 When the step function is replaced with a ramp that spans some finite distance "w", the probability of reflection approaches zero in the limit formula_26, where "k" is the wavenumber of the particle.The relativistic calculation of a free particle colliding with a step potential can be obtained using relativistic quantum mechanics.For the case of 1/2 fermions, like electrons and neutrinos, the solutions of the Dirac equation for high energy barriers produce transmission and reflection coefficients that are not bounded.