Fluence

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In physics, fluence or integrated flux 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.

It has two 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

\Phi = \frac{{\rm d} N}{{\rm d} a}.

2. Using the same image of a small sphere as above,

\Phi = \frac{\sum {\rm d \ell} }{{\rm d} V},

where dV is the infintesimal volume and \sum {\rm d \ell} is the sum of all the path lengths of the particles that transverse the volume.


[edit] References

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