Relativistic scattering with a singular potential in the Dirac equation
  An elementary treatment of the Dirac equation in the presence of a three dimensional spherically symmetric delta potential is presented. We show how to calculate the cross section using the relativistic wave expansion method for a one delta potential and two concentric delta potentials. We compare our results with the cross section calculated in the Born approximation. 
M Loewe and S Mendizabal