  We are investigating mass fractions on the crust of a neutron star which
would remain after one year of cooling. We use cooling curves corresponding
with various densities, or depths, of the neutron star just after its
formation. We assume the modified Urca process dominates the energy budget of
the outer layers of the star in order to calculate the temperature of the
neutron star as a function of time. Using a nuclear reaction network up to
technetium, we calculate how the distribution of nuclei quenches at various
depths of the neutron star crust. The initial results indicate that $^{28}$Si
is the lightest isotope to be optically thick on the surface after one year of
cooling.
