I wrote: About the matter of the Coulomb barrier -- I like your and Dave's argument > that the Coulomb barrier should be expected to work in one direction (and > this would also seem to be implied by the shell theorem). But Krane on > three or so occasions has written things that imply that the Coulomb > barrier works in two directions, suggesting that it's not just a > misinterpretation on my part. >
I think the difficulties come down to the fact that the Coulomb barrier not only provides a force against which incoming charged particles must counteract on approaching the nucleus (a classical effect). It also serves as a Faraday cage of sorts that prevents charged particles, which can be thought of as a type of RF, from "leaking" through it (a nonclassical effect). To the extent that that Faraday cage is weakened by surplus electron charge, RF (charged particles) can leak (tunnel) through it in either direction. In this understanding, the Coulomb barrier works in one direction as a center of Coulomb charge and in two directions as a Faraday cage. The analogy of a Faraday cage is meant to be illustrative and not taken too literally. Eric
