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Radon progeny is not so noble
Posted on Feb 7, 2018 by Safe Radiation
Radon-222 is an isotope of the noble gas ‘radon’. It is radium-226’s daughter. Its genealogy can be traced upwards as the seventh generation of a primordial series parent uranium-238. Variable quantities of uranium and its entire generations of progeny can be found in different rocks and minerals. Being a gas, some of radon exhales from the rocks and appears as traces in the air.
Radon-222 inhalation is associated with increased probability of lung cancer. However, in fact, the radiation dose dominantly comes upon the inhalation of its short lived progeny which remains air-borne as radon disintegrates. Following the radon-222 progeny inhalation and upon its deposition in the lung, alpha emissions due to polonium-218 and polonium-214 disintegration deliver most radiation dose.
Areas of elevated uranium concentration in the rocks, mineral processing plants, and labs or storage places with uranium minerals and chemicals, or 226Ra sources are likely to have radon-222 concentration at above ambient levels. Also radon will build-up in poorly ventilated areas.
Radon and lung cancer association has been subject to several international investigations. In 2010, the International Commission on Radiological Protection (ICRP) reviewed its approach about calculating the radon progeny inhalation dose. (Lung Cancer Risk from Radon and Progeny and Statement on Radon. ICRP Publication 115, Annals of the ICRP Volume 40 (1). An abstract of this publication can may be seen at: http://www.icrp.org/publication.asp?id=ICRP%20Publication%20115.
Yesterday 5 February 2018, the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) released an advisory note titled ‘New Dose Coefficients for radon progeny: impact on workers and public’.
The report mentions that, ‘Applying the new ICRP dose coefficients, the estimates of average radiation dose from exposure to radon in Australian homes would increase by a factor of more than two, from 0.2 mSv per year to 0.5 mSv per year.’ Similar increases in dose estimates are expected in other areas where radon concentration is generally elevated – such as uranium mines and underground recreational caves.
The average radon concentration in the Australian homes is low compared to the international average. In 2000, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) prepared a report for the General Assembly. Table 24 of the Scientific Annex B of this report provides a summary of worldwide measurements of radon in dwellings. The reported Australian average is 11 Bq in a cubic metre of air, while the corresponding global population weighted average is 39 Bq.
ARPANSA recommended radon-222 concentration reference levels for considering action were given in Radiation Protection Series 1, Republished March 2002, Annex C, page r-39.
They have been reviewed in a 2017 guideline but unchanged (Guide for Radiation Protection in Existing Exposure Situations). The reference levels are 200 Bq per cubic metre of air in dwellings and 1000 Bq per cubic metre at workplaces.
Over the years, Safe Radiation has contributed to ensure workplace and environmental radiation safety through radon exhalation and atmospheric concentration measurements at mine sites, potentially contaminated lands, less ventilated areas, laboratories, and radioactive material stores. Engage us to see Safe Radiation difference.