Absolute fluence rates of soft X-rays using a double ion chamber

Absolute fluence rates of soft X-rays have been measured using a multi-electrode ion chamber. The measured ion currents approached a constant value when the gas pressure became lower than about 0.1 Pa, showing that secondary ionization does not occur in the chamber under the low-pressure. A fitting calculation with consideration of secondary ionization by ejected electrons has reproduced plotting curves of experimental ion currents against gas density in the region of 10(-2) to 10(3) Pa. The fluence rates were obtained from 50 to 1100 eV: e.g. the absolute fluence rate at the photon energy of 900 eV was 4.2x10(9) photons/s with an Al filter under the storage ring condition of 750 MeV and 100 mA. (C) 1999 Elsevier Science B.V. All rights reserved.