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EMPIR project contributes to new patents for more accurate radon sensors

EMPIR project setup of radon detectors with a temperature compensating design, enabling radon measurement that is reactive to in-the-moment temperature changes © University of Sofia

Work by an EMPIR project has contributed to two new national patents for regulators to improve the performance of radon sensors

Completed EMPIR project Metrology for radon monitoring (16ENV10, MetroRADON) has developed methods to monitor and reduce public exposure to radon.

Radon (222Rn) is a radioactive element which occurs naturally in the environment, with some areas experiencing higher levels than others due to local geological processes. Despite a short half-life, radon can also accumulate inside buildings. Radon exposure is thought to be responsible for 15 000 to 20 000 annual deaths due to lung cancer throughout Europe, making radon monitoring both inside and outside a key public health concern. To help meet the EU Basic Safety Standards (EU-BSS) maximum limit for radon activity concentration inside workplaces – set at 300 Bq/m3 – the MetroRADON project developed measurement techniques and reference materials to calibrate radon measurement instruments. These include novel techniques such as using CD/DVD discs to quantify radon activity and methods to reduce bias in radon measurements caused by the isotope thoron (220Rn).

New patents

Project partner Sofia University, located in Sofia, Bulgaria, has registered two national patents incorporating work from the MetroRADON project.

The patents both describe compensatory sensor modules, which correct the influence of temperature on measurements of 222Rn in gasses and liquids. Changes in temperature can have a profound effect on measurements for radioactive noble gases, as they alter the calibration factor required to convert between the signal measured by the sensor and the equivalent concentration. Many sensors are based on activated charcoal, for which an increase in temperature of ~20°C can cause a twofold decrease in the calibration factor, leading to lower concentrations being recorded.

Methods to shield from temperature changes altogether, such as closing the sensor inside a hermetically sealed package, have been used in the past. However, these packages are usually made from materials such as low-density polyethylene and trap a large amount of air inside, causing the sensor to become bulky, with a new level of care being required to protect the surrounding package. This is unsuitable for sensors installed in domestic or workplace settings, where space may be limited, and also makes it impossible to adapt the sensors to create hand-held versions or incorporate them into existing devices.

The first patent registered by Sofia University (Reg. No. 67405 B1) describes a new design of temperature compensator for use with radon sensors. This uses a polymer film to regulate the rate at which gas reaches the sensor. The film becomes more permeable as the temperature increases, causing more gas to pass through and compensating for the reduction in the calibration factor. However, this design is still unsuitable for some applications due to its size and shape. The second patent (Reg. No. 67484 B1) therefore improves upon the first, describing design of compensator which utilises a tight-fitting hermetically sealed package following the shape of the sensor inside. The result is a much smaller and thinner sensor unit.

The development of these temperature compensators allows for an approach to radon measurement that is reactive to in-the-moment temperature changes and has the additional benefit of being small enough to be used in a wider range of applications.

Project coordinator Franz Josef Maringer (BEV) has said on the work of the project:

“The newly patented design for compensating the temperature dependence of radon detectors, which were developed in the MetroRADON project, represent a very valuable method for improving the reliability and accuracy of radon measurements in Europe and 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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