Fluence

The fluence is a physical quantity for the description of particle radiation. It is the number of particles that pass through an area:

Their dimension is therefore number / area, its SI unit m -2.

The fluence is the integral of the flux density over time:

It decreases with the distance r from a point source of radiation in proportion to 1/r2:

The fluence decreases even more with increasing distance, if the particles are absorbed in the path between source and considered surface or disintegrate.

Example: Castor casks of the V/19 is not to be expected according to the Federal Office for Radiation Protection below a neutron fluence of 1018 Neutronen/cm2 with material embrittlement.