The composition of neutron star atmospheres is calculated as a function of time including effects of diffusion, cooling and thermonuclear reactions. A seven-component nuclear reaction network with includes He4, C12, O16, Ne20, Mg24, Si28 and Fe56 is utilized. Neutron star models with different initial nuclear abundances are compared as to subsequent nucleosynthesis. It is found that the final abundances are independent of original composition assuming He4 as the major initial constituent. The final composition of the atmosphere is predominantly Fe56. Mass loss from an evolving neutron star is examined as a possible source of cosmic rays. It is found that a neutron star contributes only Fe56 significantly to the cosmic-ray spectrum.