Varian Linatron High-Energy X-ray Applications 2007

FIGURE 4-2. Film response curves for three industrial X-ray films
with relative speeds (exposure factors, EF): 1 = Fast, 3 = Medium,
7 = Slow.
If an object with varying thicknesses (steps) is radiographed,
the densities of the steps on each film, when plotted, will
appear as shown in Figure 4-4. These points also show that
the density differences, and therefore the contrast, are larger
with slower film. This further illustrates the general rule
that contrast increases with increased film density.
A numerical value for contrast can be taken from this plot.
Example
For the 1/8th-inch steel steps, the slope of the curve is
approximately 0.20 density units per 1 /8-inch step at the
2.0 density point. This value corresponds to the contrast
achieved with lead intensifying screens. It shows the
increased contrast achieved with phosphor screens.
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FIGURE 4-3. Curves of gradient versus film density for three Xray
films shown in Figure 4-2.
FIGURE 4-4. Film density plot for step exposures of steel for lead
screens at 2 MeV. *
Varian Linatron applications