Worldwide Open Proficiency Test: Determination of ... - Nucleus - IAEA

For homogenising the spiked water, a pump with multiple outlets was used to mix the water
in a tank of 600 litre. The homogenised spiked water was bottled in 500 ml portions in
appropriate plastic bottles. The total mass of the bottle with the label was registered for
further control. Three water sample portions at 100 g were analysed by gamma spectrometry.
The relative standard deviation of each analyte was calculated. It was found that the relative
standard deviations of all analytes were below the method repeatability relative standard
deviation, which demonstrates satisfactory homogeneity of the water sample.
Table 2 lists the target values and the associated combined uncertainty in the water samples.
TABLE 1. IDENTIFICATION OF THE CERTIFIED SOLUTIONS OF EACH RADIONUCLIDE USED IN
SPIKING THE WATER SAMPLES IN THIS PT
Draft, page 6
Nuclide Manufacturer code Source manufacturer
Co-57 9031-OL-090/09 Czech Metrological Institute
Co-60 Co60-ELSB50 Cerca
Cs-134 Cs134ELSR50 Cerca
Cs-137 CDZ64/S4/14/70 Amersham
Eu-152 Eu152-ELMB90 Cerca
TABLE 2. TARGET VALUES AND RESPECTIVE COMBINED STANDARD UNCERTAINTIES OF THE
RADIONUCLIDES OF INTEREST IN WATER SAMPLES
Analytes
Water Samples
02 and 04
Activity
(Bq/kg)
Uncertainty
(Bq/kg)
Water Sample
03
Activity
(Bq/kg)
Uncertainty
(Bq/kg)
MAB
(%)
Co-57 7.5 0.15 2.5 0.05 10 10
Co-60 6.0 0.12 2.1 0.04 10 10
Cs-134 13.9 0.28 4.6 0.1 10 10
Cs-137 9.5 0.19 3.2 0.06 10 10
Eu-152 11.3 0.23 3.7 0.08 10 10
For all measurement results the reference date is 15 November 2009, the combined standard
measurement result uncertainty is expressed at 1σ level.
2.3.2. Verification of the target activity values and homogeneity test
The final target activity value in water samples for each radionuclide was calculated from the
certified activity values assigned to each radionuclide, taking into account the successive
gravimetric dilution steps, the mass of spiking mixture and the amount of water being spiked
as determined from weighing. The combined standard uncertainty includes two major
components: uncertainty of the certified solution and weighing uncertainty.
LAP
(%)