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It is different from Rutherford scattering that has m_{α} (α particle) << M (gold nucleus), the situation here is that a heavy charged particle M interacts with an orbital electron me (M >> m_{e}). Figure 4418 shows the Coulomb interaction between the heavy charged particle (charge ze and mass M) and the orbital electron (charge e and mass m_{e}).
Figure 4418. Schematic diagram of a collision between a heavy charged particle M and an orbital electron m_{e}.
Using the conservation of angular momentum, we can know the momentum transfer Δp can be given by,
 [4418a]
In the case of a heavy charged particle (ze) interacting with a stationary
orbital electron (e) the scattering angle θ ≈ 0 and thus, Δp can be simplified by,
 [4418b]
The energy transferred to the orbital electron from the heavy charged particle for a single interaction with an impact parameter b is given by,
 [4418c]
