# Decay of a Metastable State in WKB approximation

I'm looking at decay of metastable state (potential in figure) in WKB approximation. I discovered that the system admits an infinite set of quasi-localised modes with complex energy E, where the imaginary part is the decay width $$\Gamma$$ and gives the tunnelling probability: $$\Gamma=Im(E)=A e^{-B/\hbar}$$ where $$B=2\int_{x_2}^{x_3} \sqrt{2M(V(x)-E)}$$ To calculate the semiclassical exponent B, which value of energy E I need? Is it complex or not?