Re-calculation of air kerma to dose-equivalent conversion coefficients for mono-energetic photons

This work presents new calculations of conversion coefficients (CCs) from total air kerma to dose-equivalent quantities H’(0.07), H’(3), H*(10), H_p(0.07), H_p(3), and H_p(10) for area and personal dosimetry for mono-energetic photons in the energy range from 2 keV to 50 MeV, assuming secondary charged particle equilibrium. Calculations using the Monte Carlo N-Particle® (MCNP) code were performed for a large number of photon energies with the aim of preventing errors resulting from possible improper interpolation between currently available sparsely spaced CC values, when an average CC value over a photon fluence spectrum needs to be determined. The CC values were compared with the values published in the ISO 4037-3:2019 standard. A very close agreement was achieved for the majority of CCs. Larger discrepancies were found for some CCs, often for low photon energies or large angles of radiation incidence, which were taken from older publications or when CC values were interpolated or extrapolated. Furthermore, some differences were found in the MeV energy range, which are significant for dosimeter calibrations, e.g. the presented values of CC to H*(10) for the main photon energies of ¹³⁷Cs and ⁶⁰Co radionuclides are both lower by 2.8%. Finally, it was found that the values of CCs to H_p(0.07; E, α)_slab given in ISO 4037-3:2019 were not taken correctly from the source publication. In conclusion, the CC values given in ISO 4037-3:2019 should be updated in view of the results obtained.