Abstract
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 Hp(α) 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 Ka 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 (Eph < 40 keV), the new quantities are significantly lower than the present ones, thus correcting a strong overestimate of effective dose.
Highlights
Effective dose cannot be measured and operational quantities have been introduced for dose measurement and calibration of dosimeters and survey instruments
Dosimeters and survey instruments are calibrated in reference fields, realised with radioisotopes and with welldefined X-ray spectra
The fluence spectrum is normalised to unit fluence (1 cm−2) and both dose-weighted spectra are normalised to the integral of the present operational quantity ∫ φSEp Ep kφ Ep hk∗ (10, E) dEp. The purpose of these figures is to illustrate how different parts of the spectrum contribute to the operational quantity, and how the change to the new quantity will lead to lower conversion coefficients, especially for low X-ray tube voltages
Summary
For the numerical evaluation of (2.1) with tabulated data the integrals must be discretised. The X-ray spectra from PTB [13] are tabulated with a resolution between 0.2 keV and 1.0 keV. The conversion coefficients were interpolated by a cubic spline function on a logarithmic energy scale to match the resolution of the X-ray spectra. For this purpose, the scipy [14] library routine interpolate.interp1d was used. The conversion coefficients for H∗(10) and Hp(10, α) were calculated with the algorithm described above and compared with the results published in [12]. For X-ray spectra with the lowest tube voltages, for example N10, deviations of up to 4.5% are observed, owing to the different interpolation- and integration algorithms
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