60Co and 137Cs gamma ray reference radiation field and the standard cavity ionization chambers used for air Kerma determination

60Co and 137Cs gamma ray reference radiation field has been established and a series of spherical graphite cavity chambers of different volume for 60Co and 137Cs gamma ray air Kerma determination have been developed. For 30 cm3 and 50 cm3 chambers, the total uncertainty is evaluated to be 0.74%, which is in good agreement with the national exposure standards and within 1% as compared with Japanese National Standard in Electrotechnical Laboratory (ETL) for both 60Co and 137Cs. The reference radiation beams used for radiation protection dosimeters' calibration in the laboratory are measured with these chambers. The results consist with that of the measurement in 1991 within 2%