WKB tunnelling exponent
= WKB tunnelling exponent
{c}
{title2=$T\simeq e^{-2S_B/\hbar}$}
For an opaque barrier between simple <turning points>, the leading <transmission probability> is $T\simeq e^{-2S_B/\hbar}$, where $S_B=\int\sqrt{2m[V(x)-E]}\,\mathrm dx$ over the forbidden interval. The exponent for <probability> is twice that for amplitude. Matching determines prefactors and the domain where this approximation applies.