Absolute measurement of the photoionization cross section of atomic hydrogen with a shock tube for the extreme ultraviolet

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Abstract
The photoionization cross section of HI was measured at 19 wavelength points from 910 to 609 Å with experimental uncertainties between 7 and 20%. An aerodynamic shock tube, equipped with explosively driven shutters, was used to produce fully dissociated hydrogen and neon gas mixtures for the photoabsorption measurements. A description of the new shock-tube facility and a discussion of the experimental techniques are presented. Since our results agree with well-established theory, the reliability of our apparatus and methods for making measurements of this kind has been demonstrated. The measurement is the first in a continuing program to measure the photoionization cross sections of HI, OI, CI, and NI.