Standards Development

Scope

This standard specifies a method for the measurement of 227Ac in all types of waters by alpha spectrometry.

The 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. A 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 chemical yield, and the daughter ingrowth. The method described in this standard, using currently available alpha spectrometry apparatus, has a detection limit of approximately 30 mBq·l-1 (or mBq·kg-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 alpha emitter (100 mBq·l-1). This value can be achieved with a counting time of 48 hours for a sample volume of 1l.

A lower detection limit can be obtained using the same method by letting the daughters of 227Ac grow, and measure a daughter peak of 227Ac (e.g. 215Po) later. This is a longer technique, but a lower detection limit of approximately 0.2 mBq·l-1 can be obtained by re-counting the sample 90 days after purification. The sample can be re-counted before 90 days, but the detection limit will be higher.

The method described in this standard is applicable in the event of an emergency situation.

The analysis of 227Ac adsorbed to suspended matter is not covered by this method.

Purpose

Purpose and justification of the proposal

Natural radionuclides, such as 227Ac, including those originating from the thorium and uranium decay series, can be found in water for natural reasons such as desorption from the soil and washoff by rain water or can be released from technological processes involving naturally occurring radioactive materials such as mining and processing of mineral sands or phosphate fertilizers production and use.

227Ac is also made artificially by the radio-pharmaceutical industry for the production of the medical isotope 223Ra used in advanced prostate cancers. 227Ac is a very radiotoxic isotope because it decays to several short-live alpha emitters. Drinking-water may contain 227Ac at activity concentrations which could present a risk to human health. In order to assess the quality of drinking-water, including mineral waters and spring waters, 227Ac radioactivity content has to be monitored as recommended by the World Health Organization [WHO] and might be required by some national authorities.

A standard on 227Ac determination in water samples is of interest for:

- The radio-pharmaceutical industry (223Ra production);

- The uranium mining industry;

- The rare-earth mining and purification industry;

- The uranium fuel fabrication industry;

- Geological and oceanographic studies. 

Only a few methods to measure 227Ac in water samples have been published and no standardized methods to determine 227Ac in drinking water exists. The need for a standard method on 227Ac measurement in water samples is justified for testing laboratories carrying out radioactivity measurements, may be required for the radioactivity monitoring of drinking water by national authorities, as they might need to get a specific accreditation for 227Ac measurement.

Consider the following:

Is there a verified market need for the proposal?

What problem does this document solve?

What value will the document bring to end-users?

See Annex C of the ISO/IEC Directives part 1 for more information.

See the following guidance on justification statements in the brochure ‘Guidance on New work’: https: //www.iso.org/publication/PUB100438.html