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International audience; In the region around 132Sn, the structure of even-even nuclei demonstrates diverse phenomenon including the transition between some typical quadrupole collective states. The doubly magic isotopic chain of Sn-isotopes seems to be the most interesting mass-region to be studied. Several theoretical and experimental studies have been focused in this mass region, recently [1]. The low-lying spectroscopy of these nuclei is one of the most powerful sources of information about nuclear shapes and shape transitions. Experimental/adopted B(E2↑) values for this mass-region are depicted in Fig. 1.

The electromagnetic structure of 140Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 2+ 1 state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that 140Sm shows considerable γ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region. ispartof: Acta Physica Polonica B vol:46 issue:3 pages:607-611 ispartof: location:Zakopane: POLAND status: published