Characteristic curves for six different emulsions have been obtained with nuclear radiations of a wide range of specific ionization. Sources included α-particles, protons, neutrons, and &b.beta;-, γ- and X-rays. The two most sensitive films (Eastman Type K and Dupont Type 555) exhibited characteristic curves identical in shape for all exposures. Curves for the remaining films were found to be dependent on the type of radiation. When log density was plotted against log exposure, the curves fell into two groups. For particles with specific ionization equal to or greater than that produced by 30 keV X-rays, the slope in the linear region approached 1.0. For high-energy &b.beta;-rays, γ-rays and electrons, slopes greater than 1.0 were obtained. In most cases identical saturation densities were observed. Data are presented which show that γ-ray characteristic curves can be simulated with &b.beta;-rays. This technique can considerably simplify exposure procedures, particularly where high-level exposures are involved.