Interplay between collective and single particle excitations around neutron-rich doubly-magic nuclei

S Leoni,V Greco,C Spitaleri,M La Cognata,S Pirrone,F Rizzo

doi:10.1051/epjconf/201611704001

S Leoni, V Greco + Show 4 more

Open Access

https://doi.org/10.1051/epjconf/201611704001

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Abstract

The excitation spectra of nuclei with one or two particles outside a doubly-magic core are expected to be dominated, at low energy, by the couplings between phonon excitations of the core and valence particles. A survey of the experimental situation is given for some nuclei lying in close proximity of neutron-rich doubly-magic systems, such as 47,49 Ca, 133 Sb and 210 Bi. Data are obtained with various types of reactions (multinucleon transfer with heavy ions, cold neutron capture and neutron induced fission of 235 U and 241 Pu targets), with the employment of complex detection systems based on HPGe arrays. A comparison with theoretical calculations is also presented, in terms of large shell model calculations and of a phenomenological particle-phonon model. In the case of 133 Sb, a new microscopic “hybrid” model is introduced: it is based on the coupling between core excitations (both collective and non-collective) of the doubly-magic core and the valence nucleon, using the Skyrme effective interaction in a consistent way.

Highlights

One of the greatest challenges of contemporary nuclear physics is the achievement of a unified microscopic description of all nuclei through the entire periodic table, on basis of the common symmetry principle of the nuclear force
Large scale Shell Model calculations can be performed for nuclei up to mass 100 and around closed shells, assuming a frozen core as a truncation scheme
One restricts excitations to valence nucleons within one/two oscillator shells, neglecting almost completely the excitations of the core. This become a relevant limitation in nuclei with one or two particles outside a doubly-magic core, since in these systems the lowest structure should be dominated by the couplings between phonon excitations of the core and valence particles, giving rise to series of multiplets [2]

Summary

Introduction

One of the greatest challenges of contemporary nuclear physics is the achievement of a unified microscopic description of all nuclei through the entire periodic table, on basis of the common symmetry principle of the nuclear. The lifetime of the 4017 keV level (depopulated by the 660-keV γ-ray) was found to be 8.5±2.0 ps, which gives a reduced transition probability B(E3) = 7.9 ± 2.0 Wu, in good agreement with the measured strength of the 3− phonon of 48Ca. A similar analysis was performed on the 47Ca reaction product and the state at 3999 keV was suggested to be the 11/2+ or 13/2+ member of the 3− ⊗ f−7/12 multiplet. A similar analysis was performed on the 47Ca reaction product and the state at 3999 keV was suggested to be the 11/2+ or 13/2+ member of the 3− ⊗ f−7/12 multiplet This identification was supported by the lifetime analysis, which provided a reduced transition probability equal to B(E3)=7.4±1.9 W.u., again very similar to the 3− phonon strength of 48Ca. A weak coupling model [2] can be applied to predict the excitation energy spectrum arising from coupling a particle/hole to a phonon. The shell model calculations can be considered rather successful in reproducing the 49Ca data, demonstrating their capability in calculating complex core excitations up into the mass A≈50 region

Around the exotic doubly-magic 132Sn: the oneproton nucleus 133Sb

Conclusions