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The sources will improve atmospheric transport models which can be used to track both radon and greenhouse gases

The project

Radon is a naturally occurring radioactive gas that is emitted from all ice-free land. It is the leading source of public exposure to naturally occurring radioactive exposure and its activity concentration in the air is therefore monitored as part of radiation protection measures. European Council directive 2013/59/Euratom states the need to identify so-called “Radon Priority Areas” where specific protection measures need to be applied.

Due to its emanation and decay, radon is also an ideal tracer for assessing and improving the transfer models used to track atmospheric greenhouse gases. However, a lack of traceability for both radon flux (the rate of transfer of radon from ground to atmosphere per square metre of soil) and radon activity concentration (the amount of radon activity per cubic metre of atmosphere), as well as an inability to measure low levels of radon, has hampered its application.

EMPIR project ‘Radon metrology for use in climate change observation and radiation protection at the environmental level’ (19ENV01, traceRadon) has developed traceable measurements of low-level radon activity concentration as well as reference systems and transfer standards to extend capability for traceable radon flux measurements in the field. The project has also validated radon flux models and produced maps of radon and radon flux suitable for use in climate change and radiation protection research.

New radon sources

Following a literature review of the current state-of-the-art, project partners PTB, CMI and SÚJCHBO have developed several new principals for traceable radon emanation sources. Two examples are:

The first, developed by PTB, Germany’s National Metrology Network, has used a completely novel technological approach combining the source and the detector to one system called an Integrated Radon Source Detector (IRSD). In this IRSD, radium chloride (RaCl2), providing a tiny activity of radium, is layered directly onto the outside layer of a silicon semiconductor detector. This allows the IRSD to act as both emitter of radon and, through α-spectrum analysis, detector of radium, radon and decay products simultaneously. By this traceable emanation of radon activity is established.

The second, developed by CMI, the National Metrology Network of Czechia and SÚJCHBO, the National Institute for Nuclear, Chemical and Biological Protection of Czechia, is a ‘flow-through’ source using a higher activity source of radium bromide (RaBr2). This source was created directly from a primary source first developed in the 1950s and uses air to dilute the emanated radon to levels required for the reference atmosphere.

The new sources are able to produce radon activity concentrations below 20 Bq·m-3 to generate stable reference atmospheres and are suitable to be used as calibration standards in the field or in radon calibration chambers. First applications have showed that calibrations below 5 % uncertainty at these low activity concentrations are now feasible.

Other project achievements

• Radon emanation paper

The project has published a paper titled “Approximate sequential Bayesian filtering to estimate Rn-222 emanation from Ra-226 sources from spectra” in the Journal of Sensors and Sensor Systems, alongside an associated software package. The paper presents a novel method to estimate the activity concentration of radon emitted by a solid radium source. As this emanation is affected by factors such as humidity and temperature, previous methods were not suitable for field calibrations. The method presented in the paper overcomes this through continuous measurement and by accounting for dynamical processes within the source.

• New radon map service at the ICOS carbon portal

Project partner Lund University has implemented a new service on the Integrated Carbon Observation System (ICOS) carbon portal. The service provides daily and monthly European radon flux maps, on the same latitude-longitude grid as required by atmospheric transport models. The maps can be previewed on the portal or downloaded and visualised.

Project coordinator Annette Röttger (PTB) has said about the work of the project:

“When you define goals for a project, you never know whether you will be able to achieve them. Challenging goals, such as realizing the activity concentration of radon within the range of the low radon levels of the outside air, seemed an insurmountable hurdle. Until, with the right idea, everything suddenly became very simple. The IRSD was such an idea, and the reality has exceeded our expectations. I am very proud of the innovations that traceRadon has delivered, because they show that European metrology research can make measurable what was previously unmeasurable worldwide.”

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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