The instrumentation used to measure the total absolute photoabsorption cross sections

Summary of ResultsThe results of our measurements supply theorists with the means to assess the predictivecapabilities of their theoretical models. They provide an impetus for the development of new theoretical methodologies. They imply that the scarcity of prior 1 to 10 keV measure-ments has seriously affected the accuracy of widely used soft x -ray cross section tables. They suggest that several theoretical models provide predictive capabilities at the 5% level, except near threshold energies. X -ray optics requires knowledge of soft x -rayphotoabsorption cross sections for a variety of neutral, ionized and excited states of anumber of elements. It is not feasible to perform laboratory measurements of all the photoabsorption cross sections of all the important states and stages of ionization. It is crucial to employ a theoretical model with known predictive capability. This study has shown that at 1 to 10 keV, several theoretical models have a 5% or better predictive capa-bility at most energies. Thus, theory is able to mend the crack in the foundation of x -ray