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that the exposure is very likely due to the γ only. This
situation will create different contrast on the film, each
contrast owns different optical density.
Figure 6.5: Filmbadge
The measurement of optical density (OD) for each
film is done using densitometer by log of the transmis-
sion as describe by Equation 6.5. Where Io is an inten-
sity of light incident with the film and Ii is an intensity
of light pass through the film.
OD = log( Io ) (6.5)
Ii
However, contribution from possible radiation into
the background has to be considered. In this case,
the film used as a control should has the funtion to
record background radiation. Therefore, the value of
OD should be substracted from the transmission due
to the intensity of light from background, Ibg to give a
net optical density as describe in Equation 6.6.
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