This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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In TEM analysis, the probability of an incident electron interacting with an atom as it penetrates through a specimen can be given in terms of scattering "cross section" (σ) and "mean free path" λ. The cross section, when divided by the actual area of an atom, represents the probability that a scattering event will occur. For the simplified case with specimen thickness t, which consists of N atoms/unit volume, and where other effects (e.g. electron cloud screening) are ignored, the total probability of scattering an electron as it penetrates through the specimen is given by,

          Q_Tt = N_Aσ_T(ρt)/A ---------------------------------------- [2673a]
where,
          N_A -- Avogadro's number,
          σ_T -- The total scattering cross sectoin (including both elastic and inelastic scatterings, i.e. σ_elastic + σ_inelastic) for an isolated atom,
          ρ -- Atomic density,
          A -- The atomic weight of the atoms in the specimen which have a density of ρ and mass-thickness of ρt.

Furthermore, based on Rutherford theory and Equation 2673a, the total probability of scattering an electron is given by,

          ----------- [2673b]