Measurement of (55)Fe solution activity by LSC-TDCR method.

A solution of (55)Fe was measured by using liquid scintillation counting (LSC)-TDCR method. The measurement was performed within the frame of the CIPM CCRI(II)-K2.Fe-55 comparison during the year 2006. Two computation codes were used for the calculation of detection efficiency, the difference between the results being analyzed. The photomultipliers asymmetry and its influence on the results, as well as the long-term stability are also analyzed. The influence of the variation of kB value over the activity value is compared with the case of (3)H standardization.

The IFIN-HH triple coincidence liquid scintillation counter.

The paper summarizes the IFIN-HH triple coincidence liquid scintillation counter used for the implementation of the TDCR method. The electronic unit was recently extended to record the three individual double coincidence ratios to take into account the differences in the quantum efficiencies of the three-photomultiplier tubes. Some details of the electronic system and the data processing are given. The critical point of a TDCR counter is to adjust correctly the discriminator levels on the three channels under the single electron peak. The paper describes the method of adjustment based on the evolution of the dark counting rate versus the discriminator level. Also indicated is the influence of the discrimination level on the activity results as measured at IFIN-HH using a 3H standard. The performances of the IFIN-HH TDCR counter was checked against the measurement results of the TDCR counters of CSIR NML (South Africa), RC (Poland) and LNHB (France). A set of ready-to-measure 63Ni sources in liquid scintillator, in sealed counting vials, was prepared and dispatched for measurement to all these laboratories. The paper describes designs of the TDCR counters used. An analysis and discussion of the measurement results is given.

Results obtained in the metrological certification of a commercially available radionuclide calibrator.

The paper presents the results obtained at IFIN-HH during a metrological certification of the commercially available radionuclide calibrator, the CURIEMENTOR2. Its performance was tested for the radionuclides: 57Co, 99mTc, 131I and 137Cs. The calibration factors determined by the manufacturer and those obtained at IFIN-HH differed by less than 3.5%. New calibration factors were determined for 60Co and 188Re, which have, until now, not been distributed by the manufacturer to the users. Furthermore, the linearity of instrument response and the dependence of measuring geometry were checked and found in accordance with the international accepted standards and legal requirements.

The standardization of a 204Tl solution

Two methods were used for the standardization of the 204Tl solution received in the framework of the 1997 BIPM comparison. The first method, 4pi liquid scintillation (LS), consisted of the extrapolation of the 4pi counting rate to the zero discrimination level. A home-made, single channel instrument and a commercial Packard INSTA-GEL scintillator were used. The radioactivity concentration on the reference date 1 April 1997 was 63.1+/-1.3 kBq g(-1). The second method was the efficiency tracer technique, using a 60Co standard solution; the radioactivity concentration was calculated as the mean of several extrapolated values of the curve NbetaTl-204 = N0Tl-204f(1 - epsilon(betaCo-60)). The preliminary reported value was 62.8+/-0.8 kBq g(-1); the revised value is 61.8+/-1.2 kBq g(-1), in good agreement with other 4pi (p.c.) tracer results in the comparison. Some remarks are made regarding our measurements and the comparison results.