Electron-atom source as a primary radiometric standard for the EUV spectral region

A compact, portable radiometric standard for the EUV wavelength region utilizing single photon counting is described. An energetic beam of electrons is passed through a thin atomic or molecular gas target inducing radiative transitions. The absolute flux of radiation per unit length of beam emitted in a spectral line can be calculated from the current of electrons and the number density of the target gas if the relevant electronimpact photoemission cross section is known at the electron-impact energy used. In typical operating conditions and for a photoemission cross section of 10(-22) m(2), the emitted flux of photons can be 10(10) photons/s/cm of beam length resulting in a count rate of 500 counts/s into an f/6 spectrometer-detector system. Assessment of previously measured electron-impact photoemission cross sections indicates that, once precision benchmark cross-sectional measurements are available, ultimate uncertainties as low as 3% could be obtained for this standard.