Note that γ is a little less than 1, so the top function is similar to an exponentially decreasing function of r except that at very small r it theoretically goes to infinity. But the value of the r γ γ − − 1 only surpasses 10 at a value of r smaller than 10 1 / ( γ γ − − 1 ) , which is a very small number (much less than the radius of a proton) unless Z is very large.