A program to obtain reliable photoabsorption cross sections

A program to obtain reliable photoabsorption cross sections for a broad range of elements has been initiated at Lawrence Livermore National Laboratory. Using well-characterized samples, absolute measurements have been made with overall uncertainties of /+-/10% or less over energy ranges from about 50 eV to several keV, at several synchrotron radiation facilities. More than a dozen elements have been investigated and other measurements are being planned for elements beryllium (Z-4) through uranium (Z-92). Among the interesting phenomena observed are the resonances/enhancements which seem to accompany virtually every inner shell threshold. Specific examples discussed in this paper include carbon, nickel and uranium. Comparison with theory and existing data compilations/data bases indicate the need for substantial theoretical and compilation improvements. 24 refs., 6 figs