The quantity kind $\textit{Particle Fluence}$ is the total number of particles that
intersect a unit area in a specific time interval of interest, and has units of $m^{-2}$
(number of particles per meter squared).
Applicable units are those of quantitykind:ParticleFluence
http://en.wikipedia.org/wiki/Fluence
https://cdd.iec.ch/cdd/iec61987/iec61987.nsf/ListsOfUnitsAllVersions/0112-2---62720%23UAD133
"Particle Fluence" is the total number of particles that intersect a unit area in a specific time interval of interest, and has units of /m2 (number of particles per meter squared).
$\Phi = \frac{dN}{dA}$, where $dN$ describes the number of particles incident on a small spherical domain at a given point in space, and $dA$ describes the cross-sectional area of that domain.
http://www.iso.org/iso/catalogue_detail?csnumber=31895