Abstract
Neutron-rich {96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.
Highlights
Neutron-rich 96;98Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility
Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections
Dramatic shape changes are often interpreted as a result of an inversion of two distinct quantum configurations of nucleons associated with different nuclear shapes
Summary
In a unified description of shape coexistence [6] for nuclei close to proton shell closures, e.g., Z 1⁄4 20 (Ca [7]), 28 (Ni [8]), and 82 (Pb-Hg [9]), spherical configurations corresponding to closed shells compete with deformed configurations resulting from multiparticle multihole excitations above the proton shell closures that interact with neutrons, which fill high-j intruder orbits. Numerous theoretical studies, using various approaches, have aimed to address shape evolution and coexistence in Sr and Zr isotopes [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28] They correctly reproduce the boundaries of the deformed region, but their predictions are mostly limited to what is available experimentally: energy spectra and ground-state properties such as masses and charge radii. This can be further investigated using a two-state mixing model, where the observed physical states jIþ1 i and jIþ2 i are expressed as linear combinations of pure prolate-deformed
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