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Quantum Efficiency in Photographic X-ray Exposures

D. Bromley, R. Herz

Proceedings of the Physical Society Section B, 1950

14 citations

Abstract

The grain yield per absorbed quantum has been evaluated experimentally for four different photographic emulsions over a wavelength range of 1·-0.01 A., i e. from very soft X rays to gamma rays emitted from radium The tests were carried out with both heterogeneous and monochromatic X rays A grain yield of 1.0 per absorbed quantum appears to hold within a range of wavelengths of 1.2-0 37 A. (10 kV -33 kV). From 0.37 A. to short wavelengths (gamma rays) an increase of grain yield linear with quantum energy is obtained At a wavelength of 0.0123 A (1,000 kV.) about 80 grains are rendered developable per quantum absorbed The rate of increase of grain yield with quantum energy is different for different emulsions. For a slow and fine-grain chloro-bromide emulsion the grain yield was found to be less than unity for wavelengths below 0.12 A (i.e 100 kV) The results are consistent with the hypothesis that grains are made developable not only by the direct action of X rays but also by secondary electrons produced by the X rays. These are effective only when they are energetic enough to reach grains in the neighbourhood of that absorbing the original X-ray quantum.

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