Equation 10 has not been normalized to one unit over all space. It is the integration over the radial coordination of the 3D PDF that has been normalized to one unit at the origin. 4𝜋𝑟 2 (𝑑𝑟) is the shell volume that has the same distance to the origin and 𝑒 -𝑟 2 4𝐷 𝑟 ∆𝑡 is the probability density of finding the particle in this shell volume [r, r+dr] at ellipse time Δt.