Abstract
Operational quantities in radiation protection are defined as conservative estimates of the protection quantities, which are generally not accessible to measurement. Radiation protection dosimeters and monitors are calibrated in the operational quantities. An ICRU Report Committee works on a proposal to replace the operational quantities for external radiation ambient dose equivalent, H*(10) and personal dose equivalent Hp(d, α) by quantities which are defined in close relation to the protection quantities. In this note, the response of dosimeters and survey instruments for photon radiation to these new operational quantities is evaluated. Survey instruments, having a low-energy cut-off at 50 keV can simply be recalibrated in the new quantity ambient dose and function as usual. Personal dosimeters will show an overreponse to photons with energy below 50 keV and either the dosimeter holder or the evaluation algorithm must be adapted to the new quantity.
Highlights
The ICRU has tasked Report Committee 26 to propose a redefinition of operational quantities [4], [5]
To overcome the shortcomings of the presently introduced operational quantities for external radiation, ICRU Report Committee 26 proposes new operational quantities which are closely related to the protection quantities by using the same phantoms for the calculation of conversion coefficients
From the limited range of investigated instruments in this note, three observations can be made: 1.) Survey instruments calibrated in ambient dose equivalent H*(10) can be recalibrated in ambient dose H* and show very similar response characteristics, owing to the sensitivity cut-off for energies Ep < 50 keV
Summary
Radiation protection dosimeters and survey instruments for photons are calibrated with reference radiations from X-ray generators and from radioisotope sources, described in standard. The Narrow-spectrum series is often employed for this purpose. Kerma-to dose conversion coefficients for these spectra are tabulated for the present operational quantities. The conversion coefficient ck(S) from kerma to a quantity C for a radiation quality S with fluence spectrum can be calculated by the expression. Where are the monoenergetic conversion coefficients from kerma to quantity C. Standards laboratory PTB makes fluence spectra and kerma-weighted fluence spectra available on its website [10], with these data the conversion coefficients from kerma to H*, Hp and Dlocal skin were calculated for the X-ray spectra of the Narrow-spectrum series according to Equation 2.
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