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Radiation Protection Dosimetry 28:53-57 (1989)
© 1989 Oxford University Press
Techniques for Evaluating Conversion Coefficients to the New Dose Equivalent Quantities at a Calibration Laboratory
The Swedish authority for radiation protection, SSI, recommends the use of ambient and directional dose equivalents for environmental monitoring. To be able to offer calibration services, conversion coefficients for the low rate X ray radiation qualities recommended by the ISO in its report 4037 have been evaluated in a few different ways. The radiation qualities were determined both in terms of half value layers (HVL) and photon fluence distributions and conversion coefficients from air kerma to the new dose equivalents were calculated. The HVL measurements confirmed observations reported by others that the HVL values in practice deviate from those in the ISO report. The spectral distributions were measured with a HPGe semiconductor detector and the spectra were corrected to show the actual spectral distribution in air. The ambient and directional dose equivalents were then calculated using conversion factors from ICRP and analytical functions from Wagner et al. The two sets of data gave results that agreed within 2%. For calibrating laboratories a fluence distribution measurement technique may not always be available or practicable to use. Conversion factors calculated from effective and mean photon energy of the X ray beams were therefore compared with those derived above and agreed within 4% with those obtained when the whole photon fluence distributions were considered.