Cross section converter
Convert nuclear and particle cross sections between barns and SI areas — how big a nucleus looks to a passing particle.
That's 100,000,000,000,000,000,000× as big as a neutrino interaction, while ordinary neutron scattering is 4× bigger. A disc that size would have a radius of about 5.642 fm.
What it means
How big a target is that?
A cross section is an effective area, not a physical one. A strongly absorbing nucleus can present a target far larger than itself.
Every unit
Your cross section in every unit
Learn
Three things worth knowing
-
1 barn = 10⁻²⁴ cm²
Or 100 square femtometers. It is one of the few units chosen to make the numbers come out near 1 for everyday nuclei.
-
As big as a barn door
Physicists on the Manhattan Project found uranium’s cross section surprisingly large and joked it was "as big as a barn". The name was kept, partly because it was meaningless to anyone listening in.
-
It is not the nucleus’s size
Xenon-135 has a cross section of 2.6 million barns, far bigger than the atom itself. Cross section measures how likely an interaction is, in units of area.
Shortcuts
Popular cross section conversions
Background
About the barn
A barn is 10⁻²⁸ m², about the area of a uranium nucleus. Neutron capture probabilities are quoted in barns, and particle physics in the much smaller picobarn and femtobarn.