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| {{about|the concept of fluence in physics|the car|Renault Fluence}}
| | Her title is Felicidad Ahmad. Climbing is what love doing. Years in the past we moved to Arizona but my spouse wants us to move. Interviewing is how I make a living and it's something I truly appreciate.<br><br>My page; [http://Mcb-law.net/great-ideas-about-auto-repair-that-you-can-use/ mcb-law.net] |
| {{Expert-subject|Physics|date=February 2009}}
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| 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<sup>–2</sup> (number of particles per meter squared). Fluence can also be used to describe the energy delivered per unit area, in which case it has units of J/m<sup>2</sup>. It is considered one of the fundamental units in [[dosimetry]].
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| In light based medicine and dentistry, fluence, which may be more properly referred to as [[radiant exposure]], is a measurement of energy over area. The area is usually the spot size of the light device.
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| It has two equivalent definitions:
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| 1. Suppose ''N'' particles pass through an area ''A''. The particle fluence for the area A is defined as:
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| ::<math>\Phi = \frac{N}{A}</math>.
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| In the limit of infinitesimal area, this is:
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| ::<math>\Phi = \frac{{\rm d} N}{{\rm d} A}</math>.
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| 2. Imagine an infinitesimal volume d''V'' with particles passing through it. The particle fluence can be defined as
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| ::<math>\Phi = \frac{\sum {\rm d \ell} }{{\rm d} V}</math>,
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| where <math>\sum {\rm d \ell}</math> is the sum of all the path lengths of the particles that traverse the volume. These definitions are equivalent as can be seen by multiplying the first definition by <math>{\rm d} x/{\rm d} x</math> where d''x'' is the typical path length of a particle in the volume. The numerator (<math>{\rm d}N {\rm d} x</math>) then gives the total path length traced out by the d''N'' particles in the volume (<math>{\rm d}N {\rm d}x \simeq \sum {\rm d \ell}</math>) while the denominator (<math>{\rm d} A {\rm d} x</math>) gives the volume d''V''.
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| ==References==
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| {{reflist}}
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| * [[International Commission on Radiation Units and Measurements|ICRU]] 33: Radiation Quantities and Units, April, 1980. (www.icru.org)
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| {{SI_radiometry_units}}
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| [[Category:Nuclear physics]]
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| {{nuclear-stub}}
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Her title is Felicidad Ahmad. Climbing is what love doing. Years in the past we moved to Arizona but my spouse wants us to move. Interviewing is how I make a living and it's something I truly appreciate.
My page; mcb-law.net