Multi-concentric-ring open-air ionization chamber for high-intensity X-ray beams

An ionization chamber with four concentric ring electrodes was used to measure doses of white, 10, 15 and 20keV synchrotron X-ray beams. The ring-shaped electrodes, which had diameters less than 11.8mm, collected charges independently only around the beam, excluding strong in-beam charges when the beams passed through a small hole in the electrode centers. As a result, under low saturation voltages, the measured dose rates were confirmed to correlate with the beam intensity when conversion factors calculated with a Monte Carlo code were employed. The influence of the assumed beam sizes and incident positions on the current was almost negligible, with the exception of the incident position dependence at 10keV.