Assessment of resolution by half distance values for tritium and radioiodine in electron microscopic radioautographs using Ilford L4 emulsion developed by “Solution Physical” or D-19b methods

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Abstract
Half distance values for electron microscopic (EM) radioautographs with the isotopes3H and125I were determined using Ilford L4 emulsion processed with either fine grain, solution physical development, or filamentous grain, chemical development with D-19b.3H- and125I-line sources, obtained by cutting perpendicular sections from sections of3H-labeled methacrylate or125I-labeled thyroid glands, were processed for EM radioautography. The distribution of silver grains around a line source was determined by measuring their distance from the source in photographs of EM radioautographs. The number of silver grains per unit distance from the line source was plotted on graphs and half distance values were calculated. With solution physical development, the half distance value was 76 nm for3H and 80 nm for125I; whereas with D-19 b development it was 187 nm for3H and 157 nm for125I. Since solution physical development produced a reduction of about 50% in the half distance values for both isotopes, it is concluded that the production of fine grain by this method provides better resolution for EM radioautography than filamentous grain development with D-19 b.