Detector calibration in the wavelength region 10 nm to 100 nm based on a windowless rare gas ionization chamber

A detector calibration facility based on a rare gas ionization chamber has been built at the Electrotechnical Laboratory, Japan. We have realized a windowless system by applying strong differential pumping, which features no spectral limitation and easy gas handling. In the auto-ionization region near the xenon absorption edge, photon flux was found to be underestimated and this limited the maximum available wavelength to 92 nm. The uncertainty (1 sigma) for a Si photodiode calibration was estimated to be within +/-9% in the wavelength range 10 nm to 92 nm.