Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

Latent Image Formation
Latent image formation is a very subtle change in the silver halide grain of film.
The process may involve the absorption of only one or, at most, a few
photons of radiation and this may affect only a few atoms out of some 10 9 or
10 10 atoms in a typical photographic grain. Formation of the latent image,
therefore, cannot be detected by direct physical or analytical chemical means.
The process that made an exposed photographic grain capable of
transformation into metallic silver (by the mild reducing action of a developer)
involved a concentration of silver atoms at one or more discrete sites on the
photographic grain. In industrial radiography, the image forming effects of X-
rays and gamma rays, rather than those of light, are of primary interest.
The agent that actually exposes a film grain (a silver bromide crystal in the
emulsion) is not the X-ray photon itself but rather the electrons (photoelectric
and compton) resulting from an absorption event.
The most striking difference between X-ray and visible light exposures arises
from the difference in the amounts of energy involved.
Charlie Chong/ Fion Zhang