autoradiography

autoradiography [¦ȯd·ō‚rād·ē′äg·rə·fē]

(engineering)

A technique for detecting radioactivity in a specimen by producing an image on a photographic film or plate. Also known as radioautography.

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Autoradiography

A photographic technique used to localize a radioactive substance within a solid specimen; also known as radioautography.

A photographic emulsion is placed in contact with the object to be tested and is left for several hours, days, or weeks, depending on the suspected concentration of the radioactive material to be measured. The emulsion, which is a gel containing silver halide, is then developed, fixed, and washed as in the usual photographic process. At sites where the emulsion was close enough to the radioactive substance, it appears dark because of the presence of silver grains. When the number of grains is insufficient to darken the film to the unaided eye, the film may be examined with the aid of a microscope. The individual silver grains may then be seen. The pattern formed by the grains depends on the type of radiation and the nature of the photographic emulsion. Alpha particles produce short, straight rows or tracks of grains. Beta particles as well as x-rays and gamma rays, which affect film by producing beta particles, produce tortuous tracks whose lengths and grain densities depend on the energy of the beta particles. Low-energy particles produce shorter tracks with higher grain densities. Very low energy particles like those from tritium (3-hydrogen) may produce only a single grain very close to the site of decay.

Autoradiography can be used to detect, and measure semiquantitatively, the radioactive materials in almost any object that can be placed in contact with film or photographic emulsion in some form. However, in biological research the object may be (1) a whole plant or animal that can be flattened against a film; (2) the cut surface of a plant or animal, or one of its organs; (3) thin sections of tissues or cells; (4) squashed or otherwise flattened cells; (5) surface films produced by spreading on water the protein monolayers containing DNA or ribonucleic acid (RNA) that are picked up on grids for electron microscopy; (6) sheets of paper or other materials on which radioactive substances have been separated by chromatography or electrophoresis; or (7) acrylamide gels in which DNA, RNA, or proteins have been separated by electrophoresis.