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We follow a proof given by A. B. Chilton in 1977 (Health Physics 34, 1978)
Ω
Consider the small irregular
volume of interest
∆
V.
Assume a radiation field with
5.2
Appendix: Alternative definition of fluence
∆
V
particles of any
arbitrary
directional distribution
.
However,
initially
consider
only those particles going
in the direction
Ω
.
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