RESEARCH ON THE ABSOLUTE MEASUREMENT AND CALIBRATION METHODS OF (250-450) KV X-RAY AIR KERMA AT NIM

With the rapid application of nuclear technology, radiation protection is becoming more and more important. For external radiation protection, most of the national metrology institutes in the world have established the primary standard of X-ray air kerma in (10-250) kV and Cs-137 gamma ray, but the energy between 250 and 662 keV needs the establishment of traceability. To provide solution to such issue, a graphite cavity ionization chamber was constructed at National Institute of Metrology to measure the air kerma in (250-450) kV X-ray. The relative standard uncertainty of the method is 0.45%. Two different types of ionization chambers were used to measure the air kerma of N-300 radiation quality, and the result has a deviation of 0.09%.