T can be approximated by the Gamow transparency, which has the form: T ≈ ≈ e − − ϵ ϵ G / ϵ ϵ where ϵ ϵ G = ( π π α α Z 1 Z 2 ) 2 × × 2 m r c 2 is the Gamow factor and comes from estimating the quantum tunneling probability through the potential barrier.