X-ray spectrometry with germanium detector at a dosimetry calibration laboratory

Implementation of the recommendations of the new version of the ISO 4037 standard at X-ray installations of dosimetry calibration laboratories proved to be difficult and the uncertainties on the conversion coefficients due to differences between the fluence spectra from different installations are not yet sufficiently established. The X-ray installation of SCK CEN/LNK was characterized to verify the conformity with the most recent version of the ISO 4037 standard. The Half-Value Layer (HVL) values were measured to prove that conditions for matched beam qualities are fulfilled and then photon spectrometry with a High Purity Germanium (HPGe) detector was performed to measure the fluence spectra. Using the fluence spectra, the conversion coefficients from air kerma K_a to operational quantities were calculated and compared with the recommended values from the ISO 4037 standard. Most of these coefficients agree within 2% while the ISO 4037 recommended values have an uncertainty of 4% (k = 2). Possible sources of uncertainty in the photon spectrometry were evaluated and are discussed.