LAUSR

Purpose Absolute measurement of radiant power in the X-ray region is essential for many applications in astrophysics, spectroscopy, and X-ray diagnostics. This paper presents a dependable method of absolute measurement of radiant power for synchrotron radiation monochromatized X-rays. Methods A free-air ionization chamber was examined closely and employed as the detector in the present work. Its measuring principle was discussed, and the correction factors were determined. Absolute measurement of radiant power for synchrotron radiation monochromatized X-rays in the region of 6–20 keV was performed using the free-air ionization chamber at Beijing Synchrotron Radiation Facility. As a verification and an important application, photodiodes were calibrated against the free-air ionization chamber. Results Relative standard uncertainties of absolute measurement using free-air ionization chamber are about 1%. Calibration of photodiodes within the photon energy range from 6 to 20 keV has relative standard uncertainties below 1.5%. Conclusion The free-air ionization chamber is qualified to be used in many disciplines to support the measurement of optical radiation.