X-ray film response in the 9–70-keV range was measured for exposures as short as 3 nsec corresponding to dose rates as high as 10<sup>17</sup> photons/cm<sup>2</sup>/sec. Thermoluminescent dosimeters were used as calibration standards to normalize the film results. The ratio of film response at high dose rate divided by film response at low dose rate was used as a measure of reciprocity failure. No definitive reciprocity failure could be observed within the experimental error of 10%–15%, but there appears to be a slight trend towards reciprocity failure at lower energies.
L. S. BIRKS, R. R. WHITLOCK, J. S. VIERLING, D. J. NAGEL, and S. G. GORBICS, "Reciprocity of X-Ray Film Response for Nanosecond Exposures," J. Opt. Soc. Am. 60, 649-653 (1970)