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Nouvelles perspectives sur le mécanisme de la fission nucléaire


Nouvelles perspectives sur le mécanisme de la fission nucléaire

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Les fragments issus de la fission acquièrent un mouvement de rotation sur eux même, le spin tandisque le noyau parent n’en avait pas. / Design © Birdeesign / Luc Petizon

La collaboration internationale nu-Ball, travaillant sur l’installation ALTO du laboratoire IJCLab, apporte de nouveaux résultats éclairant la manière dont les fragments de fission d’un noyau atomique acquièrent spontanément un mouvement de rotation sur eux même : le moment angulaire.

Cette étude à laquelle le CENBG est associés à 5 laboratoires de l’ IN2P3, fait l’objet d’une publication ce jour dans la revue Nature.

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New insights into the mechanism of nuclear fission Nuclear physicists at CENBG have contributed to an international research collaboration to show the way the spin of the two fragments, resulting from the splitting of an atomic nucleus, is generated / publication in Nature A series of experiments at the ALTO particle accelerator facility at IJC Laboratory in Orsay, France, has revealed that the fragments resulting from nuclear fission obtain their intrinsic angular momentum (or spin) after fission, not before, as is widely assumed. This result was made possible by the ‘nu-ball’ collaboration, an international group of nuclear physicists aiming to study a wide range of nuclei and their structure.

The main author of the study, Dr Jonathan Wilson from the IJC Laboratory in Orsay, said : ‘What really surprised me was the lack of significant dependence of the average spin observed in one fragment on the minimum spin demanded in the partner fragment. Most theories hypothesizing that spin is generated before fission would have predicted a strong correlation. Our results show that the fragment spin emerges after the splitting. It can be illustrated with by the snapping of a stretched elastic band which results in a turning force, or torque.’ The Collaboration includes researchers from 37 institutes and 16 countries – among them scientists from the CENBG. The results are presented in the newly-published article ‘Angular momentum generation in nuclear fission’ in Nature.

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Horizontal view of the ν-ball device. © Andrey Blazhev

To reveal the mechanism generating fragment spin, the team induced nuclear fission reactions at the ALTO facility and measured gamma rays, which are emitted in the process. Specifically, they irradiated samples of the uranium isotope 238U and the thorium isotope 232Th with a pulsed neutron beam. The experiments were performed from February until June 2018 with more than 1200 hours of beamtime at the particle accelerator. From CENBG Dr Teresa Kurtukian-Nieto participated in the measurements of the experiment and contributed to the scientific discussion. These new insights into the role of angular momentum in nuclear fission are important for the fundamental understanding and theoretical description of the fission process. Moreover, this finding has consequences for other research areas, such as nuclear astrophysics, the structure of neutron-rich isotopes and their role in nucleosynthesis in stars. Also there are implications for practical applications such as the gamma-ray heating problem in nuclear reactors. All these topics are being study by different researchers at CENBG and will continue to be studied in the future, gaining new ground within the framework of the CNRS International Research Network ASTRANUCAP and the ORIGINS project at the University of Bordeaux.

Publication : J.N. Wilson et al., ‘Angular momentum generation in nuclear fission’, Nature 590, 566–570 (2021). https://doi.org/10.1038/s41586-021-...

contact CENBG : Teresa Kurtukian Nieto