Improved WKB approximation for quantum tunneling: Application to heavy   ion fusion
  In this paper we revisit the one-dimensional tunneling problem. We consider Kemble's approximation for the transmission coefficient. We show how this approximation can be extended to above-barrier energies by performing the analytical continuation of the radial coordinate to the complex plane. We investigate the validity of this approximation by comparing their predictions for the cross section and for the barrier distribution with the corresponding quantum mechanical results. We find that the extended Kemble's approximation reproduces the results of quantum mechanics with great accuracy. 
A. J. Toubiana, L. F. Canto, and M. S. Hussein
nucl-th nucl-ex physics.atom-ph