Positron tunnelling through the Coulomb barrier of superheavy nuclei

We study beams of medium-energy electrons and positrons which obey the Dira c equation and scatter from nuclei with Z > 100, At small distances the pot ential is modelled to be that of a charged sphere, A large peak is found in the probability of positron penetration to the origin for Z approximate to 184. This may be understood as an example of Klein tunnelling through the Coulomb barrier: it is the analogue of the Klein Paradox for the Coulomb po tential. (C) 2000 Published by Elsevier Science B.V. All rights reserved.