Spectrometry of the X-ray facilities of 6.3 and redefinition of the conversion coefficient for radiation protection quantities

The photon spectra of the 120 kV and 400 kV X‑ray facilities of Department 6.3 were characterized using two independent detector systems. The fluence spectra of the respective radiation qualities were obtained from the unfolded measured pulse height spectra. Using these fluence spectra, the conversion coefficients including their uncertainties were redefined for the different radiation protection quantities for tissue depths of 0.07 mm, 3 mm and 10 mm. The figure shows an example of the uncertainties (coverage factor k = 1) for H_p(d) for the N-, W- and H-series as per ISO 4037-1 and tissue depths of d = 0.07 mm, d = 3 mm and d = 10 mm as a function of the generator voltage U_gen, measured at the 120 kV X‑ray facility at a distance of 2.5 m from the X‑ray tube’s focus. The reason for the relatively high uncertainties of the conversion coefficients H_p(d) for d = 3 mm and d = 10 mm at generator voltages of U_gen ≤ 20 kV is the pronounced energy dependence of the respective monoenergetic conversion coefficients in the low energy photon range. Even minor differences in the detectors’ energy calibration lead to considerable differences in the conversion coefficients.

Figure: Uncertainties (coverage factor k = 1) for H_p(d) for the N-, W- and H-series and tissue depths of d = 0,07 mm, d = 3 mm and d = 10 mm as a function of the generator voltage U_gen, measured at the 120 kV X‑ray facility at a distance of 2.5 m from the X‑ray tube’s focus.

Contact

G. Hilgers, Department 6.3, Working Group 6.31