Study of cluster structures in nuclei through the ratio method
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Regular Article - Theoretical Physics
Study of cluster structures in nuclei through the ratio method A tribute to Mahir Hussein Pierre Capel1,2,a
, Ronald C. Johnson3,b
, Filomena M. Nunes4,c
1
Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany Physique Nucléaire et Physique Quantique (CP 229), Université libre de Bruxelles (ULB), 1050 Brussels, Belgium 3 Department of Physics, University of Surrey, Guildford GU2 7XH, UK 4 National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
2
Received: 26 September 2020 / Accepted: 19 November 2020 © The Author(s) 2020 Communicated by Nicolas Alamanos
Abstract For one-neutron halo nuclei, the cross sections for elastic scattering and breakup at intermediate energy exhibit similar angular dependences. The Recoil Excitation and Breakup (REB) model of reactions elegantly explains this feature. It also leads to the idea of a new reaction observable to study the structure of loosely-bound nuclear systems: the Ratio. This observable consists of the ratio of angular distributions for different reaction channels, viz. elastic scattering and breakup, which cancels most of the dependence on the reaction mechanism; in particular it is insensitive to the choice of optical potentials that simulate the projectiletarget interaction. This new observable is very sensitive to the structure of the projectile. In this article, we review a series of previous papers, which have introduced the Ratio Method and its extension to low beam energies and protonhalo nuclei.
1 Introduction Since their development in the mid-80s, Radioactive-Ion Beams (RIBs) have provided a unique way to explore the nuclear chart away from stability. This technical breakthrough has led to the discovery of unexpected structures. In particular, some nuclei close to the neutron dripline have been found to exhibit a matter radius much larger than their isobars [1], which contradicts the usual description of the nucleus as a tight pileup of nucleons. Further analyses have shown that this unusually large size is due to the loose binding of one or two valence nucleons, which can then exhibit a e-mail:
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a high probability of presence at a large distance from the other nucleons. Such nuclei are usually seen as a compact core, which contains most of the nucleons, around which one or two neutrons form a sort of diffuse halo [2], hence their name: halo nuclei [3]. The best known halo nuclei are 11 Be, with a one-neutron halo structure, and 11 Li, which is a twoneutron halo nucleus. On the proton-rich side of the nuclear chart, proton halos are also possible, though less probable. For example, 8 B exhibits a one-proton halo. Being located far from the bottom of the valley of stability, halo nuclei exhibit very short lifetimes, which make them difficult to study. Often reactions are
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