I was reading this document to understand the links between the attenuation coefficient and quantum scattering. Consider a beam of number density $\rho$ and velocity $v$ in the z direction. $I = \rho v$ satisfies the following equation
$$ \frac{dI}{dz} = -\mu I $$ where $\mu$ is the attenuation constant. The aforementioned file discusses a quantum treatment involving Fermi's golden rule, but is there a way to express $\mu$ in terms of the scattering amplitude $f$ or the differential cross section?
