Onderzoek naar de radioactiviteit van oppervlaktewater. Resultaten over 1990

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this report contains the results for 1990 of measurements of radioactivity in the rivers Meuse, Rhine, Roer, in the Westerscheldt, in the Channel of Sas van Gent to Terneuzen, and in het North Sea along the Dutch coast. The Sr-90-content in Meuse, Rhine and Roer varies between 2.4 Bq/m3 and 6.9 Bq/m3. In the Westerscheldt higher contents are found (between 9 Bq/m3 and 22 Bq/m3. The Sr-90-content of seawater varies between 7 Bq/m3 and 12 Bq/m3. Sr-89 was not found. As in previous ywars, the Ra-226- contents found in samples of the Roer (between 11 Bq/m3 and 14 Bq/m3) are higher than the ones measured in samples of the Meuse and of the Rhine (between 2.0 Bq/m3 and 6.1 Bq/m3). The Ra-226-content of the Westerscheldt varies between 6 Bq/m3 and 38 Bq/m3. The Po-210 and Pb-210-contents of the Meuse, Rhine and Roer are almost the same. The Po-210 and Pb-210-contents of the Westerscheldt are considerably higher than the contents of the rivers mentioned above: the yearly average of the Po-210-content is 26.3 Bq/m3 and of the Pb-210-content 24.2 Bq/m3. The Po-210 and Pb-210-contents of the Westerscheldt have increased during the last four years. Samples of suspended matter from the Meuse, Rhine, Roer, Westerscheldt and the Channel of Sas van Gent to Terneuzen were examined by means of gammaspectrometry. Natural as well as artificial radionuclides are found. The H-3-contents in the North Sea (between 1100 Bq/m3 and 3500 Bq/m3) are generally the same as in 1989. The Cs-137-contents measured vary between less than the detection limit (2 Bq/m3) and 25 Bq/m3.