ISO/TC 147/SC 3/WG 16 - Alpha spectrometry

This document specifies a test method to determine the activity concentration of 227Ac 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 227Ac. 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 227Ac decays through alpha emissions (~1,42 %). An option to lower the detection limit of the method is to wait, let the progenies of 227Ac grow in, and measure an alpha progeny peak of 227Ac (e.g. 215Po). 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 higher detection limit. The test method(s) described in this document can be used during planned, existing and emergency exposure situations as well as for wastewaters and liquid effluents with specific modifications that can increase the overall uncertainty, detection limit and threshold. For an emergency situation, it is preferable to reduce the counting time rather than the sample volume. The analysis of 227Ac adsorbed to suspended matter is not covered by this document.

This document specifies the method and the conditions for the determination of 232Th activity concentration in samples of environmental water (including sea waters) and waste waters before release to the environment using alpha spectrometry and 229Th as a recovery tracer. A chemical separation allows to separate and purify thorium from a test portion of the sample. The general principles outlined in this document can be applied for the analysis of other alpha-emitting thorium isotopes such as 228Th and 230Th in aqueous samples.

This document specifies a test method for measuring actinides (238Pu, 239+240Pu, 241Am, 242Cm, 243+244Cm and 237Np) in water samples by alpha spectrometry following a chemical separation. This method can be used for any type of environmental study or monitoring after appropriate sampling and handling, and test sample preparation. The detection limit of the test method is 5 × 10−3 Bq·l-1 to 5 × 10−4 Bq·l-1 for a volume of test portion between 0,1 l to 5 l with a counting time of two to ten days. This is lower than the WHO criteria for safe consumption of drinking water (1 Bq·l-1 or 10 Bq·l-1 depending on radionuclide).[4] The method described in this document is applicable in the event of an emergency situation.