“…In the last decade the use of vuv radiation has steadily been growing. Today radiometric techniques are well established with calibrated transfer standard sources for wavelength 3115 nm, such as the deuterium lamp (Einfeld et a1 1978, Key andPreston 1980), and the wall-stabilised argon mini-arc (Bridges and Ott 1977, Einfeld er a1 1979). In the wavelength region below 115 nm, reliable and easy to use transfer standard sources are still missing.…”