There were 4850 measurement results reported to the IAEA in this PT from 270 laboratories in 75 countries. The participants’ data along with the statistical performance evaluation were compiled and presented in two tables which constitute an integral part of this report.
Appendix I shows a summary evaluation for each laboratory and an extraction of the reported information in the PT questionnaire regarding the applied analytical technique. Performance evaluation tables sorted by analyte are reported in Appendix II. The S-shape and Z-score charts of evaluated analytes are presented in Appendix III, list of participants in Appendix IV.
The overall evaluation showed that 69% of all reported results fulfilled the PT criteria.
Table 4.1 shows the distribution of results scored as acceptable/warning/not acceptable for all evaluated nuclides.
The results’ evaluation shows that there are no specific measurement problems for K-40, Mn-54, Co-60, Zn-65, Cs-134, Cs-137, and Am-241.
4.2. Results of Cd-109 analysis
In the case of Cd-109 in soil only 42% of all reported results respectively were in agreement with the IAEA target values. The analytical problem in determination of this nuclide is persisting. However, 59% of reported “not acceptable” results in 2006 PT were improved to
“acceptable or warning” status, which indicate an important improvement in the Cd-109 quality of results.
It is known that, the main reason for the “Not Acceptable” scores in Cd-109 results could be attributed to the overestimation of peak area due to unresolved interference around the region of the 88 keV in a densely populated X-ray region which is difficult to resolve. The Cd-109 was the most problematic nuclide.
4.3. Results of Pb-210 analysis
Pb-210 was also a problematic nuclide, where results show a significant bias and incomparability among the laboratories. Comparing the performance for this analyte in 2006 and 2007 it was found that 55% of reported “not acceptable” results in 2006 PT were improved to “acceptable or warning” status, which indicates also an improvement in the quality of the Pb-210 measurement results.
It is suggested that the major sources of bias and incomparability in Pb-210 results could be attributed to the inappropriate detector calibration and/or the overestimation or underestimation of the self attenuation factor. As an example of practical approach for self absorption correction the approach suggested by Cutshall, Larsen and Olsen [8]. In certain laboratories the efficiency calibration was extrapolated, which led to large discrepancies.
4.4. Technical information provided by the participants
Appendix I contains the summary evaluation of each laboratory along with the summary of
the reported technical information. For each laboratory, Appendix I lists the radionuclides
which did not pass the test and which should be investigated for corrective actions.
TABLE 4.1. SUMMARY EVALUATION OF ALL NUCLIDES IN THE THREE SAMPLES
No. of reported results “Acceptable” results(%) “Warning” results (%) “Not Acceptable” results Nuclide (%)
soil water spinach soil water spinach soil water spinach soil water spinach K-40 - - 256 - - 72 - - 6 - - 22 Mn-54 268 263 - 75 69 - 8 10 - 17 21 - Co-60 267 263 - 80 76 - 8 8 - 12 16 - Zn-65 262 259 - 74 70 - 7 10 - 19 20 - Sr-90 - - 95 - - 53 - - 16 - - 31 Cd-109 242 234 - 48 66 - 5 11 - 47 23 - Cs-134 267 262 - 71 54 - 10 11 - 19 35 - Cs-137 270 266 258 79 78 78 9 9 5 12 13 17 Pb-210 158 168 - 54 62 - 11 9 - 35 29 U-234 - - 72 - - 60 - - 8 - - 32 U-238 - - 76 - - 57 - - 9 - - 34 Pu-238 - - 54 - - 67 - - - - - 33 Pu-239+240 - - 62 - - 65 - - - - - 35 Am-241 240 231 57 72 72 37 10 9 - 18 19 33
From Appendix I it can be found that the majority of the participating laboratories calibrated their system using multi gamma standard source. There was no significant difference observed between the percentage of acceptable results of the laboratories which used multi gamma standard source and those which used computational approach.
4.5. Recommendations to the laboratories
Based on the performance evaluation results the participating laboratories could be distributed into five groups, Figure 4.24 shows this distribution.
4.5.1. Laboratories group A
Thirty-four laboratories reported their results without any “not acceptable” score. Table 4.2
lists the codes of these laboratories. Only one participant lab code 189 reported all the
analytes (24 results) and obtained 100% acceptable results. Participants with codes 12,104,
116, 144, 202, 229, 288 and 311 reported few of the α, β emitting radionuclides. It is
recommended to this group of laboratory to maintain the statistical control of the analytical
process and to monitor it. This group of laboratories reported satisfactory analytical results for
the scope and evaluation criteria of this PT.
TABLE 4.2. LABORATORIES GROUPS ACCORDING TO THE ANALYTICAL PERFORMANCE
Group Laboratory code
Group A
4, 10, 12, 53, 55, 70, 88, 104, 111, 116, 121, 128, 133, 144, 145, 149, 178, 189, 202, 209, 210, 229, 245,259, 263, 264, 271, 272, 273,
275, 288, 292, 307, 311
Group B
15, 20, 24, 25, 29, 34, 35, 43, 48, 51, 56, 63, 64, 77, 82, 105, 107, 110, 112, 113, 115, 134, 140, 143, 155,187, 188, 196, 199, 200, 203,
215,218, 226, 227, 234, 237, 249, 252,269, 287, 304, 312, 318 7, 8, 13, 28, 49, 62, 65, 78, 84, 90, 97, 119, 131, 138, 139, 142, 160, 161,166, 186, 190, 207, 214, 224, 254,257, 260, 261, 262, 265, 285,
290,293, 296, 297, 310, 317, 319, 322
Group C
2, 6, 14, 33, 36, 44, 67, 87, 93, 99, 101, 117, 126, 135, 137, 150, 156,174, 177, 192, 201, 228, 233, 235, 238, 239, 242, 244, 250, 253,
295
5, 9, 11, 19, 76, 120, 122, 124, 146, 147, 163, 204, 208, 240, 241, 277, 278, 291, 299, 305, 316
Group D
3, 18, 23, 27, 31, 59, 71, 86, 123, 154, 169, 172, 184, 197, 213, 217, 222, 225, 270, 280, 321
1, 45, 60, 69, 92, 157, 158, 185, 198, 220, 248, 286, 320
21, 37, 73, 75, 114, 125, 127, 130, 162, 164, 165, 168, 173, 179, 206, 212, 223, 230, 268, 281, 300, 302, 306
Group E
50, 148, 151, 152, 246, 255, 256, 258 80, 81, 85, 175, 236, 251, 284, 309 26, 30, 42, 103, 153, 167, 182, 16, 39, 95, 98, 118, 132, 191, 231,308
91, 96, 129, 232 79, 89, 108, 195, 243
4.5.2. Laboratories group B
Forty-five and thirty-nine laboratories had only one or two “not acceptable” results respectively.
The not acceptable performance mainly due to Cd-109, Cs-134 and Pb-210 and partially due to α and β emitting radionuclides.
The results of Cd-109 in water reported by this group were in general acceptable, in contrary
to the results of the same analyte in soil, which indicates that the matrix effect correction still
has to be optimized.
The quality of reported results, by this group of laboratories, fits the criteria of this PT However, further investigation should be undertaken to investigate the root cause of the specific nuclide shortcoming and corrective action should be applied to rectify the situation.
4.5.3. Laboratories groups C and D
In group C thirty-one and twenty-one laboratories scored three or four “not acceptable” results respectively. Group D combines laboratories which scored 5-8 “not acceptable” results.
These laboratories reported acceptable results for the regularly and more common nuclides, the root cause of not acceptable performance should be investigated and corrective actions to be implemented.
0 10 20 30 40 50 60 70 80 90
0 group A
1-2 group B
3-4 group C
5-7 group D
> 8 group E Number of not acceptable scores
Number of laboratories
Fig. 4.24: Laboratories’ grouping according to their performance.
4.5.4. Laboratories group E
This group of laboratories scored more than 9 “not acceptable” results. The quality control mechanism should be revised in these laboratories, efficiency calibration should be validated using matrix reference materials and the statistical control of the analytical system should be checked at regular intervals.
The analyst should set up a procedure to check the validity of each produced result either using in-house reference material for precision control or using spiked matrix material to check the trueness of the measurement results. The calibration standard should contain the same analytes of interest if possible, or single standard solutions should be used to check the applied corrections and the efficiency calibration.
It is recommended to reanalyse the PT samples after the introduction of the appropriate
corrective actions and to check if the target values were obtained. The Chemistry Unit at
Seibersdorf Laboratories is ready to provide the participants with the technical advice upon a
specific request from the participants of this group.
4.6. Comparison of participants performance in 2006 PT and 2007 PT
There were 175 laboratories that participated in the 2006 and 2007 proficiency tests. From the stored data it was possible to track the performance of the laboratories for each analyte. The
“not acceptable” results reported by this group of participants were tracked and compared.
From the comparison it was found that in average more than 60% of “not acceptable” results reported in 2006 PT were improved to “acceptable” or “warning” status (see Table 4.3). This clearly suggests that most of the participants were able to identify the analytical problem occurred during the participation in the 2006 PT and were able to improve their performance in the current PT.
In the contrary, some of the participants were not able to keep their good performance demonstrated in the 2006 PT and the quality of their reported results in 2007 was worse than those reported in 2006. Around 15% of the reported results by the 2006 PT participants moved down from “acceptable” in 2006 to “not acceptable”. This suggests that one shot of participation in a PT is not a sufficient evidence for a good and stable performance, only continuous participation in PTs demonstrates the stability of the analytical system performance.
Table 4.3 shows the percentage of positive or negative development of the analytical performance per analyte.
TABLE 4.3. COMPARISON OF ANALYTICAL PERFORMANCE BETWEEN THE TWO PTS IN 2006 AND 2007
Positive Development From “N” in 2006 PT to “A” in
2007 PT
Negative Development From “A” in 2006 PT to “N” in
2007 PT
Am-241 78.2 10
Cd-109 59.0 22.6
Co-60 67.5 6.1
Cs-134 67.6 16.9
Cs-137 74.2 7.4
K-40 76.7 17.9
Mn-54 59.7 8.3
Pb-210 54.9 20.4
Zn-65 70.5 12.4
Dans le document
Worldwide Open Proficiency Test on the Determination of Radionuclides in Spinach, Soil and Water | IAEA
(Page 30-35)