The Relativistic Hartree Bogoliubov (RHB) model is applied in the
self-consistent mean-field approximation to the description of the neutron halo
in the mass region above the s-d shell. Pairing correlations and the coupling
to particle continuum states are described by finite range two-body forces.
Finite element methods are used in the coordinate space discretization of the
coupled system of Dirac-Hartree-Bogoliubov integro-differential eigenvalue
equations, and Klein-Gordon equations for the meson fields. Calculations are
performed for the isotopic chains of Ne and C nuclei. We find evidence for the
occurrence of neutron halo in heavier Ne isotopes. The properties of the 1f-2p
orbitals near the Fermi level and the neutron pairing interaction play a
crucial role in the formation of the halo. Our calculations display no evidence
for the neutron halo phenomenon in C isotopes.Comment: 7 pages, Latex, 5 P.S. Figures, To appear in Phys. Rev. Let
