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

Development
Many materials discolor with exposure to light (some kinds of wood and
human skin are examples) and could be used to record images. Most of these
materials react to light exposure on a 1:1 basis — one photon of light alters
one molecule or atom. In the silver halide system of radiography, however, a
few atoms of photolytically deposited silver can, by development, be made to
trigger the subsequent chemical deposition of some 10 9 or 10 10 additional
silver atoms, resulting in an amplification factor on the order of 10 9 or greater.
This amplification process can be uniform and reproducible enough for
quantitative radiation measurements. Development is essentially a chemical
reduction in which silver halide is converted to metallic silver. To retain the
photographic image, however, the reaction must be limited largely to those
grains that contain a latent image; that is, to those grains that have received
more than a prescribed minimum radiation exposure.
Charlie Chong/ Fion Zhang