Reciprocity Failure and Latent-image Fading in Autoradiography

Abstract

The dependence of the density given by emulsions exposed to 131I on the intensity and exposure time has been examined for times in the range of minutes up to days, such as are normally used for autoradiography exposures. The tests were made by exposing emulsions for series of times in contact with three sources all containing the same silver iodide content, but whose specific activities had a range of accurately predetermined values. The results all appeared to obey the reciprocity law, except with exposure times of such a duration that appreciable latent-image fading occurred during the exposure. Latent-image fading can, however, be eliminated by storing the coated plates in dry nitrogen or carbon dioxide. These methods should prove particularly valuable when exposures are made to isotopes of half-life longer than 30 days, and for improving the quantitative reproducibility of autoradiographic exposures.