Nuclear Cross Section
A measure of the probability that a particular nuclear reaction will occur between a nucleus and an incident particle.
Formula / equation
σ, measured in barns
Unit
barn
In depth
Expressed as an effective target area in barns, where one barn is 10⁻²⁸ m², the cross section can be far larger or smaller than the physical size of the nucleus. It depends strongly on the energy of the incident particle, peaking sharply at resonance energies.
Examples in the real world
Uranium-235 has a thermal fission cross section of 585 barns; boron-10 absorbs neutrons at 3840 barns.