Fluence Explained: What is it & How Does it Work?

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Fluence is defined as the total number of particles passing through a unit area over a specific time interval, measured in particles per square meter. The discussion raises a question about how fluence can be greater than zero without a defined timing interval, which is typically associated with flux. It is suggested that fluence represents a snapshot in time, but this perspective leads to confusion, as an infinitely small time interval would imply fluence approaches zero. The distinction between fluence and flux is emphasized, with fluence being the integral of flux over time. Understanding the relationship between these concepts is crucial for clarity in physics discussions.
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I am new to the fluence concept which is apparently the number of particle passing through an area.

However how can this quantity ever be greater than zero...? In my mind there needs to be a timing interval to compute how many particles are passing through the area which I know is referred to as the flux.

My professor explains this concept as a snapshot in time but that to me is flux. As the snapshot in time becomes infinitely small this 'fluence' should go to zero... right?

Any thoughts?
 
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Per wiki:

In physics, fluence is the flux (either particle or radiative flux) integrated over time. For particles, it is defined as 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).
 

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