Autoradiography

Abstract

This chapter focuses on autoradiography, which is a technique for detecting radioactivity through the formation of silver grains in a photographic emulsion. An emulsion consists of crystals of silver halide, usually silver bromide, suspended in gelatin. To increase their sensitivity, nuclear emulsions designed for autoradiography have a higher ratio of silver halide to gelatin. Autoradiography is based on the same principle as photography except that the energy for conversion of silver bromide to metallic silver is derived from ionizing radiation rather than from photons of light. Silver bromide crystals contain sensitivity specks, which are irregularities in the crystal lattices. The free electrons migrate to sensitivity specks and attract silver ions, which combine with the electrons to form atoms of silver. A latent image of the autoradiogram is formed when enough silver atoms accumulate at a sensitivity speck to form a nucleus of metallic silver that catalyzes the conversion of the entire crystal into a silver grain during development. Unreduced crystals are preferentially dissolved in the fixer, leaving behind a pattern of silver grains that denotes the presence of radioactive material. © 1979, Elsevier Inc. All right reserved.