  Nuclear reaction rates in plasmas depend on the overlap (contact) probability
of the reacting ions. Path integral Monte Carlo (PIMC) calculations are used
here to determine these contact probabilities, g(0), for the one component
plasma (OCP) with emphasis on many-body quantum effects which can lead to order
of magnitude changes. An intuitive explanation for these effects is presented.
The small r behavior of g(r) for quantum systems and the relation to free
energies is then derived and compared to the path integral results. Going
beyond the uniform background approximation, electron screening effects and the
limits of the ``constant energy shift'' approximation are discussed.
Thermodynamic properties for the quantum OCP are analyzed in a final section.
