Significant reduction in indoor radon in newly built houses.

Results from two national surveys of radon in newly built homes in Norway, performed in 2008 and 2016, were used in this study to investigate the effect of the 2010 building regulations introducing limit values on radon and requirements for radon prevention measures upon construction of new buildings. In both surveys, homes were randomly selected from the National Building Registry. The overall result was a considerable reduction of radon concentrations after the implementation of new regulations, but the results varied between the different dwelling categories. A statistically significant reduction was found for detached houses where the average radon concentration was almost halved from 76 to 40 Bq/m3. The fraction of detached houses which had at least one frequently occupied room with a radon concentration above the Action Level (100 Bq/m3) fell from 23.9% to 6.4%, while the fraction above the Upper Limit Value (200 Bq/m3) was reduced from 7.6% to 2.5%. In 2008 the average radon concentration measured in terraced and semi-detached houses was 44 and in 2016 it was 29 Bq/m3, but the reduction was not statistically significant. For multifamily houses, it was not possible to draw a conclusion due to insufficient number of measurements.

Outdoor thoron and progeny in a thorium rich area with old decommissioned mines and waste rock.

Radon (222Rn), thoron (220Rn) and their decay products may reach high levels in areas of high natural background radiation, with increased risk associated with mining areas. Historically, the focus has mostly been placed upon radon and progeny (RnP), but recently there have been reports of significant contributions to dose from thoron progeny (TnP). However, few direct measurements of TnP exist under outdoor conditions. Therefore, we assessed the outdoor activity concentrations of radon, thoron and TnP in an area of igneous bedrock with extreme levels of radionuclides in the thorium decay series. The area is characterized by decommissioned mines and waste rock deposits, which provide a large surface area for radon and thoron emanation and high porosity enhancing exhalation. Extreme levels of thorium and thoron have previously been reported from this area and to improve dose rate estimates we also measured TnP using filter sampling and time-integrating alpha track detectors. We found high to extreme levels of thoron and TnP and the associated dose rates relevant for inhalation were up to 8 µSvh-1 at 100 cm height. Taking gamma irradiation and RnP into account, significant combined doses may result from occupancies in this area. This applies to recreational use of the area and especially previous and planned road-works, which in the worst case could involve doses as large as 23.4 mSv y-1. However, radon and thoron levels were much more intense on a hot September day than during time-integrated measurements made the subsequent colder and wetter month, especially along the ground. This may be explained by cold air observed flowing out from inside the mines through a drainage pipe adjacent to the measurement stations. During warm periods, activity concentrations may therefore be due to both local exhalation from the ground and air ventilating from the mines. However, a substantially lower level of TnP was measured on the September day using filter sampling, as compared to what was measured with time-integrative alpha track detectors. A possible explanation could be reduced filter efficiency related to the attached progeny of some aerosol sizes, but a more likely cause is an upwards bias on TnP detectors associated with assumed deposition velocity, which may be different in outdoor conditions with wind or a larger fraction of unattached progeny. There is thus a need for better instrumentation when dealing with outdoor TnP.