11.2: Some terminology for general scattering
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The incident flux (I) of particles with momentum p=ℏk is the number of incident particles crossing unit area perpendicular to the beam direction per unit time.
The scattered flux (S) of particles with momentum p′=ℏk′, is the number of scattered particles scattered into the element of solid angle dΩ about the direction θ, ϕ per unit time per unit solid angle.
The differential cross section is the ratio of the scattered flux in direction θ, ϕ to the incident flux.
dσdΩ=S/I
The total cross section is the ratio of the scattered flux in any direction to the incident flux.
σT=∫∫dσdΩsinθdθdϕ