Measurement of radium concentration in water | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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Physics of natural sites

  Measurement of radium concentration in water

Measurement of radium-226 in water

Since 2009, two methods are experimented to measure radium-226 concentration activity in water: a standard method, in which the concentration is obtained a few hours after air sampling, and one high-sensitivity method that requires a counting session of 24 hours at least, and a preparation of at least 3 days to measure precisely the background count in every instance. In both methods, the measurement by radon emanometry requires a prior accumulation time of the container, with the liquid to be measured, of duration larger than one month, more if the initial radon-222 concentration is high. More than 820 measurements of radium-226 in water have been performed before April 2017.

Instruments

Scintillating flasks and CALENTM photomultiplier counters.

 

Experimental protocol

Water (or the other liquid to measure) must be transferred in a glass container (bottles, Erlenmeyer flasks, flat bottom flasks), leaving a certain quantity of air in the container before closing it with a pre-perforated stopper. For water from a natural spring, 800 mL of water in a 1 L container is sufficient. When the radium-226 concentration is small (of the order of 50 mBq/L or smaller, which is frequent for natural surface waters), it is better to use 1800 mL of water in a 2 L container. The container must then be stored for a sufficiently long time so that all initially present radon-222 will disintegrate, at least one month, and sometimes longer than three months if the initial radon-222 concentration is larger than 500 Bq/L, which is frequently the case in granitic areas and for some geothermal systems. After this equilibration time, the remaining radon-222 in the container is in radioactive equilibrium with the radium-226 contained in the liquid.

The measurement consists, as in the case of radon-222, in establishing chemical equilibrium between the air and the liquid phase by shaking, followed by sampling of the air using a scintillating flask. In the case of radium-226, by contrast with radon-222 comparatively easy to measure, it is often necessary to use the high-sensitivity method. Generally, the container is mildly heated (40 °C) to improve the detection limit.

Details of the methods, systematic effects and validation tests are described in Girault & Perrier (2014) for the standard method and in Perrier et al. (2016) for the high-sensitivity method (see references below).

 

Experimental uncertainties

Typical uncertainties for the standard method (S) and the high-sensitivity method (L) are given in the graph below, separating measurements with container of volume <1 L, from those of volume  >2 L, with and without heating.

Applications

Given the fact that radium-226 concentrations are generally small and need to be measured with care, these two methods are generally used in the laboratory. However, they can also be applied in the field when the conditions are adequate, even in remote areas without electricity. The methods have mostly been applied so far for radium concentration in water, but the methods apply to any liquid in principle, provided the partition coefficient of radon between air and the given liquid is known as a function of temperature. Tests have been performed with sodas, coke, wine, etc...

 

Contact

Measurements can be carried out on demand. To get a price offer, please get in touch with one team member (perrier@ipgp.fr or girault@ipgp.fr), stating the goals and conditions.

 

Manufacturer of the instruments

www.algade.fr

 

Documents

General introduction on radium-226 concentration in water: Girault, F., F. Perrier, T.A. Przylibski, Radon-222 and radium-226 occurrence in water: A review, In Gillmore, G.K., Perrier, F.E., Crockett, R.G.M. (eds) Radon, Health and Natural Hazards. Geological Society, London, Special Publications, 451, SPA451.3, 2016.

Validations and examples of results: case of the Himalayas of Nepal:

Girault, F., B.P. Koirala, M. Bhattarai, F. Perrier, Radon and carbon dioxide around remote Himalayan thermal springs, In Gillmore, G.K., Perrier, F.E., Crockett, R.G.M. (eds) Radon, Health and Natural Hazards. Geological Society, London, Special Publications, 451, SPA451.6, 2016.

Girault, F., F. Perrier, The Syabru-Bensi hydrothermal system in central Nepal: 2. Modeling and significance of the radon signature, Journal of Geophysical Research Solid Earth, 119, 4056-4089, 2014.

High-sensitivity method, tests and applications:

Perrier, F., J. Aupiais, F. Girault, T.A. Przylibski, H. Bouquerel, Optimized measurement of radium-226 concentration in liquid samples with radon-222 emanation, Journal of Environmental Radioactivity, 157, 52-59, 2016.