[Liaison covalente des états moléculaires dans les isotopes de Béryllium et de Carbone]
Nuclear clustering in N=Z nuclei has been studied since many decades. States close to the decay thresholds, as described by the Ikeda diagram, are of particular interest. Recent studies in loosely bound systems, as observed with neutron-rich nuclei has revived the interest in cluster structures in nuclei, with additional valence neutrons, which give rise to pronounced covalent molecular structures. The Beryllium isotopes represent the first example of such unique states in nuclear physics with extreme deformations. In the deformed shell model these are referred to as super- and hyper-deformation. These states can be described explicitly by molecular concepts, with neutrons in covalent binding orbits. Examples of recent experiments performed at the HMI-Berlin demonstrating the molecular structure of the rotational bands in Beryllium isotopes are presented. Further work on chain states (nuclear polymers) in the carbon isotopes is in progress, these are the first examples of deformed structures in nuclei with an axis ratio of 3:1. A threshold diagram with clusters bound via neutrons in covalent molecular configurations can be established, which can serve as a guideline for future work.
L'apparission d'agrégats dans les noyaux N=Z est discutée depuis longtemps. Les états dont l'énergie est proche de l'ouverture d'un canal de décroissance en fragments, comme le décrit le diagramme d'Ikeda sont particulièrement interessants. Les études récentes sur les noyaux faiblement liés, riches en neutrons par exemple, a remis au goût du jour les agrégats dans les noyaux avec un phénomène nouveau : l'apparition de structures moléculaires covalentes stabilisées par la présence de neutrons de valence. Les isotopes de Béryllium représentent le premier exemple de tel états avec une déformation extrême en physique nucléaire. Dans le cadre du modèle en couche déformé ces états correspondent aux états super- ou même hyper-deformés. Des exemples d'expériences récentes faites au HMI de Berlin montrent la structure moléculaire des bandes rotationnelles des isotopes de Béryllium. D'autres travaux cherchant à mêttre en évidence des polymères nucléaires dans les isotopes de Carbone (des chaînes d'α) sont en cours, ce serait la première observation de noyaux hyper déformés, i.e. des élipsoides allongé possédant un rapport d'axe de 3:1. Un diagramme présentant les seuils de fragmentation des agrégats liés par des neutrons de valence est proposé pour guider les travaux futurs.
Mots-clés : Noyaux riches en neutrons, Agrégats des neutrons et molécules
Wolfram von Oertzen 1, 2 ; Hans-Gerhard Bohlen 1
@article{CRPHYS_2003__4_4-5_465_0,
author = {Wolfram von Oertzen and Hans-Gerhard Bohlen},
title = {Covalently bound molecular states in beryllium and carbon isotopes},
journal = {Comptes Rendus. Physique},
pages = {465--474},
publisher = {Elsevier},
volume = {4},
number = {4-5},
year = {2003},
doi = {10.1016/S1631-0705(03)00052-5},
language = {en},
}
Wolfram von Oertzen; Hans-Gerhard Bohlen. Covalently bound molecular states in beryllium and carbon isotopes. Comptes Rendus. Physique, Volume 4 (2003) no. 4-5, pp. 465-474. doi : 10.1016/S1631-0705(03)00052-5. https://comptes-rendus.academie-sciences.fr/physique/articles/10.1016/S1631-0705(03)00052-5/
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