X-rays affect a photographic emulsion in the same way that light does. Absorption of X radiation by any substance depends upon its density and atomic weight. When the human body is X-rayed, the bones, which are composed of elements of higher atomic weight than the surrounding flesh, absorb the radiation more effectively and therefore cast darker shadows on a photographic plate. Radiation consisting of neutrons is now used in some types of radiography and produces almost opposite results.
