65 percent of worlds nuclear laboratories get Strontium 90 measurement wrong –
“The determination of 90Sr proved difficult for 65 % of the participants which submitted results outside the acceptable range (± 20 %). No improvement could be seen compared to 90Sr determination in one of the previous ILC exercises (Wätjen et al., 2008).
The laboratories concerned, i.e. the vast majority of laboratories reporting 90Sr results, are urged to review their analysis procedures.”
Joint Research Centre
Institute for Reference Materials and Measurements
Report on the JRC comparison of labs performance to measure radioactivity in soil
The JRC’s Institute for Reference Materials and Measurements (IRMM) organised an interlaboratory comparison (ILC) for the determination of 15 natural and anthropogenic radionuclides in soil. A report describing in detail all the phases of this exercise has just been published.
The Euratom Treaty obliges EU countries to perform measurements of the radioactivity in their environment and to report the results to the European Commission (EC). In order to verify the performance of monitoring laboratories and to ensure the comparability of reported results, regular interlaboratory comparisons were introduced by EC. Since 2003, JRC-IRMM is responsible for their organisation.
A total of 73 laboratories (49 from EU27, 7 from associated countries, 2 from Switzerland and 15 worldwide) completed the exercise. They were nominated among those laboratories that monitor radioactivity in the environment and foodstuff by national representatives in the expert group (Euratom Treaty Art. 35/36) and by the International Atomic Energy Agency (IAEA).
The certified reference material IAEA-375 Soil (originating from the area affected by the Chernobyl accident) was used as basis for the testing material, although it was made unrecognizable for the participants. Laboratories were asked to determine the level of the activity concentration of radioisotopes of potassium, strontium, caesium, lead, radium, bismuth, thorium, uranium and plutonium (40K, 90Sr, 137Cs, 212Pb, 212Bi, 214Pb, 214Bi, 226Ra, 230Th,232Th, 234U, 235U, 238U, 238Pu, and 239 240Pu).
The performance of the participating laboratories varied depending on the radionuclide determined and method used. Gamma-ray spectrometry of 137Cs and 40K was very successful. The determination of 90Sr proved difficult for about two-thirds of the participants, who submitted results outside the acceptable range. These laboratories need to improve their analytical procedures for 90Sr, as need several others for the uranium isotopes and 226Ra.
Link to report here- PDF
Soil from an area affected by the Chernobyl accident was used as comparison material in
this interlaboratory comparison. The reference values traceable to SI units were determined
at IRMM. The performance of 73 participating laboratories varied depending on the
radionuclide determined and method used (Table 20). With a few exceptions, the comparison
samples were treated and measured with routine procedures.
Gamma-ray spectrometry with respect to 137Cs and 40K is relatively well controlled in the laboratories. The determination of 90Sr proved difficult for 65 % of the participants which submitted results outside the acceptable range (± 20 %). No improvement could be seen compared to 90Sr determination in one of the previous ILC exercises (Wätjen et al., 2008).
The laboratories concerned, i.e. the vast majority of laboratories reporting 90Sr results, are urged to review their analysis procedures. The results clearly demonstrate that several laboratories need to improve their analytical procedures for determination of uranium isotopes. Mainly results of 235U proved to be highly method dependent when gamma-ray spectrometry rendered very poor results. This is most probably due to the lack of application of appropriate corrections in these measurements. A similar situation was observed fo r226Ra with unsatisfactory scores for gamma-ray spectrometry results and most probably caused by
similar reasons as in the case of 235U. Surprisingly, in the case of 232Th the results of gammaray spectrometry are significantly better compared to alpha-particle spectrometry results. However, the performance is more or less equal for both measurement methods for 230Th. One of the laboratories (lab 72) reported a result of 235U 50-times larger than the reference value. Also the results of 40K and 226Ra were overestimated by a factor of 2.1 and 1.7,
respectively, by the same participant (lab 72), while the result of 137Cs was underestimated by almost 40 %. Similar mediocre performance is observed also for other participants (labs: 39, 14, 44). These observations are distressing and indicate that critical and prompt revision of the measurement methods is necessary in these laboratories. Performance evaluation based on the En criterion revealed that uncertainty estimation is
unsatisfactory in many laboratories and there is a need to improve their application of uncertainty propagation and implement the concept of the GUM (2008).
The results of this ILC have shown again that proficiency testing with comparison samples
bearing reference values traceable to SI units (and SIR, where applicable) remains an
important tool to evaluate laboratory performance. More efforts on the side of the
participating laboratories are expected to turn bad ILC performance into improvement
actions, leading to the revision of existing, obviously insufficient laboratory routines. It must
be stressed that – as in any other application – only reliable methods should be used in
environmental monitoring, and gamma-ray spectrometry must be applied with the greatest care when it comes to naturally occurring radionuclide material (NORM).
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