ISO/TC 147/SC 3/WG 15 - Liquid scintillation counting and proportional counting

This document describes a test method for the determination of radon-222 (222Rn) activity concentration in non-saline waters by extraction and liquid scintillation counting. The 222Rn activity concentrations, which can be measured by this test method utilizing currently available instruments, are above 0,5 Bq·l−1 which is the typical detection limit for a 10 ml test sample and a measuring time of 1 h. It is the responsibility of the laboratory to ensure the validity of this test method for water samples of untested matrices. Annex A gives indication on the necessary counting conditions to meet the required detection limits for drinking water monitoring.

This document specifies the determination of radium-226 (226Ra) activity concentration in non-saline water samples by extraction of its daughter radon-222 (222Rn) and its measurement using liquid scintillation analysis. The test method described in this document, using currently available scintillation counters, has a detection limit of approximately 50 mBq·l−1. This method is not applicable to the measurement of other radium isotopes.

This document specifies the determination of nickel-59 and nickel-63 (59Ni and 63Ni) activity concentration in samples of all types of water using liquid scintillation counting (LSC). Using currently available liquid scintillation counters, this test method can measure 59Ni activity concentrations of 50 mBq·l−1 and 63Ni activity concentrations of 20 mBq·l−1 with a counting time of 200 min and a sample volume of 1,5 l. NOTE These performance indicators are wholly dependent on the measurement regimes in individual laboratories; in particular, the detection limits for 59Ni are entirely dependent on the levels of 63Ni that can be present. The range of application depends on the amount of dissolved material in the water and on the performance characteristics of the measurement equipment (background count rate and detection efficiency). It is the laboratory’s responsibility to ensure the suitability of this test method for the water samples tested.

This document specifies conditions for the determination of 90Sr and 89Sr activity concentration in samples of environmental water using liquid scintillation counting (LSC) or proportional counting (PC). The method is applicable to test samples of 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. Filtration of the test sample and a chemical separation are required to separate and purify strontium from a test portion of the sample. The detection limit depends on the sample volume, the instrument used, the sample count time, the background count rate, the detection efficiency and the chemical yield. The method described in this document, using currently available LSC counters, has a detection limit of approximately 10 mBq l−1 and 2 mBq l−1 for 89Sr and 90Sr, respectively, which is lower than the WHO criteria for safe consumption of drinking water (100 Bq·l−1 for 89Sr and 10 Bq·l−1 for 90Sr)[3]. These values can be achieved with a counting time of 1 000 min for a sample volume of 2 l. The methods described in this document are applicable in the event of an emergency situation. When fallout occurs following a nuclear accident, the contribution of 89Sr to the total amount of radioactive strontium is not negligible. This document provides test methods to determine the activity concentration of 90Sr in presence of 89Sr. The analysis of 90Sr and 89Sr adsorbed to suspended matter is not covered by this method. It is the user’s responsibility to ensure the validity of this test method selected for the water samples tested.

This document specifies a method for the measurement of 210Pb in all types of waters by liquid scintillation counting (LSC). The method is applicable to test samples of supply/drinking water, rainwater, surface and ground water, as well as cooling water, industrial water, domestic, and industrial wastewater after proper sampling and handling, and test sample preparation. Filtration of the test sample is necessary. Lead‑210 activity concentration in the environment can vary and usually ranges from 2 mBq l-1 to 300 mBq l-1 [27][28]. Using currently available liquid scintillation counters, the limit of detection of this method for 210Pb is generally of the order of 20 mBq l-1 to 50 mBq l-1, which is lower than the WHO criteria for safe consumption of drinking water (100 mBq l−1).[4][6] These values can be achieved with a counting time between 180 min and 720 min for a sample volume from 0,5 l to 1,5 l. Higher activity concentrations can be measured by either diluting the sample or using smaller sample aliquots or both. The method presented in this document is not intended for the determination of an ultra-trace amount of 210Pb. The range of application depends on the amount of dissolved material in the water and on the performance characteristics of the measurement equipment (background count rate and counting efficiency). The method described in this document is applicable to an emergency situation. The analysis of Pb adsorbed to suspended matter is not covered by this method. It is the user’s responsibility to ensure the validity of this test method for the water samples tested.

This document specifies a method for the measurement of 14C activity concentration in all types of water samples by liquid scintillation counting (LSC) either directly on the test sample or following a chemical separation. 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. The detection limit depends on the sample volume, the instrument used, the sample counting time, the background count rate, the detection efficiency and the chemical recovery. The method described in this document, using currently available liquid scintillation counters and suitable technical conditions, has a detection limit as low as 1 Bq∙l−1, which is lower than the WHO criteria for safe consumption of drinking water (100 Bq·l-1). 14C activity concentrations can be measured up to 106 Bq∙l-1 without any sample dilution. It is the user’s responsibility to ensure the validity of this test method for the water samples tested.

This document specifies a test method for the determination of iron-55 (55Fe) activity concentration in samples of all types of water using liquid scintillation counting (LSC). Using currently available liquid scintillation counters, this test method can measure the 55Fe activity concentrations in the range from the limit of detection up to 120 mBq l-1. These values can be achieved with a counting time between 7 200 s and 10 800 s for a sample volume from 0,5 l to 1,5 l. Higher activity concentrations can be measured by either diluting the sample or using smaller sample aliquots or both. NOTE These performance indicators are wholly dependent on the measurement regimes in individual laboratories; in particular, the detection limits are influenced by amount of stable iron present. The range of application depends on the amount of dissolved material in the water and on the performance characteristics of the measurement equipment (background count rate and counting efficiency). It is the laboratory’s responsibility to ensure the suitability of this test method for the water samples tested.

ISO 13168:2015 describes a test method for the simultaneous measurement of tritium and carbon-14 in water samples by liquid scintillation counting of a source obtained by mixing the water sample with a hydrophilic scintillation cocktail. This is considered a screening method because of the potential presence of interfering nuclides in the test sample. The method can be used for any type of environmental study or monitoring. ISO 13168:2015 is applicable to all types of waters having an activity concentration ranging from 5 Bq/l to 106 Bq/l (upper limit of the liquid scintillation counters for direct counting). For higher activity concentrations, the sample can be diluted to obtain a test sample within this range.