Autoradiography can be used to study the local distribution of the radioactive iso­topes. The distribution of the isotopes in the different objects and organs is studied by stripping films or X-ray films. Similar to the photo emulsions used in black- and-white photography, they contain silver bromide particles in a gelatin emulsion. When irradiating, Ag(I) ions are reduced to metallic silver. This reduction takes place only in those spots where the radiation touched AgBr. The silver particles are then magnified by a chemical procedure called “development.” The formation of metallic silver causes the blackening of the film, and a negative image is obtained. The intensity of the blackening is proportional to the intensity of radiation. Similar to traditional photography, a positive image can be produced from the negative image. On the positive image, the places exposed to high radioactive intensity become white.

As mentioned previously in this section, stripping films are frequently applied to autoradiography. These films may be in close contact with the sample, improving the quality of the autoradiographs.

In Figure 8.3, a negative autoradiogram of the radiocolloid formation is illus­trated. Moreover, in Figure 14.9, an autoradiogram (left) and a microscopic picture (right) of etched tin alloy containing 10_7% 111Ag are shown. As seen, the intro­duction of the radioactive silver takes place on the boundaries of the particle in the polycrystal.

An application of autoradiography in medical science is shown in Figure 14.10.