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## Main Question or Discussion Point

I am going over the optical theorem (specifically from Sakurai) and I just have a simple couple of questions. The optical theorem says

[tex]\sigma_{total}=\frac{4\pi}{k}\text{Im}(f(0))[/tex]

Where ##f(0)## is the scattering amplitude in the forward direction. (Which I am assuming means the direction parallel to the incident direction. Or does it mean in the direction back towards the source?)

I just want to verify what is meant by the total cross section. To me the total cross section means the amount the incoming wave function is scattered integrated in all directions over a sphere around the scatterer. Is this the correct way of thinking?

[tex]\sigma_{total}=\frac{4\pi}{k}\text{Im}(f(0))[/tex]

Where ##f(0)## is the scattering amplitude in the forward direction. (Which I am assuming means the direction parallel to the incident direction. Or does it mean in the direction back towards the source?)

I just want to verify what is meant by the total cross section. To me the total cross section means the amount the incoming wave function is scattered integrated in all directions over a sphere around the scatterer. Is this the correct way of thinking?