

Establishing a "transport formula"
Due to particle conservation, the number of particles within a
small volume element
∆
V can be obtained from 4 processes:
j
d
N
=
j,in-out
d
N
−
j,att
d
N
−
j,secondaries
d
N
+
j,source
d
N
+
Note: The index j refers to a particular type of particle
j,in-out
d
N
j,att
d
N
−
j,secondaries
d
N
+
j,source
d
N
+
the net number of particles j flowing in and out of the
volume
∆
V
the number of particles j that are attenuated in
∆
V
the number of particles j that are born by
interactions with medium atoms in
∆
V
the number of particles j produced by the sources
inside the volume
∆
V
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