# Particle Fluence Units

Particle Fluence 20KeV.pdf (15.2 KB)

Hello,
I’m wondering if someone could point me in the right direction for the Fluence units I obtained from the tutorial. .

By definition, fluence phi (i.e. tracklength L density, cm/cm3) is expressed in 1/cm2 (or equivalent units).
Now, USRTRACK is meant to provide a differential fluence spectrum (as a function of particle energy) averaged over a region. If the actual region volume is specified in the scoring card, one gets dphi/dE in 1/(GeV cm2); otherwise, one gets dL/dE in cm/GeV, i.e. a differential tracklength spectrum, which can always be renormalized by the region volume when plotting.
If scoring with a logarithmic energy binning, aiming to plot the resulting spectrum as a function of log(E), one should then plot dphi/dlog(E) = E dphi/dE (where phi stands actually for L in case the region volume is not input), whose units become 1/cm2 (or cm).
Looking at the tutorial and your plot, your case appears to be the latter: you plotted dL/dlog(E) in cm (assuming an unitary volume in the USRTRACK card), whose integral in log(E) gives again cm and, after dividing by the region volume, the average fluence over the region in 1/cm2. Note that the (phi or L) integral is already calculated for you in the respective sum.lis file (where the cumulative spectrum, integrating from E to Emax, is also given).
All that has to be intended per beam particle.

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