Spectral Sensitivity of Two Commercial X‐Ray Films between 0.2 and 2.5 Angstroms Available to Purchase

The spectral sensitivities of Kodak No‐Screen and Kodak Industrial Type K X‐Ray Films were determined in the region between 0.2 and 2.5A using the filtered K fluorescence of several irradiated elements as approximately homogeneous radiation. Exposures in roentgens were obtained with an air ionization chamber designed especially for the purpose. Curves are given showing the number of roentgens incident on the film which will give a developed photographic density of 1.0 above fog for the various wave‐lengths. The K limits of silver and bromine are prominent. The maximum sensitivity in terms of roentgens occurs at about 0.4A, but the marked decrease found by other observers at shorter wave‐lengths is probably obscured by inaccuracies. From the energy value of the roentgen, the sensitivity of the films is expressed as the incident ergs per square centimeter required to produce a density of 1.0 above fog. Computations from these results show that as the wave‐length increases the films utilize the absorbed energy more efficiently. On the other hand, high energy quanta are more efficient than low energy quanta but not in proportion to their energy. In addition to the more or less gradual change with wave‐length of efficiency of utilization of absorbed energy, there is evidence for sudden jumps at the K limits of Ag and Br. Qualitative explanations are given for the observed changes in efficiency.