The shape of an atomic nucleus is a fundamental property reflecting the spatial distribution of the nucleons. The nucleus ground state can be described in terms of electromagnetic quadrupole moments. Magnetic dipole and quadrupole moments are very sensitive to all types of correlations and provide important benchmarks in the studies of the nuclear potential. The nuclear shape does not only vary with proton and neutron number, but can also vary within the same nucleus, since the nucleons can occupy different orbitals polarizing the nucleus in different ways. This phenomenon is called the shape coexistence. It was studied in the case of the neutron deficient krypton isotopes through the Coulomb excitation of radioactive ions beam at the SPIRAL facility at GANIL-Caen, France. New studies will be also presented using the REX-ISOLDE facility at CERN.
