Fluence

In physics, fluence is defined as the number of particles that intersect a unit area . Its units are m^-2 (Number of particles per meter squared). In particular, it is used to describe the strength of a radiation field, in which case the unit used is J/m². It is considered one of the fundamental units in dosimetry.

Additional recommended knowledge

Recognize and detect the effects of electrostatic charges on your balance

How to quickly check pipettes?

Daily Sensitivity Test

It has two equivalent definitions:

1) Imagine that an infinitesimal sphere of cross sectional area da is impinged upon by dN particles of a certain type. Then, the fluence is:

.

2) Using the same image of a small sphere as above:

,

where dV is the infintesimal volume and is the sum of all the path lengths of the particles that transverse the volume.

References

ICRU 33: Radiation Quantities and Units, April, 1980. (www.icru.org)