Varian Linatron High-Energy X-ray Applications 2007

The total unsharpness is reduced to include only inherent
and geometrical unsharpness because they contribute much
more than spot size to unsharpness. This reduces the
expression the expression above to the following.
UTOT = (U 2
F + UG2 ) 1/2
Example
Let energy equal 2 MeV and focal spot equal 2 mm. If we
use double emulsion film and automatic development,
with U F = 0.3 mm, and a radiography arrangement where
6 inches of steel are exposed with a D/T = 12, U TOT is:
U TOT = (0.3 2 + (2/12) 2 ) 1/2 = 0.34 mm
From this example, it can be seen that with a film
unsharpness of 0.3, the geometric value only has a slight
effect on the total. Figure 4-7 shows total unsharpness
plotted for the case where inherent unsharpness is 1 mm.
The plots show the effect of various values of D/T on the
total unsharpness.
FIGURE 4-7. Total unsharpness as a function of source spotsize.
page 24
Sensitivity and Image Quality
A standard requirement in most high-energy radiography
applications with Linatron sources is that the inspection
process demonstrates 2% sensitivity using penetrameter
wires or holes. Linatron radiography regularly produces
sensitivities better than 1% through a wide range of
material thicknesses. Many factors determine image
quality in all high-energy Linatron radiography
applications. Thickness, wire penetrameter, plaque
penetrameter, and radiographic sensitivity are four kinds of
sensitivity commonly evaluated determine Linatron
capability.
Thickness Sensitivity. Thickness sensitivity refers to the
ability of the radiographic inspection to demonstrate a
thickness step by seeing the density difference produced on
the film. Under good viewing conditions a trained eye can
reliably perceive 0.006 density units with a reasonably
sharp step edge in the image. This minimum perceptible
density difference varies with energy and object thickness
depending on the energy of the source and the contrast
achieved by the film and screens. All Linatron sources can
provide approximately 1% thickness sensitivity from 1 inch
(25.4 mm) of steel up to 10 HVL thicknesses using finegrained
film, lead screens and good scatter control.
Wire Penetrameter Sensitivity. Wire penetrameters are
generally used in Europe, and in several special applications
in the United States. The German D.I.N. wires come in
16 sizes from 3.2 mm to 0.10 mm as follows: 3.2, 2.64,
2.0, 1.6, 1.32, 1.0, 0.8, 0.66, 0.5, 0.4, 0.33, 0.25, 0.20,
0.165, 0.15, and 0.10 mm.
Data shows that all Linatron sources should demonstrate
better than 1% sensitivity above 1 inch (24.5 mm) of steel,
and should achieve better than 0.5% for steel thicknesses at
about 6 inches (152.4 mm).
Varian Linatron applications