  The study of the hyperfine anomaly of neutron rich nuclei, in particular,
neutron halo nuclei, can give a very specific and unique way to measure their
neutron distribution and confirm a halo structure. The hyperfine structure
anomaly in Be+ ions is calculated with a realistic electronic wave function,
obtained as a solution of the Dirac equation. In the calculations, the Coulomb
potential modified by the charge distribution of the clustered nucleus and
three electrons in the 1s^2 2s configuration is used. The nuclear wave function
is obtained in the core+nucleon model of 9,11Be. The aim of this study is to
test whether the hyperfine structure anomaly reflects a halo structure in 11Be.
