Conversion Coefficients from Kerma to Ambient Dose and Personal Dose for X-Ray Spectra

In radiation protection, the protection quantity for whole-body exposure is effective dose $E$. Effective dose cannot be measured and operational quantities have been introduced for dose measurement and calibration of dosimeters and survey instruments. To overcome some shortcomings of the presently used operational quantities, ICRU Report Committee 26 introduces two new quantities for whole body exposure, ambient dose $H^*$ for prospective dose assessment and personal dose $H_p(\alpha)$ for retrospective measurements with personal dosimeters. Dosimeters and survey instruments are calibrated in reference fields, realised with radioisotopes and with well-defined x-ray spectra. In this paper, the spectrum-averaged conversion coefficients from kerma in air $K_a$ to the new quantities ambient dose and personal dose are calculated and compared with the published coefficients for the present operational quantities. Especially at low energies ($E_{ph}$ < 40 keV), the new quantities are significantly lower than the present ones, thus correcting a strong overestimate of effective dose.