Establishing an independent measurement traceability for 60-Co Air Kerma

An independent air kerma traceability chain for $^{60}$Co radiation protection levels has been successfully established at the CIEMAT Ionizing Radiation Metrology Laboratory (LMRI-CIEMAT), based on the reference provided by the $^{137}$Cs primary standard. To achieve this, a secondary standard ionization chamber with an appropriate energy response was characterized, and its beam-quality correction factor, $k_Q$, was accurately determined via Monte Carlo simulations using the EGSnrc code. The method's accuracy was validated through a comparison with long-term historical calibration data and peer-confirmed through CIEMAT's successful participation in the EURAMET.RI(I)-S19 supplementary comparison, recently officially published in the BIPM KCDB. The excellent agreement achieved with international reference values demonstrates the high robustness and traceability independence of this newly implemented methodology.