  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.
