Key comparison BIPM.RI(I)-K7 of the air-kerma standards of the NMIJ, Japan and the NIM in mammography x-rays

The National Institute of Metrology, China(NIM) and the National Metrology Institute of Japan (NMIJ) conducted an international comparison of air kerma in the range of 25-35 KV of mammography. The measurement comparison uses an indirect comparison method. The National Institute of Metrology, as the leading laboratory, uses the molybdenum target reference free air ionization chamber to perform absolute measurement of (25~35) KV X-ray air kerma, and then under the same conditions. Pass the ionization chamber for calibration and give the scale factor. The ionization chamber is then calibrated in the radiation field of the other laboratory. The transfer ionization chamber was measured using a flat ionization chamber RC6M10167 from December 2018 to January 2018 under BIPM reference conditions. The deviation of the comparison results is between 0.3% and 0.4%.1