The absolute photoabsorption cross section of atomic sodium in the region above the 2p threshold (45-250 eV)

The photoabsorption cross section of sodium has been determined in the energy range 45-250 eV using a heat-pipe absorption cell and a synchrotron light source. The results are compared with previous relative values and with a single-electron calculation. The integrated oscillator strength for the n=2 shell is compared with that of neon. The problems of determining accurate cross sections for metal vapours in the extreme ultraviolet spectral region are discussed in some detail.