Neutron-rich nuclei of mass A = 100 - 110 are of great interest for the study of nuclear
structure far from stability. Previous experimental and theoretical studies suggest a complex
evolution of deformation and collectivity in the isotopic chains of Zr, Mo, Ru and Pd. In order
to extend information on the evolution of the collectivity towards higher spin states and more
neutron-rich nuclei, lifetimes of excited states were measured in nuclei produced through a
fusion-fission reaction in inverse kinematic at GANIL. Fission fragments were separated and
identified in both A and Z with the high acceptance magnetic spectrometer VAMOS while the
EXOGAM germanium detectors array was used for the coincident g-ray detection. Lifetimes of
about twenty excited states were extracted using the plunger device of Cologne. This is the first
RDDS measurement on fission fragments which are identified in A and Z on an event-by-event
basis.
The study of this mass region is completed by theoretical calculations using self consistent
mean field and beyond mean field methods implemented with the Gogny force (D1S). The structure
of the ground states and the excited states is described with Hartree-Fock-Bogoliubov calculations
with constraints placed on the axial and triaxial deformations. Individual excitations
are investigated through blocking calculations and the high spin states are studied through cranking
calculations. Finally, an approximated generator coordinate method (GCM+GOA) using
the 5DCH hamiltonian is used to describe the low energy collective states and to interpret the
experimental evolution of the collectivity.