Water quality. Actinium-227. Test method using alpha-spectrometry
Water quality. Actinium-227. Test method using alpha-spectrometry
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1 Scope This document specifies a test method to determine the activity concentration of 227 Ac in all types of waters by alpha spectrometry. The test method is applicable to test samples of supply/drinking water, rainwater, surface and ground water, marine water, as well as cooling water, industrial water, domestic, and industrial wastewater after proper sampling and handling and test sample preparation (see ISO 5667‑1, ISO 5667‑3, ISO 5667‑10). Filtration of the test sample is necessary. The detection limit depends on the sample volume, the instrument used, the background count rate, the detection efficiency, the counting time, the chemical yield, and the progeny ingrowth. The method described in this document, using currently available alpha spectrometry apparatus, has a detection limit of approximately 0,03 Bq·l −1 , when directly measuring the alpha peak of 227 Ac. This detection limit is lower than the WHO criteria for safe consumption of drinking water for any actinide alpha emitter (0,1 Bq·l −1 ). [ 4 ] This value can be achieved with a counting time of 48 h for a sample volume of 1 l. Only a small fraction of 227 Ac decays through alpha emissions (~1,42 %). An option to lower the detection limit of the method is to wait, let the progenies of 227 Ac grow in, and measure an alpha progeny peak of 227 Ac (e.g. 215 Po). This is a longer technique, but a lower detection limit of approximately 0,000 2 Bq·l −1 can be obtained by re-counting the sample approximately 90 days after purification. The sample can be re-counted before 90 days, but with a hi...
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