Nuclear reactions and screened-coulomb fusion rates

We discuss properties of nuclear reactions (branching ratios, reaction constants, etc.) between hydrogen isotopes from the standpoint of recent R-matrix calculation.. Using R-matrix theory to include nuclear effects at small distances, we then develop a general expression for fusion rates in complex systems that, in principle, allows a more complex interplay of the short-ranged (nuclear) and long-ranged (screened Coulomb) forces than does the familiar separable form. Calculations using the latest nuclear R-matrix information in this more correct formulation appear to agree with the separable approximation for screened Coulomb potentials of the Hulthén form, however. They indicate that fusion rates of the order of 10⁻²⁴s⁻¹ require unreasonably large electron densities if they are to result from screening in the lattice, and are more likely to arise from non-equilibrium processes producing particles with relative energies greater than 100 eV.