Absolute soft X-ray measurements using an ion chamber

Measurements of soft X-ray absolute intensities have been carried out using a double ion chamber and monochromated synchrotron radiation. The chamber is cylindrical and 1.3 m long. The soft X-ray beam enters the chamber at a position off the central axis, and the produced ions are collected with electrodes on the opposite side to the photon entrance. An index constant for rare gas, the γ-value, which is the average number of electrons emitted from an atom having absorbed a photon, was used for obtaining the absolute photon intensity. The obtained intensity ranges from 1 Gphotons s⁻¹ to 25 Gphotons s⁻¹ in the energy range 72–800 eV. The estimated uncertainty is about 5–20% depending on the intensity and the spectral purity of the soft X-rays.