Understanding Neutron Radiography

The shoulders of the curves for industrial X-ray films, and of the directexposure
type of medical X-ray films, come at densities far above those that
can be viewed on available illuminators. Changes in the slope of the
characteristic curve have a definite relationship to the visibility of details in the
radiograph. For example, two slightly different thicknesses in the subject will
transmit slightly different exposure to the film. The exposures will have a
certain ration, i.e., will have a certain log exposure difference between them.
The difference in densities corresponding to the two exposures will depend
upon just where on the characteristic curve they fall; the steeper the curve,
the greater will be the density difference. This means that a certain log
exposure interval in the middle of the curve of Fig. 7.1 will correspond to a
greater density difference than the same interval at either end.
Charlie Chong/ Fion Zhang
Practical.NR Chapter 7