Characteristics of three nuclear emulsions for autoradiography at the electron microscope.

Abstract

On account of their low grain size three commercial emulsions, Gevaert NUC 307, Ilford L4 and Kodak NTE have been investigated to assess their qualities for electron microscope microautoradiography. Grain size distribution curves were determined and a developer suitable for microautoradiography was selected after having tested different types of developers. In order to investigate the sensitivities of the three emulsions, monolayer preparations were irradiated in the electron microscope, using an energy of 5.7 keV corresponding to the mean β-energy of tritium. After exposure the specimens were developed but left unfixed. The sensitivity may then be determined using the percentage of developed grains. For the formation of one latent image the Ilford L4 emulsion must be hit on the average by 1 – 1.4 electrons per AgBr grain; the corresponding figures for Gevaert NUC 307 and Kodak NTE are 2 – 3 and 4 – 5 respectively. The problem of resolution of point and plane sources of radioactivity is discussed. Future advances in microautoradiography will depend on the development of emulsions with lower grain sizes, but such improvement must not be at the expense of sensitivity.