  Assuming a~simple spherical relativistic mean field model of the nucleus, we
estimate the width of the antiproton--neutron annihilation ($\Gamma_n$) and the
width of antiproton--proton ($\Gamma_p$) annihilation, in an antiprotonic atom
system. This allows us to determine the halo factor $f$, which is then
discussed in the context of experimental data obtained in measurements recently
done on LEAR utility at CERN. Another quantity which characterizes the
deviation of the average nuclear densities ratio from the corresponding ratio
of the homogeneous densities is introduced too. It was shown that it is also a
good indicator of the neutron halo. The results are compared to experimental
data as well as to the data of the simple liquid droplet model of the nuclear
densities. The single particle structure of the nuclear density tail is
discusssed also.
