Determination of Gross-Alpha & Gross-Beta Activity in Drinking Water via LSC

1. Determination of Gross-Alpha & Gross-Beta Activity in Drinking Water via LSC Sascha Wisser & Martina Koch ESWE-Institute for Water Research and Water Technology Wiesbaden, Germany

2. Contents • Introduction • Current Legislation within the E.U. • Basics of Freeze-Drying • Experimental Settings • Quality Assurance • Results & Discussion • Conclusion

3. The ESWE-Institute • Is a non-profit organization • Is funded by projects only • Has a budget of > 1,000,000 € / year • Is daughter of the municipal water supply company of Wiesbaden • Is connected to Mainz University • Is working in the field of Water Research and Water Technology

4. Department of Radioactivity • Determination of natural and artificial radionuclides in ground-, drinking- and mineral waters • Determination of radionuclides in solid matrices, such as residues from water treatment and filter materials • Radon-in-air measurements in waterworks • Consulting service for water supply companies, mineral water producers and breweries • Expert‘s reports in the field of natural radioactivity • Employees:Dr. Sascha Wisser • Dr. Dieter Fischer • Silvia Bleffert • Björn Kieser • + students

5. Current Legislation within the E.U. with respect to radioactivity in drinking water European Drinking Water Directive (1998) • Limiting value for 3H: 100 Bq/l • Total Ingestive Dose (TID): 0.1 mSv/a • Excluding 40K, 3H, 222Rn and Rn decay products The TID cannot be measured directly. Therefore, a troublesome and expensive determination of single radionuclides has to be performed ! Alternatively, the determination of so-called screening-parameters can be applied: Gross-Alpha / Gross-Beta Activity

6. Guidelines Values for Gross-Alpha/Beta Activity in Drinking Water (European Union) • If the Gross-Alpha Activity is < 0.1 Bq/l and the Gross-Beta Activity is < 1.0 Bq/l, it can be assumed that the TID is below 0.1 mSv/year. • Current research project, funded by the German Waterworks Association (DVGW), concluded that these Screening-Parameters are comparably reliable for a compliance with the TID • TID may be overestimated, since uranium is a major contributor to gross-alpha activity in drinking waters. Uranium has relatively low dose coefficients. However, the TID has never been underestimated during the project. • Gross-Beta activity is of minor importance for compliance with the TID

7. Why Apply Freeze-Drying to Determine Gross Alpha/Beta Activity ? • Sample preparation is simple and fast • Radon and its short-lived decay products are quickly stripped out of the water • Residue can be transferred to LSC-vial easily • Multiple samples can be treated at the same time at low lab-space demand • Troublesome evaporation-method can be avoided • Sample can be measured after a short standing time

8. Basics of Freeze-Drying Phase diagram of water with respect to temperature and water vapor pressure (after Oetjen & Haseley, 2003)

9. Freeze-Dryer at the ESWE-Laboratory • Up to 16 samples simultaneously • Vacuum: 1.0 x 10-3 bar • Freezing-temperature: - 22 °C • Water volume: max. 150 ml • Duration (16 samples): ~ 12 hours • Amount of residue: 25 – 1000 mg

10. Treatment of the Residue Scintillation Cocktail Transfer with a new plastic syringe (incl. new needle) Sample / Cocktail Mixture has to be transparent ! 0.5 N HCl (~ 4 ml) • Applicable LSC-Cocktails: • AquaLight • OptiPhase Hisafe 2

11. Alpha/Beta Separationwith Triathler Multilabel Tester Pulse- length Channel

12. Determination of the a-recovery („efficiency“) • Mixed 238U and 226Ra standard solution has been produced and subsequently freeze-dried • Target Values: from approx. 0.5 – 3.0 Bq/l

13. Determination of the b-recovery („efficiency“) • 40K standard solution has been produced and subsequently freeze-dried (made from pure KCl) • Target Values: from about 0.5 – 1.5 Bq/l

14. Limits of detection for gross-alpha activity with TriathlerTM Multilabel Tester • Background: 0,5 cpm • Recovery: 85 % (incl. counting efficiency) • Sample volume: 150 ml

15. Limits of detection for gross-beta activity with TriathlerTM Multilabel Tester • Background: 80 cpm (1,33 cps) • Recovery: 78 % (incl. counting efficiency) • Sample volume: 150 ml

16. Results of Intercomparisons Results are still satisfactory, since the sample waters were very different from drinking water quality. Conclusion: underestimation of the alpha-efficiency of TriathlerTM

17. Results of Control Samples Method is well established !! Measurement uncertainty: ± 15 %

18. Quality Assurance • Participation in interlaboratory comparison studies, organized by the German Radiation Protection Authority • Frequent measurements of control samples with known activity concentrations (at least monthly) • Application of Standard Operation Procedures for the entire method • Weekly determinations of background radiation (alpha and beta radiation) • Frequent testing of the used instrumentation, incl. alpha/beta separation and efficiency (~ weekly) • Complete documentation of the results of the quality measures and plotting in quality control cards Method has been accredited by the DACH (German Acceditation Service for Chemistry) in October 2003

19. Conclusions Final assessment: very good and reliable method for screening purposes in potable waters !!

20. Thank you very much for your attention ! Questions ??? Comments ??? Dr. Sascha Wisser Phone: + 49 611 2360 532 Email: sascha.wisser@eswe.com