Understanding Neutron Radiography Reading V-Kodak Part 2 of 3

A simple means for applying this method to routine work is as follows:
Parallel lines are drawn on a transparent plastic sheet, such as a fixed-out x-
ray film, in the manner shown in the figure below. The spacing between the
base line and the line immediately above is the log relative exposure interval
for Film X between D = 1.0 and D = 3.5. It is laid off to the same scale as the
ordinate (vertical) scale of the exposure chart. Similarly, the distance from the
baseline to any other line parallel to it can be made to correspond to the log
relative exposure interval for other density limits and films. This transparent
guide is moved up and down on the exposure chart with its lines parallel to
the thickness axis. The two guidelines being used form a rectangle with the
two vertical lines of the exposure chart that mark the thickness limits of the
specimen. The correct kilovoltage is the one whose graph intersects
diagonally opposite comers of the rectangle. If the film type used is the one
for which the chart was prepared, the correct exposure is indicated at the
intersection of the upper guide line with the exposure scale (Point C Figure 1).
If a different film is used, a suitable correction factor obtained either from
tables of relative speeds or by the method described in Example 2 in "Overlay
Methods" and "Nomogram Methods", must be applied to the exposure as
determined from the chart.
Charlie Chong/ Fion Zhang
Radiography in Modern Industry. Rochester, NY: Eastman Kodak Co. 1980