From absorption and photoionization spectra of Ar, Kr, and Xe obtained at 0.5-Å bandwidth, absorption cross sections were computed, and the absolute flux distribution of the Hopfield helium continuum was determined between 600 and 1000 Å. Both total absorption and partial absorption methods were used in deriving flux distributions. Ionization was measured in a parallel-plate ion chamber. In addition, the oscillator strengths for the metastable or autoionized levels lying in the ionization continua were determined.
P. H. METZGER and G. R. COOK, "Flux Distribution of the Hopfield Helium Continuum from the Photoionization of Ar, Kr, and Xe," J. Opt. Soc. Am. 55, 516-520 (1965)