Abstract: In order to achieve the accurate measurement of diagnostic level X-ray dose rate value, and to carry out the traceability and transmission of it, this article established a tube voltage of 40-150 kV and dose rate of 1.0×10^-3-10 Gy/h X-ray air kernal energy (diagnostic level) standard device according to the requirements IEC 61267—2005 standard, experimental measurement gives out the radiation field characteristics under different radiation qualities, and relative expanded uncertainty of air kernal energy rate in radiation field getting by evaluation. Experimental measurement results show that the radiation quality of RQR 5,while in a distance of 1.0 m from focal point of the X-ray spot, uniformity of radiation field >99.0% is ø8.0 cm, and uniformity >95.0% is ø10.0 cm; the contribution of scattering to radiation field is <0.9%; it is less than 2.0% about inverse square of the distance in the range of 1.0-5.0 m; the repeatability of radiation dose rate measured by the standard ionization chamber is 0.1%. Radiation qualities with RQR2-RQR10 series and RQT8-RQT10 are measured in HVL and homogeneity coefficient, which HVL deviation does not exceed ±0.09 mm, and homogeneity coefficient deviation does not exceed ±0.02. The evaluation result of relative expanded uncertainty in radiation field air kernal energy rate is U_rel=3.8%(k=2). Experimental measurement results of radiation quality characteristics show that the performance indicators of X-ray air kerma (diagnostic level) standard device meet the requirements of standards such as IEC 61267—2005.

Key words: diagnostic level, air kerma rate, half-value layer, uniformity, uncertainty