  We present the first detailed and homogeneous analysis of the s-element
content in Galactic carbon stars of N-type. Abundances of Sr,Y, Zr (low-mass
s-elements, or ls) and of Ba, La, Nd, Sm and Ce (high-mass s-elements, hs) are
derived using the spectral synthesis technique from high-resolution spectra.
The N-stars analyzed are of nearly solar metallicity and show moderate
s-element enhancements, similar to those found in S stars, but smaller than
those found in the only previous similar study (Utsumi 1985), and also smaller
than those found in supergiant post-AGB stars. This is in agreement with the
present understanding of the envelope s-element enrichment in giant stars,
which is increasing along the spectral sequence M-->MS-->S-->SC-->C during the
AGB phase. We compare the observational data with recent $s$-process
nucleosynthesis models for different metallicities and stellar masses. Good
agreement is obtained between low mass AGB star models (M < 3 M_o) and
s-elements observations. In low mass AGB stars, the 13C(alpha, n)16O reaction
is the main source of neutrons for the s-process; a moderate spread, however,
must exist in the abundance of 13C that is burnt in different stars. By
combining information deriving from the detection of Tc, the infrared colours
and the theoretical relations between stellar mass, metallicity and the final
C/O ratio, we conclude that most (or maybe all) of the N-stars studied in this
work are intrinsic, thermally-pulsing AGB stars; their abundances are the
consequence of the operation of third dredge-up and are not to be ascribed to
mass transfer in binary systems.
