Speaker
Description
Rn-220 (thoron) can be found in indoor spaces in different concentrations when Th-232 is contained in the building materials. Because of its effects on human health, according to the Council directive 2013/59/EURATOM, thoron must be taken into consideration when determining the corresponding occupational and public exposure.
Nonetheless, thoron is often neglected in radiation assessment as compared to its sister Rn 222 (radon): because of its short half-life time (55.6 seconds) it cannot diffuse further than a few tens of centimetres away from the walls and the spatial distribution of the indoor concentration is strongly inhomogeneous. For this reason, it is difficult to consider the measurand “thoron activity concentration” as representative for the risk connected to a specific indoor space.
On the other side, thoron progeny has significantly longer half-life times and can diffuse in the indoor space in a more homogeneous way. Furthermore, the biggest contribution to the dose of thoron is given by the inhalation of its progeny, so it is more representative as well as accurate to measure directly the thoron progeny through the potential alpha energy concentration (PAEC).
To understand if and how much thoron and its progeny are of concern or not, it is necessary to perform metrologically traceable measurements with quality assured methods, but a metrological structure for these measurements is currently not available in Europe. Addressing this gap, the Radon Metrology department (UR1) of BfS initiated the design of a chamber to create standard atmospheres for thoron decay products with the aim of performing instrument calibrations for the measurand PAEC. The current status of the development of the chamber as well as difficulties and open questions regarding thoron progeny calibrations will be discussed.