  We perform ab initio calculations of isotope shifts for isotopes of cesium
(from A=123 to A=137) and francium (from A=207 to A=228). These calculations
start from the relativistic Hartree-Fock method and make use of several
techniques to include correlations. The field (volume) isotope shift is
calculated by means of an all-order correlation potential method and within the
singles-doubles partial triples linearized coupled-cluster approach. Many-body
perturbation theory in two different formulations is used to calculate the
specific mass shift. We discuss the strong points and shortcomings of the
different approaches and implications for parity nonconservation in atoms.
Changes in nuclear charge radii are found by comparing the present calculations
with experiment.
