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The recent participation of IFIN-HH/Ionizing Radiation Metrology Laboratory (LMRI) to the CCRI(II)-K2.Cd-109 comparison allowed to test four different installations from LMRI, used to perform absolute and relative activity standardizations: LSC, 4πγ well type Ionization Chamber (IC), HPGe γ-ray spectrometry system and Si(Li) X-ray spectrometry system. The present paper refers to the three installations for relative measurements, often used to calibrate radioactive sources and solutions for the customers of the LMRI accredited laboratory. Based on the 4π-LS-CE method applied with the LSC equipment, the absolute activity concentration of the Cd-109 solution was determined with a low relative combined uncertainty (less than 1%). This allowed us to test the two spectrometry systems by measuring the absolute intensity of low energy photons emitted following the Cd-109 decay: γ-rays of 88.03 keV and Kα and Kβ X-rays (Ag-109), using HPGe and Si(Li) spectrometry systems, respectively, calibrated with available radioactive standard sources combined with a detection efficiency transfer procedure by MC simulations (GESPECOR software). The Cd-109 sources measured were: an ampoule with 2.008 grams of solution and a point solid source (the solution was deposited gravimetrically on a polyethylene disk) – for the HPGe system, and a similar point solid source (solution deposited on a golded VYNS film) – for the Si(Li) system. For the 88 keV gamma-rays, the closest experimental calibration points on the rising part of the HPGe calibration curve were at 59.54 keV (Am-241) and 81 keV (Ba-133). It is difficult to characterize experimentally the low energy region of the HPGe detector calibration curve, because of the lack of standard sources and the high background in the gamma-ray spectrum. As a consequence, the emission intensity result for the 88 keV γ-rays, 0.0375 (9), has a high standard uncertainty, compared with the only three results published in the literature since 1990 (K. Kossert et al., 2006; G. Ratel, 1994 and U. Schötzig et al., 1991). The result is in agreement with the above-mentioned results and the most recent ENSDF (S. Kumar et al., 2016) and DDEP evaluations (0.0366 (5), by M.M. Bé, E. Schönfeld, Monographie BIPM-5, vol. 8, 2016). The calibration of the Si(Li) system was performed using standard sources of Co-57, Am-241, Fe-55, Cs-137. The results obtained in the analysis of the X-rays (Ag-109) will be presented and discussed in this paper. The activity concentration of the Cd-109 solution received from the BIPM was measured with the IC calibrated for Cd-109 and other radionuclides at PTB (2001). The activity concentration result is significantly lower than the values given by the other two methods mentioned above. The reasons are analyzed, in order to test the IC method limitations for low energy photons, low activity and low gamma-ray emission intensities. For all the measurements results presented, detailed uncertainty budgets are provided.
