Cross section (physics)

In scattering, a differential cross section is defined by the probability to observe a scattered particle in a given quantum state per solid angle unit (i.e. within a given cone of observation) if the target is irradiated by a flux of one particle per surface unit:

Related Topics:
Scattering - Probability - Scattered particle - Quantum state - Solid angle - Cone - Flux

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:{d sigma over d Omega}={hbox{Scattered flux / Unit of solid angle} over hbox{Incident flux / Unit of surface}}

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The integral cross section is the integral of the differential cross section on the whole sphere of observation (4pi steradian):

Related Topics:
Integral - Steradian

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:sigma=int dOmega {d sigma over d Omega}

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A cross section is therefore a measure of the effective surface seen by the inpinging particles. Its unit is the surface unit.

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The cross section of two particles (i.e. observed when the two particles are colliding with each other) is therefore a measure of the interaction event between the two particles.

Related Topics:
Particle - Colliding

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