A method has been developed for finding the half-intensity width, to an accuracy of ±5%, of the profiles of spectral lines photographed in the vacuum ultraviolet. Plate calibration is achieved by an aperture restriction device placed at the Sirks focus of a 3-meter normal incidence vacuum spectrograph. This gives a stepped intensity in the focal plane with a standard ratio of 2:1. The measurement is not affected by reciprocity law failure or intermittency effect in the photographic emulsion, and can be used with pulsed light sources.
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