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The Importance of Nanosize Aerosols of Radon Decay Products in Radon Dosimetry

Croatian Chemical Society
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vaupotic.vp The Importance of Nanosize Aerosols of Radon Decay Products in Radon Dosimetry* Janja Vaupoti~ and Ivan Kobal** Jo`ef Stefan Institute, 1000 Ljubljana, Slovenia RECEIVED DECEMBER 6, 2006; REVISED MARCH 14, 2007; ACCEPTED MARCH 16, 2007 Air concentrations of radon and radon short-lived decay products, equilibrium factor, unattach- ed fraction of radon decay products (fun), barometric pressure, air temperature and relative air humidity in the Postojna Cave and in a kindergarten were measured, with the emphasis on fun. Applying the dosimetry model, dose conversion factors were calculated on the basis of fun values obtained (ranging from 0.09 to 0.65 in the cave and from 0.03 to 0.25 in the kindergarten) and shown to exceed significantly 5 mSv WLM–1, the value proposed on the basis of epidemiolo- gical studies. Keywords radon radon short-lived decay products unattached fraction air karst cave kindergarten CROATICA CHEMICA ACTA CCACAA 80 (3-4) 565¿573 (2007) ISSN-0011-1643 CCA-3200 Original Scientific Paper INTRODUCTION Radon is a radioactive noble gas formed by radioactive decay of radium in natural radioactive decay chains in the Earth’s crust, i.e., 222Rn isotope (a decay, half-life, t1/2 = 3.82 days) from 226Ra in the 238U chain, 220Rn iso- tope (a decay, t1/2 = 55 s) from 224Ra in the 232Th chain, and 219Rn isotope (a decay, t1/2 = 3.92 s) from 223Ra in the 235U chain.1 Only a small fraction of radon (described as the emanation coefficient) enters the space between mineral grains and, thus, has the possibility to travel away from the source, carried either by carrier gases (methane, carbon dioxide) or by water.2 It accumulates in underground rooms (karst caves, mines) and eventual- ly reaches the living and working environment. Of the three radon isotopes, only 222Rn (also simply called ra- don) is usually of concern to humans, since it appears at a considerable level in the atmosphere because of its long half-life compared with half-lives of 220Rn (tho

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