Normalized air-kerma calibration coefficients, N K, measured with ionization chambers biased to (a) −300 V (positive charge collection) and (b) +300 V (negative charge collection) for x-ray beams with effective energies ranging from 11.5 to 145 keV. The material specification next to each chamber model in the legend denotes the collecting electrode material. The uncertainty at the k = 2 level for the N K measurements was 1.5%.
Normalized air-kerma calibration coefficients, N K, measured with the proof-of-concept low-Z microchamber biased to +300 V (negative charge collection) for photon beams with effective energies ranging from 19.8 to 145 keV. Each N K value is normalized to the N K value measured in the M250 beam during each measurement set. The uncertainty at the k = 2 level for the N K measurements was 1.5%.
Each ionization chamber model used in this work and the corresponding collecting volume, the inner diameter (ID) and outer diameter (OD) of the wall, the OD of the collecting electrode, and the thickness of the build-up cap. The materials are PMMA, graphite (Gr), aluminum (Al), air equivalent plastic (C552), steel, and silver-plated copper-clad steel (SPC).
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