“Doubly Enigmatic” – Scientists Witness Debut of Oxygen-28 for the First Instance
In a groundbreaking feat, scientists have observed the decay of the neutron-rich isotopes 28O and 27O, witnessing their transformation into oxygen-24. This observation not only imparts fresh insights into theories about nuclear structure but also suggests an extension of the ‘island of inversion’ to encompass oxygen isotopes. This advancement facilitates the exploration of intricate multi-neutron correlations and exotic systems.
The pursuit of comprehending physical systems under extreme circumstances yields invaluable revelations about their arrangement and composition. Within the realm of nuclear physics, the investigation of neutron-rich isotopes, particularly the lighter ones with an unconventional neutron-to-proton ratio compared to stable nuclei, presents rigorous tests for contemporary nuclear structure theories. These isotopes exist fleetingly, swiftly succumbing to neutron emission.
A recent study, detailed in the pages of Nature, represents a collaborative endeavor undertaken by an international assembly of researchers, helmed by Yosuke Kondo, an Assistant Professor at Tokyo Institute of Technology’s Department of Physics. This study marks the inaugural observation of two such isotopes—oxygen-28 (28O) and oxygen-27 (27O)—as they transition into oxygen-24, laden with four and three neutrons, respectively. The nucleus 28O, composed of 8 protons and 20 neutrons (N), piques interest due to its status as a prospective ‘doubly enigmatic’ nucleus within the conventional shell-model depiction of nuclear structure.
The success of this study was rendered feasible by leveraging the capabilities of the RIKEN RI Beam Factory, which could generate intense beams of unstable nuclei coupled with an active thick liquid hydrogen target and arrays for detecting multi-neutron emissions. Employing proton-induced nucleon knockout reactions from a high-energy 29F beam led to the creation of neutron-unbound isotopes 27O and 28O. Researchers effectively observed these isotopes and scrutinized their attributes by directly detecting the products of their decay.
Both the 27O and 28O isotopes, confined to narrow low-lying resonances, serve as rigorous touchstones for contemporary nuclear structure theories, thereby widening the frontiers of our knowledge. These observations align their decay energies with the outcomes projected by sophisticated theoretical models—a large-scale shell model calculation and an innovative statistical methodology—predicated on effective field theories of quantum chromodynamics. Notably, the statistical coupled-cluster calculations indicate that the energies of 27O and 28O can furnish valuable constraints for interactions evaluated in such ab initio approaches, as emphasized by Dr. Kondo.
The researchers delved into the cross-section pertaining to the production of 28O from the 29F beam and found concurrence with the idea that 28O does not demonstrate a closed N = 20 shell structure. This outcome alludes to the extension of the ‘island of inversion,’ where the energy gap among neutron orbitals wanes or disappears, beyond the fluorine isotopes 28F and 29F, encompassing the oxygen isotopes, as elucidated by Dr. Kondo.
The present revelations foster an enriched comprehension of nuclear structure, proffering novel insights, particularly concerning extremely neutron-rich nuclei. Furthermore, the comprehensive exploration of multi-neutron correlations and the study of other extraordinary systems are now within reach, thanks to the multi-neutron-decay spectroscopy technique applied here.
May the forthcoming research endeavors continue to unveil the enigmas enveloping nuclei!
Reference: “First observation of 28O” by Y. Kondo, N. L. Achouri, H. Al Falou, L. Atar, T. Aumann, H. Baba, K. Boretzky, C. Caesar, D. Calvet, H. Chae, N. Chiga, A. Corsi, F. Delaunay, A. Delbart, Q. Deshayes, Zs. Dombrádi, C. A. Douma, A. Ekström, Z. Elekes, C. Forssén, I. Gašparić, J.-M. Gheller, J. Gibelin, A. Gillibert, G. Hagen, M. N. Harakeh, A. Hirayama, C. R. Hoffman, M. Holl, A. Horvat, Á. Horváth, J. W. Hwang, T. Isobe, W. G. Jiang, J. Kahlbow, N. Kalantar-Nayestanaki, S. Kawase, S. Kim, K. Kisamori, T. Kobayashi, D. Körper, S. Koyama, I. Kuti, V. Lapoux, S. Lindberg, F. M. Marqués, S. Masuoka, J. Mayer, K. Miki, T. Murakami, M. Najafi, T. Nakamura, K. Nakano, N. Nakatsuka, T. Nilsson, A. Obertelli, K. Ogata, F. de Oliveira Santos, N. A. Orr, H. Otsu, T. Otsuka, T. Ozaki, V. Panin, T. Papenbrock, S. Paschalis, A. Revel, D. Rossi, A. T. Saito, T. Y. Saito, M. Sasano, H. Sato, Y. Satou, H. Scheit, F. Schindler, P. Schrock, M. Shikata, N. Shimizu, Y. Shimizu, H. Simon, D. Sohler, O. Sorlin, L. Stuhl, Z. H. Sun, S. Takeuchi, M. Tanaka, M. Thoennessen, H. Törnqvist, Y. Togano, T. Tomai, J. Tscheuschner, J. Tsubota, N. Tsunoda, T. Uesaka, Y. Utsuno, I. Vernon, H. Wang, Z. Yang, M. Yasuda, K. Yoneda and S. Yoshida, 30 August 2023, Nature.
DOI: 10.1038/s41586-023-06352-6
This study received funding from the Japan Society for the Promotion of Science, Deutsche Forschungsgemeinschaft, GSI-TU Darmstadt cooperation agreement, GSI, German Federal Ministry for Education and Research, European Research Council, H2020 European Research Council, Swedish Research Council, Franco-Japanese LIA-International Associated Laboratory for Nuclear Structure Problems, French ANR-14-CE33-0022-02 EXPAND, Institute for Basic Science in Korea, U.S. Department of Energy, National Science Foundation, National Supercomputer Centre, HIC for FAIR and Croatian Science Foundation, National Research, Development and Innovation Fund of Hungary, Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program, and the Swedish National Infrastructure for Computing.
Table of Contents
Frequently Asked Questions (FAQs) about nuclear structure
What is the significance of the observed decay of oxygen-28 and oxygen-27 isotopes?
The observed decay of oxygen-28 and oxygen-27 isotopes provides valuable insights into nuclear structure theories and extends the understanding of the ‘island of inversion’ concept within oxygen isotopes. These observations open avenues for studying multi-neutron correlations and exotic nuclear systems.
How were the oxygen-28 and oxygen-27 isotopes observed?
An international collaboration led by Yosuke Kondo used the RIKEN RI Beam Factory to generate intense beams of unstable nuclei. These beams interacted with a thick liquid hydrogen target and detection arrays to capture the decay of oxygen-28 and oxygen-27 isotopes into oxygen-24.
Why is oxygen-28 of particular interest?
Oxygen-28, composed of 8 protons and 20 neutrons, is intriguing due to its potential as a ‘doubly magic’ nucleus in the standard shell-model view of nuclear structure. This observation provides essential data to validate and refine theoretical models.
How do the observed isotopes challenge existing theories?
The observed decay energies of oxygen-28 and oxygen-27 were compared with theoretical predictions. The results from sophisticated theoretical models and innovative statistical approaches based on effective field theories of quantum chromodynamics yielded unexpected outcomes, challenging existing assumptions.
What does the extension of the ‘island of inversion’ concept imply?
The extension of the ‘island of inversion’ concept into oxygen isotopes suggests that the weakening or vanishing of energy gaps between neutron orbitals is not limited to fluorine isotopes. This finding deepens our understanding of nuclear structure and points toward new avenues of exploration.
How does this study advance our knowledge of nuclear structure?
This study enhances our understanding of nuclear structure by shedding light on neutron-rich nuclei under extreme conditions. The detailed investigation of decay processes and the application of multi-neutron-decay spectroscopy contribute to expanding our comprehension of these intricate systems.
More about nuclear structure
- Nature: “First observation of 28O”
- Tokyo Institute of Technology Department of Physics
- RIKEN RI Beam Factory
- Effective Field Theories of Quantum Chromodynamics
