Exploring Light Neutron-Rich Nuclei: First Observation of Oxygen-28

The neutron-rich oxygen isotopes oxygen-27 and oxygen-28 exist as very short-lived resonances, report scientists from Tokyo Tech based on the first observation of their decay into oxygen-24 and three and four neutrons, respectively. Notably, the oxygen-28 nucleus is found not to be “doubly magic” as expected in the standard shell-model picture. This study provides valuable insights into the nuclear structure.

Exploring Light Neutron-Rich Nuclei: First Observation of Oxygen-28

The study of physical systems under extreme conditions offers valuable insights into their organization and structure. In nuclear physics, neutron-rich isotopes, especially the light ones with neutron-to-proton ratio significantly different from that of stable nuclei, provide stringent tests of modern nuclear structure theories. These isotopes exist as very short-lived resonances, decaying through spontaneous neutron emission.

Now, in a new study published in available in Nature, an international collaboration of researchers led by Yosuke Kondo, an Assistant Professor at the Department of Physics at Tokyo Institute of Technology, reports the first observation of two such isotopes—oxygen-28 (28O) and oxygen-27 (27O)—through their decay into oxygen-24 with four and three neutrons, respectively. The nucleus 28O, which consists of 8 protons and 20 neutrons (N), is of significant interest as it is expected to be one of the few ‘doubly magic’ nuclei in the standard shell-model picture of nuclear structure.

The study’s success was enabled by the capabilities of the RIKEN RI Beam Factory, which could produce intense beams of unstable nuclei coupled to an active target of thick liquid hydrogen and multi-neutron detection arrays. Proton-induced nucleon knockout reactions from a high-energy 29F beam generated the neutron-unbound isotopes 27O and 28O. The researchers observed these isotopes and studied their properties by directly detecting their decay products.

They found that both 27O and 28O exist as narrow low-lying resonances and compared their decay energies to the results of sophisticated theoretical models—a large-scale shell model calculation and a newly developed statistical approach—based on effective field theories of quantum chromodynamics. Most theoretical approaches predicted higher energies for both isotopes. “Specifically, the statistical coupled-cluster calculations suggested that the energies of 27O and 28O can provide valuable constraints for the interactions considered in such ab initio approaches,” points out Dr. Kondo.

The researchers also investigated the cross-section for the production of 28O from the 29F beam, finding it to be consistent with 28O not exhibiting a closed N = 20 shell structure. “This result suggests that the ‘island of inversion,’ whereby the energy gap between neutron orbitals weakens or vanishes, extends beyond the fluorine isotopes 28F and 29F into the oxygen isotopes,” explains Dr. Kondo.

The present findings enhance our understanding of nuclear structure by offering new insights, especially for extremely neutron-rich nuclei. In addition, the detailed investigation of multi-neutron correlations and the study of other exotic systems now become possible with the multi-neutron-decay spectroscopy technique utilized here.

Let us hope that future research unravels many more mysteries surrounding nuclei!


Authors :
Y. Kondo1,2,*, N.L. Achouri3, H. Al Falou4,5, L. Atar6, T. Aumann6,7,8, H. Baba2, K. Boretzky7, C. Caesar6,7, D. Calvet9, H. Chae10, N. Chiga2, A. Corsi9, F. Delaunay3, A. Delbart9, Q. Deshayes3, Zs. Dombrádi11, C.A. Douma12, A. Ekström13, Z. Elekes11, C. Forssén13, I. Gašparić2,6,14, J.-M. Gheller9, J. Gibelin3, A. Gillibert9, G. Hagen15,16, M.N. Haraken7,12, A. Hirayama1, C.R. Hoffman17, M. Holl6,7, A. Horvat7, Á. Horváth18, J.W. Hwang19,20, T. Isobe2, W.G. Jiang13, J. Kahlbow2,6, N. Kalantar-Nayestanaki12, S. Kawase21, S. Kim19,20, K. Kisamori2, T. Kobayashi22, D. Körper7, S. Koyama23, I. Kuti11, V. Lapoux9, S. Lindberg13, F.M. Marqués3, S. Masuoka24, J. Mayer25, K. Miki22, T. Murakami26, M. Najafi12, T. Nakamura1,2, K. Nakano21, N. Nakatsuka26, T. Nilsson13, A. Obertelli9, K. Ogata27,28,29, F. de Oliveira Santos30, N.A. Orr3, H. Otsu2, T. Otsuka2,23, T. Ozaki1, V. Panin2, T. Papenbrock15,16, S. Paschalis6, A. Revel3,30, D. Rossi6, A. T. Saito1, T. Y. Saito23, M. Sasano2, H. Sato2, Y. Satou20, H. Scheit6, F. Schindler6, P. Schrock24, M. Shikata1, N. Shimizu31, Y. Shimizu2, H. Simon7, D. Sohler11, O. Sorlin30, L. Stuhl2,19, Z. H. Sun15,16, S. Takeuchi1, M. Tanaka32, M. Thoennessen33, H. Törnqvist6,7, Y. Togano1,34, T. Tomai1, J. Tscheuschner6, J. Tsubota1, N. Tsunoda24, T. Uesaka2, Y. Utsuno35, I. Vernon36, H. Wang2, Z. Yang2, M. Yasuda1, K. Yoneda2, and S. Yoshida37
Title :
First observation of 28O
Journal :
Affiliations :
1Department of Physics, Tokyo Institute of Technology, Tokyo, Japan

2RIKEN Nishina Center, Saitama, Japan

3LPC Caen UMR6534, Université de Caen Normandie, ENSICAEN, CNRS/IN2P3, Caen, France

4Lebanese University, Beirut, Lebanon

5Lebanese-French University of Technology and Applied Sciences, Deddeh, Lebanon

6Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany

7GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany

8Helmholtz Research Academy Hesse for FAIR, Darmstadt, Germany

9Irfu, CEA, Université Paris-Saclay, Gif-sur-Yvette, France

10Institute for Basic Science, Daejeon, Republic of Korea

11Atomki, Debrecen, Hungary

12ESRIG, University of Groningen, Groningen, The Netherlands

13Institutionen för Fysik, Chalmers Tekniska Högskola, Göteborg, Sweden

14Ruđer Bošković Institute, Zagreb, Croatia

15Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA

16Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, USA

17Physics Division, Argonne National Laboratory, Argonne, IL, USA

18Eötvös Loránd University, Budapest, Hungary

19Center for Exotic Nuclear Studies, Institute for Basic Science, Daejeon, Republic of Korea

20Department of Physics and Astronomy, Seoul National University, Seoul, Republic of Korea

21Department of Advanced Energy Engineering Science, Kyushu University, Fukuoka, Japan

22Department of Physics, Tohoku University, Miyagi, Japan

23Department of Physics, The University of Tokyo, Tokyo, Japan

24Center for Nuclear Study, The University of Tokyo, Saitama, Japan

25Institut für Kernphysik, Universität zu Köln, Köln, Germany

26Department of Physics, Kyoto University, Kyoto, Japan

27Department of Physics, Kyushu University, Fukuoka, Japan

28Research Center for Nuclear Physics, Osaka University, Osaka, Japan

29Department of Physics, Osaka City University, Osaka, Japan

30Grand Accélérateur National d’Ions Lourds (GANIL), CEA/DRF-CNRS/IN2P3, Caen, France

31Center for Computational Sciences, University of Tsukuba, Ibaraki, Japan

32Department of Physics, Osaka University, Osaka, Japan

33Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA

34Department of Physics, Rikkyo University, Tokyo, Japan

35Advanced Science Research Center, Japan Atomic Energy Agency, Ibaraki, Japan

36Department of Mathematical Sciences, Durham University, Durham, UK

37Liberal and General Education Center, Institute for Promotion of Higher Academic Education, Utsunomiya University, Tochigi, Japan

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