ARTICLE IN PRESS. Applied Radiation and Isotopes

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1 Applied Radiation and Isotopes 68 (1) 1 16 Contents lists available at ScienceDirect Applied Radiation and Isotopes journal homepage: EC comparison on the determination of 226 Ra, 2 Ra, 2 U and 8 U in water among European monitoring laboratories U. Wätjen a,, L. Benedik a,1, Y. Spasova a, M. Vasile a, T. Altzitzoglou a, M. Beyermann b a European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, B-24 Geel, Belgium b Bundesamt für Strahlenschutz (BfS), Köpenicker Allee 1-, D-1318 Berlin, Germany abstract In anticipation of new European requirements for monitoring radioactivity concentration in drinking water, IRMM organized an interlaboratory comparison on the determination of low levels of activity concentrations (about 1 1 mbq L 1 ) of the naturally occurring radionuclides 226 Ra, 2 Ra, 2 U and 8 U in three commercially available mineral waters. Using two or three different methods with traceability to the International System of Reference (SIR), the reference values of the water samples were determined prior to the proficiency test within combined standard uncertainties of the order of 3% 1%. An overview of radiochemical separation and measurement methods used by the 45 participating laboratories are given. The results of the participants are evaluated versus the reference values. Several of the participants results deviate by more than a factor of two from the reference values, in particular for the radium isotopes. Such erroneous analysis results may lead to a crucial omission of remedial actions on drinking water supplies or to economic loss by an unjustified action. & 9 Elsevier Ltd. All rights reserved. 1. Introduction The activity concentration of natural radionuclides in drinking water is quite variable, depending on the properties of the aquifer rock and the prevailing lithology. Whereas the radionuclide activity concentration in waters usually poses no health concern, there are regions in which the geological situation can render radioactivity levels which need to be monitored in order to reduce the potential health risk of the public. Concerns about the radioactivity concentration of water intended for human consumption have been described (Benedik et al., 8, 9), and a variety of regulations implemented (WHO, 1993, 6; European Communities, 1998, 1) to limit public exposure to radioactivity from drinking water. The European Atomic Energy Community (EURATOM) Treaty obliges the member states of the European Union to monitor and report the levels of environmental radioactivity on their territory. Some details of sample taking and measurement requirements (sample types, sampling intervals, radionuclides, etc.) are regulated at European level. In order to verify the quality and in particular comparability of the values reported by the member states, comparison exercises were introduced by the European Corresponding author. Tel.: ; fax: address: uwe.waetjen@ec.europa.eu (U. Wätjen). 1 Present address: Jožef Stefan Institute, Jamova 39, SI-11 Ljubljana, Slovenia. Commission after the reactor accident of Chernobyl. Since 3, the Institute for Reference Materials and Measurements (IRMM) had responsibility for their organization. The metrological approach of IRMM in conducting such comparisons using samples carrying reference values traceable to SI units and the International Reference System for g-ray emitting radionuclides (SIR) was presented at the most recent ICRM conference (Wätjen et al., 8). In anticipation of new requirements (European Communities, 1) for monitoring radioactivity in drinking water, IRMM has organized a comparison among member state laboratories requesting the determination of low levels of activity concentrations (around the detection limits prescribed in future legislation) of the naturally occurring radionuclides 226 Ra, 2 Ra, 2 U and 8 U in three commercially available mineral waters (W1, W2 and W3, the latter as two subbatches W3-5 and -51). 2. Determination of the reference values The reference values for these comparison samples (activity concentration) were determined by consensus between two independent expert laboratories according to clause 5.5 of the standard ISO 1 (ISO, 5) with the additional constraint that the analyses had to be performed in such a way that the determined values are traceable to SI units and the SIR (Wätjen et al., 8). IRMM and the Bundesamt für Strahlenschutz (BfS), Department for Radioprotection and the Environment, Berlin, as /$ - see front matter & 9 Elsevier Ltd. All rights reserved. doi:1.116/j.apradiso

2 U. Wätjen et al. / Applied Radiation and Isotopes 68 (1) expert laboratories applied two largely different, independent methods (three in the case of 2 Ra). Since the methods used to determine the reference values in these waters have only partly been published earlier ((Benedik et al., 8) for 226 Ra and uranium at IRMM; (Vasile et al., 9) for two methods of 2 Ra at IRMM), some complementary information is summarised here. A detailed account of the reference value determination is given in the comparison report (Spasova et al., 1) Determination of 2 U and 8 U At BfS, the determination of uranium isotopes was performed with proven methods of radiochemical separation and activity measurement (Bundesminister, 6). Whereas the radiochemical separation by extraction chromatography and the use of 2 U as a tracer is very similar to the method used at IRMM, the preconcentration consisted of evaporating water samples of 1 L to dryness and wet ashing of the residues. The thin sources for a- particle spectrometric measurement were prepared by electrodeposition on stainless steel discs (Spasova et al., 9) Determination of 226 Ra At BfS, the standardized radon emanation method H-Ra-226- TWASS-1-1 (Bundesminister, 6) was applied. Radium was preconcentrated by coprecipitation with BaSO 4 from water samples of 1 L, using the natural Ba carrier addition as a tracer by determination with atomic absorption spectroscopy. The precipitate was dissolved in EDTA/NH 4 OH and transferred to a radon bubbler. The sample was de-emanated and stored for a minimum of 14 days to allow 222 Rn to grow in. The grown-in 222 Rn was then transferred to a Lucas-type scintillation chamber, where the a-emission of 222 Rn and its short-lived decay products were counted. The system was calibrated with a 226 Ra standard solution Determination of 2 Ra At IRMM, two independent methods were applied. The first one is based on the procedure described by Nour et al. (4), using coprecipitation with MnO 2 for preconcentration of 2 Ra from water volumes of 1.5 and 3 L, in combination with liquidscintillation counting of the daughter nuclide 2 Ac. For the second method, use was made of sources prepared a year earlier for the determination of 226 Ra by a-particle spectrometry. The basic idea is to separate and determine by a-particle spectrometry the 2 Th grown in as granddaughter nuclide of 2 Ra after more than a year. 229 Th is used as tracer for determination of the chemical yield. Both procedures are described in detail in Vasile et al. (9). The BfS laboratory followed the standard procedure H-Ra-2- TWASS-1-1 (Bundesminister, 6). Adapted from Burnett et al. (1995), radium and actinium were preconcentrated by coprecipitation with barium sulfate, the sulfate was converted to a more soluble carbonate, and after a waiting time of at least 3 h the grown-in 2 Ac was separated by extraction chromatography on RE Spec resin. Sources were prepared using micro-coprecipitation of actinium on cerium fluoride, immediately followed by b-particle measurement in a low-level proportional counter. The chemical yield of the radium separation was determined via atomic absorption spectrometry of the barium carrier. The proportional counter was calibrated with a standardised 89 Sr source Homogeneity and stability Since the reference values of the comparison material must be valid for each bottle of a mineral water batch, the homogeneity of each batch, i.e., the variation, s bb, of the nuclide activity concentration between bottles of the batch, are determined by random test. Any heterogeneity found contributes to the combined uncertainty of the corresponding reference value. A similar study is performed for the short term stability, u sts, of the samples. In the case of bottled mineral waters, adsorption of radionuclides to the container walls may limit its stability (i.e. the availability of radionuclides for analysis). Thus, the expanded uncertainty, U ref (k=2), of the reference value can be estimated as qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi U ref ¼ k u 2 char þs2 bb þu2 sts; ð1þ where s bb and u sts are defined above, and u char is the combined standard uncertainty of the mean of measurement results from the two laboratories such that: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P n i ¼ 1 u char ¼ ðu c;iþ 2 ; ð2þ n where u c,i is the combined standard uncertainty of the laboratory s (or method s) result (Pauwels et al., 1998). In numerical terms, no wall adsorption could be found in the corresponding tests, hence u sts can be set to (Spasova et al., 9). In the homogeneity studies performed, values between 2% and 1% were found for the different waters and radionuclides (Benedik et al., 8; Spasova et al., 9). Table 1 gives all reference values with their expanded uncertainties, together with the separate laboratory means of activity concentration. 3. Methods used by the participating laboratories Participants were free to use separation procedures and measurement methods of their own choice. Of the 45 laboratories which reported results, not all determined all four radionuclides. Table 2 gives an overview of the measurement techniques used. Together with other details of this comparison, more complete information on the applied methods can be found in the comparison report (Spasova et al., 1) U and 8 U Thirtytwo laboratories used a-particle spectrometry for the determination of 2 U and, except in one case, of 8 U. All laboratories added isotopic tracer ( 2 U or, in one case, 6 U) in order to determine the radiochemical yield of the procedure. Except for one, all laboratories preconcentrated uranium from the water samples and carried out radiochemical separation from the matrix components. For preconcentration from water, nine laboratories applied evaporation and laboratories carried out co-precipitation, using phosphates (6 labs), Fe(OH) 3 (9 labs), and MnO 2 (2 labs), respectively. The radiochemical purification was performed with ion exchange chromatography, extraction chromatography and solvent extraction, respectively. Some laboratories used a combination of these techniques. Sources for a-particle spectroscopic measurement were prepared by electrodeposition ( labs), micro-coprecipitation with rare earth fluorides (9 labs), and micro-coprecipitation with cadmium chloride (1 lab), respectively. The four laboratories using g-ray spectrometry for 8 U evaporated the water and measured the dry residue directly. The activity concentration of 8 U was determined via 2 Th (at 63

3 U. Wätjen et al. / Applied Radiation and Isotopes 68 (1) 1 16 Table 1 Activity concentrations in mineral waters determined by the two laboratories, IRMM and BfS, and comparison reference values A ref calculated as mean of these results (reference date 1 May 6). Water Nuclide mean value with combined standard uncertainty u c Reference value A ref with expanded uncertainty U ref Activity concentration (mbq L 1 ) Activity concentration (mbq L 1 ) IRMM a IRMM second method b BfS W1 U U Ra Ra W2 U ( ) U (4.7.5) Ra Ra W3-5 U U Ra (3.67.8) Ra-2 o ( ) W3-51 U U Ra (3.67.8) Ra-2 o ( ) Values A ref given in brackets were not required to be determined by comparison participants. Uncertainties of laboratory results given as combined standard uncertainty u c, uncertainty of reference values as expanded uncertainty U ref =u k with a coverage factor k=2, corresponding to a level of confidence of about 95%. a 2 Ra via liquid-scintillation counting of 2 Ac. b via 2 Th ingrowth and a-spectrometry. Table 2 Number of participating laboratories reporting results and measurement techniques used for determining the four radionuclides. Radionuclide U-2 U-8 U tot Ra-226 Ra-2 Reported results all methods 2 Reported results by method: a-particle spectr. 31 a 3 a 11 1 (via 224 Ra) Gross-a counting 3 ICP-MS 1 1 g-ray spectr Radiochemical NAA 1 LSC 1 b 2 b 3 Fluorimetry Gross-b counting 4 Sorption emanation technique 9 a Plus one additional laboratory (Water-1 only). b Plus one additional laboratory (Water-3 only). and 93 kev), assuming equilibrium between 8 U and its progeny 2 Th. One laboratory determined 2 U bya-particle spectrometry and 8 U by radiochemical neutron activation analysis via its induced 9 U nuclide. One laboratory determined the uranium isotopes with inductively coupled plasma mass spectrometry (ICP-MS) from sample aliquots of 1 ml without additional sample preparation. Three laboratories used liquid-scintillation counting (LSC) in a/b-discrimination mode. Two laboratories determined total uranium using fluorimetry after evaporating the water samples and fusing the residues with a mixture of NaF and NaCO 3 at 9 1C; the activity concentration of 8 U was calculated assuming the average natural isotopic composition and that of 2 U based on the assumption of equilibrium Ra a-particle spectrometry was applied in eleven laboratories, all of which included the use of tracers. Laboratories used a large variety of coprecipitation techniques for preconcentration with MnO 2, Pb(NO 3 ) 2, BaSO 4, Fe(OH) 3, and Pb(CrO 4 ) 4, respectively. One laboratory determined 226 Ra directly from a Ra-adsorbing disc (MnO 2 ) which had been immersed into the sample for 6 h. Sources for a-spectrometric measurement were prepared by coprecipitation with BaSO 4 or BaCl 2, or by electrodeposition on stainless steel discs. The recoveries of the reported radiochemical procedures were determined with 3 Ba, 2 Ra (via its progeny 2 At), and 224 Ra, respectively. Six laboratories applied g-ray spectrometry; five evaporated the water samples (between 3 and L) to dryness and one laboratory preconcentrated radium by coprecipitation with BaSO 4. The residues after evaporation or the Ba(Ra)SO 4 precipitates were sealed, and 226 Ra was determined by the 1 and 69 kev g-ray lines of its 214 Pb and 214 Bi progenies after an ingrowth period of at least 3 weeks. Nine laboratories applied the sorption emanation technique similar to the procedure described above for BfS (see Section 2.2). Twelve laboratories measured samples, after different preconcentration procedures had been applied, by liquid-scintillation counting (LSC). Six laboratories coprecipitated radium with MnO 2, or as Ba(Ra)SO 4. The precipitate was purified with a variety of techniques to remove interfering radionuclides, dissolved and mixed with scintillation cocktail. In five of the six laboratories, the scintillation vial was tightly closed and stored for up to 1 month to allow ingrowth of 222 Rn and its daughters. One of these 6 laboratories measured radium immediately after sample preparation. Two laboratories of the remaining 6 freeze dried the original samples to preconcentrate, whereas two other laboratories thermally preconcentrated the samples, desorbing at the same time all dissolved radon, followed by the usual waiting time in scintillation vials. One laboratory mixed the sample with a

4 U. Wätjen et al. / Applied Radiation and Isotopes 68 (1) 1 16 Preconcentration Calcination (1 lab) Evaporation (~ 15 labs) - to dryness - to reduced volume Separation/purification Empore Radium Rad disk (2 labs) (1 lab) (2 labs) Extraction chromatography (3 labs) Coprecipitation with (2 labs) - BaSO 4 (9 labs) - lead sulphate (1) - Ca phosphomolybdate (1) - MnO 2 (1) Solvent extraction (TBP) (1 lab) Ion exchange resin (2 labs) direct measurement of water (1 lab) source preparation measurement (1 lab) Fig. 1. Summary of preconcentration and radiochemical separation procedures used for the determination of 2 Ra by the comparison participants Ra - W > (76) Fig. 2. Mean laboratory results for 226 Ra compared to reference value of activity concentration in Water-1. Error bars, if applicable, indicate the standard deviation s of the laboratory mean, solid and dashed lines are reference value A ref 7U ref (k=2). Encoded laboratory numbers are indicated. Values in brackets indicate measurement results falling outside the scale of the figure. mineral oil scintillator and measured directly by LSC. Another laboratory used the Empore Radium Rad disc and.1 M EDTA, which selectively extracts radium from an acidic solution. Three laboratories preconcentrated radium with lead sulphate and/or BaSO 4, and the determination of 226 Ra was carried out by measuring the gross-a activity of the Ba(Ra)SO 4 precipitate on a filter using a low-background gas proportional counter Ra About half of the laboratories evaporated the samples, to reduce volume or to dryness, as a preconcentration step. A bit fewer than half performed coprecipitation, with Ba(Ra)SO 4 as the most often formed precipitate. Some of the laboratories applied a combination of preconcentration procedures or added purification steps; Fig. 1 gives an overview of all methods used for 2 Ra. Not all laboratories determined the recovery of their concentration and purification procedures. Some used 3 Ba as a tracer, or stable Ba (in the form of added carrier) that was then determined by photometry or ICP-MS. The laboratory which determined 2 Ra via a-particle spectrometry of 224 Ra used 2 Ra in equilibrium with 229 Th as a tracer. A few laboratories used external standards ( 226 Ra, 2 Ra) or gravimetry to determine chemical yield. 4. Comparison results As far as the determination of radium is concerned, the results of the comparison are far from satisfactory. Fig. 2 shows that the values determined by many laboratories for 226 Ra in Water-1 were too low (up to a factor of 14), while two laboratories determined values too high (as much as up to 8 times the reference value). By contrast, the reference value determined by IRMM and BfS has a relative expanded uncertainty, U ref, of 15%. One should note that a 226 Ra activity concentration of 1 mbq L 1 in water is more than twice the limit of detection

5 14 U. Wätjen et al. / Applied Radiation and Isotopes 68 (1) 1 16 required by the EC draft directive, and measurement results five times too high or too low would result in unnecessary or omitted remedial action, respectively (cf. Table 3). It is not satisfactory that only 29 laboratories (out of ) are able to determine the 226 Ra activity concentration within % from the reference value. The results for 226 Ra in Water-2, although at lower activity concentration, reveal a similar, although slightly better performance (Fig. 3). Again, laboratories show results spread around Table 3 Reference concentrations a and required limits of detection proposed in the draft European Council Directive (European Communities, 1). Nuclide Reference concentration (Bq L 1 ) Detection limit (Bq L 1 ) U U Ra Ra a Reference concentrations refers to activity concentrations triggering under certain conditions and after taking account of summing effects remedial actions such as restrictions of use when surpassed. the reference value to within7%. The extreme deviations are, in this case, 6 times too low and a factor of 3 too high. Comparing laboratory numbers in Figs. 2 and 3, it appears that there is a group of laboratories with one (lab ) as an exception which incorrectly implement the chosen 226 Ra analysis procedures systematically. Even more problematic is laboratory performance in the determination of 2 Ra. In Water-2, there are only 14 laboratories (of 29 submitting results) that are within7% of the reference value without forming a distinct plateau of measurement results around the reference value (Fig. 4). Five laboratories determine values too low, and 1 submit results too high (by 4 %). The situation for 2 Ra in Water-1 (not shown) is similar; 16 laboratories, i.e., more than half, obtain results that are too high by 4%. One of the laboratories (no. 24) determines an excessively high activity concentration of 885 mbq L 1 (A ref = mbq L 1 ; U ref =6 mbq L 1 ; k=2) in Water-1, whereas its result for Water-2 is a factor of about 3 too low. This bad performance is unacceptable in the view of unnecessary or omitted remedial action resulting from such erratic analytical results Ra - W Fig. 3. Mean laboratory results for 226 Ra compared to reference value of activity concentration in Water-2. Error bars and indication of reference value as in Fig Ra - W Fig. 4. Mean laboratory results for 2 Ra compared to reference value of activity concentration in Water-2. Error bars and indication of reference value as in Fig. 2.

6 U. Wätjen et al. / Applied Radiation and Isotopes 68 (1) U - W > (92) 11 --> (1) Fig. 5. Mean laboratory results for 8 U compared to reference value of activity concentration in Water-1. Error bars and indication of reference value as in Fig. 2. In general, the analysis of uranium activity concentration in mineral water is much better controlled by the vast majority of participating laboratories. For example, Fig. 5 depicts the results for the determination of 8 U in Water-1. In this case, of laboratories obtain results within7% of the reference value; only two laboratories obtain results that are too low (maximum by 45%), and six laboratories report values 4% too high (in the two worst cases, by a factor of about 8 and 11, respectively). The comparison results for the determination of 2 U in both waters and 8 U in Water-3 are similarly acceptable. 5. Conclusions Three commercially available mineral waters were provided as comparison samples. The reference values for the natural radioactivity concentration of 226 Ra, 2 Ra, 2 Uand 8 Uinthesewaters were established using independent determination methods at IRMM and Bundesamt für Strahlenschutz (BfS). Various radiochemical methods were applied by the 45 laboratories participating in the comparison. The comparison results show that there are many discrepant measurement results for the radium isotopes; 19 results, corresponding to 14% of all, are off by a factor of two or more. For uranium, this proportion is much more favourable, with only 6% (9 results out of 15) off by a factor of two or more. As these samples had rather low activity concentrations around the detection limits required by the draft EC directive and not all laboratories are routinely analysing water for these radionuclides yet, unsatisfactory comparison results for 226 Ra and 2 Ra may not be unexpected. The comparison clearly demonstrates, however, that a number of monitoring laboratories need to improve their analysis procedures for radium in order to correctly identify the drinking water sources for which remedial action (with respect to their natural radioactivity concentration) needs to be taken. References Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit, 6. Messanleitungen für die Überwachung der Radioaktivität in der Umwelt und zur Erfassung radioaktiver Emissionen aus kerntechnischen Anlagen, Lieferungen 1 7, Stand 6. Chapter : Bestimmung von Uran, Plutonium und Americium mit extraktionschromatographischen Verfahren, H-U/Pu/Am- AWASS-1-1. Chapter 8: Verfahren zur Bestimmung von Radium-226 in Trinkwasser und Grundwasser, H-Ra-226-TWASS-1-1. Chapter 11: Verfahren zur Bestimmung der Aktivitätskonzentration von Radium-2 in Trinkwasser und Grundwasser, H-Ra-2-TWASS-1-1. Elsevier Urban & Fischer Verlag, München. ISBN and ISBN X. Burnett, W.C., Cable, P.H., Moser, R., Determination of radium-2 in natural waters using extraction chromatographic resins. Radioact. Radiochem. 6, 44. European Communities, Council Directive of 3 November 1998 on the quality of water intended for human consumption (98/83/EC). Official Journal L ( ) 54. European Communities, 1. Commission Recommendation of December 1 on the protection of the public against exposure to radon in drinking water supplies (1/9/Euratom). Official Journal L4 (..1) European Communities, 1. Council Directive, in preparation. ISO, 5. International Standard ISO 1:5(E), Statistical methods for use in proficiency testing by interlaboratory comparisons. International Standardization Organization, Geneva, Switzerland. Nour, S., El-Sharkawy, A., Burnett, W.C., Horwitz, E.P., 4. Radium-2 determination of natural waters via concentration on manganese dioxide and separation using Diphonix ion exchange resin. Appl. Radiat. Isot. 61, Pauwels, J., Lamberty, A., Schimmel, H., The determination of the uncertainty of reference materials certified by laboratory intercomparison. Accred. Qual. Assur. 3, Spasova, Y., Benedik, L., Vasile, M., Beyermann, M., Wätjen, U., Pommé, S., 9. 2 U and 8 U in mineral water: reference value and uncertainty evaluation in the frame of an interlaboratory comparison. J. Radioanal. Nucl. Chem. 1, 1 1. Spasova, Y., Wätjen, U., Benedik, L., Vasile, M., Altzitzoglou, T., Beyermann, M., 1. Evaluation of EC comparison for 226 Ra, 2 Ra, 2 U and 8 U in mineral waters. Report EUR xxxxx EN, ISBN xxxxx-x. Vasile, M., Altzitzoglou, T., Benedik, L., Spasova, Y., Wätjen, U., 9. Radiochemical separation and determination of 2 Ra in mineral waters by low-level liquid scintillation counting. In: Eikenberg, J., Jäggi, M., Beer, H., Baehrle, H. (Eds.), LSC 8, Advances in liquid scintillation spectrometry. Radiocarbon, Tucson, AZ, USA, pp Wätjen, U., Spasova, Y., Altzitzoglou, T., 8. Measurement comparisons of radioactivity among European monitoring laboratories for the environment and food stuff. Appl. Radiat. Isot. 66, WHO, Guidelines for drinking water quality, Recommendation, second ed. vol. 1. World Health Organization, Geneva, Switzerland. WHO, 6. Guidelines for drinking water quality, Recommendation, third (current) ed. including the first addendum, vol. 1. World Health Organization, Geneva, Switzerland. Benedik, L., Spasova, Y., Vasile, M., Wätjen, U., 8. Determination of 2 U, 8 U and 226 Ra in bottled drinking water by alpha spectrometry. In: CD Proceedings of the 7th International Conference on Nuclear and Radiochemistry (NRC-7), Budapest, Hungary, August 8. Benedik, L., Vasile, M., Spasova, Y., Wätjen, U., 9. Sequential determination of 21 Po and uranium radioisotopes in drinking water by alpha-particle spectrometry. Appl. Radiat. Isot. 67, Discussion: Q(Christian Hurtgen): In the intercomparison you have asked for people to give you a result for values that were above the EC

7 16 U. Wätjen et al. / Applied Radiation and Isotopes 68 (1) 1 16 detection limits, although some of them can measure lower than that. It is also a good idea to ask the laboratories to give results even if there is nothing, as it is a way to look at their blank. A(Uwe Wätjen): That is correct. We had discussed this, but - seen the short reaction time in which the laboratories had to report - we had decided not to ask for values much below the detection limits required by future legislation. Q(Guy Ratel): Do you have an action plan to resolve the problems that were hidden in the measurements? We can see that only a small number of laboratories could reach this level of quality. A(Uwe Wätjen): Together with EU member state representatives some action will certainly take place, because the European recommendations will have to be adopted by national legislation if they are not in place already. There are some countries that already have clear legislation that radium and uranium have to be measured. Concerning the analysis results, we discuss these values with participants of comparisons we had organized. In general, all of our comparisons are followed by a workshop for participants, sometimes combined for several comparisons. Q(Arvic Harms): When you measure Radium 2, you separate Actinium 2. How do you correct for your losses of actinium? Do you use yield rates for the actinium? If you go back to the separation scheme for Radium 2 I think you separate the Actinium 2 from the Radium 2 and you separate it by using a column. A(Uwe Wätjen): Yes, you are right, this has been calibrated. Mirela can you help with details? A(Mirela Vasile): We did a separate experiment using a natural thorium solution and we separated Actinium 2 which we measured with gamma-ray spectrometry using the 911 kev gamma line. We obtained for our separate experiment a 83% recovery which we then used in the activity calculation as a constant to correct for the actinium recovery from the second column. Q(Arvic Harms): So you did validate the method? A(Mirela Vasile): Yes, that s what we did. Q(Pierino de Felice): Are all the participants from European member states and did they pay a participation fee? A(Uwe Wätjen): No, this comparison is free of participation fees, but it is limited. Not everybody can participate; one needs a nomination by the national representatives. Q: 5% of laboratories with % uncertainty is not really a good result if you think that these laboratories will produce scientific results from let s say unknown samples and publish their results in their papers. So we have to take this into account. Do you have any follow up action plan as to how to improve the performance of these laboratories? A(Uwe Wätjen): The action plan for us consists in organizing discussions with the labs that participated, we cannot do much more. It is the responsibility of the lab to have its analysis procedures under control. With a demonstration of reference values and documentation of how these are established, they should at least know that they measured wrong and that the reference values are reliable. It is up to them to change the procedures or their implementation, we cannot oblige them to do so. We can only point it out to them and to their national representatives or authorities who nominated them to participate in the comparison. We hope that the national representatives are then also putting pressure on the laboratories to improve where necessary. Of course, in such a workshop there is opportunity to meet those people who participated in the comparison, and hopefully they will learn from each other.