  Recent studies suggest that binary neutron star (NS-NS) mergers robustly
produce the heavy r-process nuclei above the atomic mass number A ~ 130 because
of their ejecta consisting of almost pure neutrons (electron fraction of Y_e <
0.1). However, little production of the lighter r-process nuclei (A = 90-120)
conflicts with the spectroscopic results of r-process-enhanced Galactic halo
stars. We present, for the first time, the result of nucleosynthesis
calculations based on the fully general-relativistic simulation of a NS-NS
merger with approximate neutrino transport. It is found that the bulk of the
dynamical ejecta are appreciably shock-heated and neutrino-processed, resulting
in a wide range of Y_e (= 0.09-0.45). The mass-averaged abundance distribution
of calculated nucleosynthesis yields is in reasonable agreement with the
full-mass range (A = 90-240) of the solar r-process curve. This implies, if our
model is representative of such events, that the dynamical ejecta of NS-NS
mergers can be the origin of the Galactic r-process nuclei. Our result also
shows that the radioactive heating after ~ 1 day from the merging, giving rise
to r-process-powered transient emission, is dominated by the beta-decays of
several species close to stability with precisely measured half-lives. This
implies that the total radioactive heating rate for such an event can be well
constrained within about a factor of two if the ejected material has a
solar-like r-process pattern.
