Nuclear states with anomalously large radius (size isomers)
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CLEI Experiment
Nuclear States with Anomalously Large Radius (Size Isomers) A. A. Ogloblin1) , A. S. Demyanova1)* , A. N. Danilov1), T. L. Belyaeva2) , S. A. Goncharov3), and W. Trzaska4) Received November 25, 2015
Abstract—Methods of determination of the nuclear excited state radii are discussed together with the recently obtained data on the states of some light nuclei having abnormally large radii (size isomers). It is shown that such states include excited neutron-halo states in 9 Ве, 11 Ве, and 13 С and some alphacluster states in 12 С, 11 В, and 13 С. Among the latter ones, there is the well-known Hoyle state in 12 С—the structure of this state exhibit rudimentary features of alpha-particle states. DOI: 10.1134/S1063778816040177
1. INTRODUCTION The radius of nuclei is one of their most fundamental and important features. Reflecting the properties of both the nucleon–nucleon interaction and nuclear matter, it plays a global role in nuclear physics, with the result that even its modest deviation from standard values may reflect drastic changes in the nuclear structure. The discovery of a neutron halo for some light nuclei lying near the nucleon drip lines [1] became a spectacular illustration of the fact that nuclei of enhanced radius may possess radically new properties. Halo nuclei (for example, 11 Ве or 11 Li) are a two-component system formed by a core and one or several valence neutrons separated from it by a distance of two to three radii of the nucleus being considered. This discovery was of great importance not only because of the first ever observation of nuclei that have anomalously large dimensions but also because of the fact that these nuclei differed from all previously known ones by the presence of a broad diffuse region consisting of neutrons exclusively. It was the halo nuclei for which the term “exotic nuclei” was initially used, but, later on, this term was extended to all nuclei lying near the nucleon drip lines. For a long time, it had been implicitly assumed that excited states of nuclei had the same dimensions 1)
National Research Center Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia. 2) ´ ´ Universidad Nacional Autonoma de Meexico, Ciudad Universitaria, Mexico City Distrito Federal 4510, Mexico. 3) Faculty of Physics, Moscow State University, Moscow, 119991 Russia. 4) ¨ ¨ Seminaarinkatu 15, 40014 JyUniversity of Jyvaaskyla a, vaskylan yliopisto, Finland. * E-mail: [email protected]
as their ground states. The discovery of a neutron halo in the ground states of some light nuclei naturally raised the question of its existence in excited states as well (the first specific prediction concerning the level at 3.09 MeV in 13 С was made in [2]). The hypothesis of an alpha-particle condensate in nuclei [3] predicted a considerable increase in the radii of nuclei in states near some thresholds for alpha-particle emission. Concurrently, it was expected that, in some individual cases, the radii of such hypothetical states may reach the dimensions of uranium nuclei [4]! The idea of an alp
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