Absolute measurement of photon flux using ionization chamber in (6~20) keV synchrotron radiation X-rays

Absolute measurement of photon flux under high-fluence rate X-rays was required in photon diagnostics for X-ray lasers. A free-air ionization chamber used for the reproducibility of air-kerma in high-fluence rate X-ray was designed, and the monoenergetic X-rays flux of (6–20) keV were absolutely measured on Beijing Synchrotron Radiation Facility. The energy spectrum of the monoenergetic X-rays was measured using a silicon drift detector, and the proportion of higher harmonics was determined. The saturation curve, air attenuation correction factor, and composite loss correction factor of the free-air ionization chamber were obtained experimentally. The air-kerma rate for the (6~20) keV monoenergetic X-ray was measured accurately, and the relative combined standard uncertainty of the air-kerma is 0.61%.