SOME THEORETICAL ASPECTS OF RADIOAUTOGRAPHY

Abstract

The purpose of radioautography (also called autoradiography or autography) is to identify the presence of radio-elements within microscopic structures by the action of the emitted radiations on photographic emulsions. Since the quality of the photographic image depends on its resolution and density, a theoretical study of these two characteristics was made. For resolution studies, a theory based on an inverse square law relationship for β-ray intensity is expanded to include various geometric shapes of radioactive sources encountered in microscopical preparations. The formulae provide a means to calculate the resultant distri bution of photographic blackening (density), from which it is possible to deter mine how the resolving power is influenced by the geometrical relations between the tissue preparation and photographic emulsion. For density studies, a theory is presented whereby it has been possible to arrive at the average number of impacts of given β-particles required to render a medium contrast emulsion grain developable. The basis of the theory rests on calculating the mean energy dissipated by a β-particle in traversing a silver bromide grain, and determining from this the number of reduced silver atoms deposited per grain. Realizing the average number of silver atoms necessary to render a grain developable, the required number of impacts by a β-particle may then be calculated. An example is given in which j8-particles of a mean energy equal to that given off by radioiodine are made to react with the so-called medium contrast emulsion.