Fluence

The quotient of $dN$ by $da$, where $dN$ is the number of particles incident on a sphere of cross-sectional area $da$, thus:

$\Phi = \frac{dN}{da}$

The unit of fluence is m-2.

(Adapted from ICRP Publication 116, 2010)

The quotient of $dN$ by $da$, where $dN$ is the number of particles incident on a small sphere of cross-sectional area $da$, thus:
$\Phi = \frac{dN}{da}$