Their findings, published in Nature Physics, open new exciting possibilities for research aimed at testing and validating nuclear theories.

"Understanding the nuclear properties in the vicinity of ¹⁰⁰Sn, suggested to be the heaviest 'doubly magic' nucleus with proton number Z=50 equal to neutron number N=50, has been a long-standing challenge for experimental and theoretical nuclear physics," Dr. Jonas Karthein, first author of the paper, told Phys.org.

"Over the past decades, various experimental campaigns at major radioactive beam facilities around the world have been carried out to study isotopes near ¹⁰⁰Sn."

¹⁰⁰Sn and other isotopes with very short lifetimes (in the order of one second or shorter) need to be created artificially. Thus, physicists have only been able to produce them at insufficiently low rates. Due to the challenges associated with producing these isotopes, past experiments gathered conflicting and inconclusive results regarding their structure.

"Previous to our work, the experimental knowledge of the nuclear size and shape evolution approaching ¹⁰⁰Sn was lacking," said Karthein.

"With only one proton less than tin, indium isotopes (Z=49) offer an excellent laboratory to study the evolution of nuclear structure properties near ¹⁰⁰Sn. Recent developments in the production of indium isotopes at CERN, combined with our advances in highly sensitive laser spectroscopy techniques, enabled the first measurements approaching ¹⁰⁰Sn."

Over the past few years, nuclear theory has made significant strides toward describing heavy isotopes, including ¹⁰⁰Sn. By gathering substantial experimental evidence of the electromagnetic properties of ¹⁰⁰Sn, Karthein and his colleagues confirmed parts of existing theories while also setting a stringent benchmark for the future development of nuclear models.

"The recent development of the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at CERN-ISOLDE and the production of exotic indium isotopes at the facility allowed us to perform precision laser spectroscopy of the atomic energy levels of the indium atom, from which their nuclear electromagnetic properties can be extracted," explained Prof. Ronald Garcia Ruiz, a co-author of this study.

"By studying short-lived indium nuclei with increasing and decreasing numbers of neutrons from their stable counterparts, we were able to precisely study the evolution of the nuclear shape and size with the change in neutron number, from the naturally occurring ^113,115In, down to the neutron-deficient ¹⁰¹In and up to the neutron-rich ¹³¹In."

The findings gathered by the researchers strongly hint at the doubly magic nature of ¹⁰⁰Sn, which was predicted by recent nuclear theories but had not yet been conclusively demonstrated experimentally. Karthein and his colleagues also performed extensive nuclear calculations using state-of-the-art methods, which further elucidated the structure of ¹⁰⁰Sn atomic nuclei.

"Our results revealed strong evidence for the doubly magic nature of ¹⁰⁰Sn, thereby providing key experimental information to understand this key region of the nuclear chart and resolving conflicting results from spectroscopy experiments at facilities worldwide," said Karthein. "The simple structure of these nuclear systems offers an ideal system to guide our theoretical understanding of atomic nuclei."

The recent research by this team of researchers could guide new important avenues for the study of atomic nuclei. For instance, it will inform additional experiments at large and next-generation research facilities, including the U.S. Department of Energy's new Facility for Rare Isotope Beams (FRIB).

These efforts will enable the highly precise study of ¹⁰⁰Sn and neighboring isotopes, shedding further light on their nuclear properties. In addition, they will allow theoretical physicists to test existing knowledge and models of nuclei at extreme regions away from stability.

"The CRIS collaboration at CERN is also planning to extend these measurements further away from stability toward the neutron-deficient isotopes ^99,100In," added Karthein. "Recent independent mass measurements collected at CERN-ISOLDE further motivate the need to measure their nuclear electromagnetic properties."

More information: J. Karthein et al, Electromagnetic properties of indium isotopes illuminate the doubly magic character of ¹⁰⁰Sn. Nature Physics(2024). DOI: 10.1038/s41567-024-02612-y.

Journal information: Nature Physics

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