Fluence

The fluence is a physical quantity to describe radiation or moving matter. For example, it describes the number of particles that have passed through a surface : ${\displaystyle \Phi }$ ${\displaystyle N}$ ${\displaystyle A}$

${\displaystyle \Phi ={\frac {N}{A}}}$

Their dimension is therefore number / area, their SI unit m ⁻² .

The fluence is the integral of a flux density over time: ${\displaystyle F}$

${\displaystyle \Phi =\int Fdt}$,

if the flux density remains constant over time, simply the product of flux density times time.

The fluence decreases with the distance  r from a point radiation source proportionally to 1 / r ² :

${\displaystyle \Phi \propto {\frac {1}{r^{2}}}}$

It decreases even more with increasing distance, if the material is absorbed or disintegrates on the way between the source and the observed surface .

Neutron fluence

Although the physical quantity neutron flux is not a vector field, in reactor physics the time integral over this quantity is also referred to as fluence in this case. Application example: According to the Federal Office for Radiation Protection, Castor containers of type V / 19 do not yet result in material embrittlement below a neutron fluence of 10 ¹⁸ neutrons / cm ² .

See also

• Particle flux density
• Neutron flux

Individual evidence

1. ↑ 2.2.1.2 Transport and storage casks of the type CASTOR® V / 19. (pdf; 1.1 MB) (No longer available online.) In: Approval for the storage of nuclear fuels in the on-site interim storage facility in the Bramsche district of the city of Lingen owned by Kernkraftwerke Lippe-Ems GmbH. Federal Office for Radiation Protection , November 6, 2002, pp. 60–61 , archived from the original on July 13, 2016 ; accessed on July 13, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.