Knowledge of the precise life-time radon history in houses is essential for epidemiologists, mitigation professionals and house-owners. For radon dosimetry and to make a reasonable health-risk study similar information about the indoor aerosol environment is necessary. For this purpose a combined data analysis from measurements of the 210Po activity implanted in glass-surfaces as well as trapped in

spongy materials is proposed. This analysis technique provides a characterization of the average indoor 

aerosol-particle environment. As a consequence, a radon dose

estimation improves by a factor of about 3 compared to the commonly applied single surface-activity analysis

Oberstedt, S.

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IL NUOVO CIMENTO Maggio-Agosto 1999VOL. 22 C, N. 3-4Retrospective radon dosimetry (*)S. OBERSTEDTInstitute Laue-Langevin - 6 rue Jules Horowitz, F-38042 Grenoble Cedex 9, France(ricevuto il 9 Giugno 1998; approvato il 18 Novembre 1998)Summary. — Knowledge of the precise life-time radon history in houses is essentialfor epidemiologists, mitigation professionals and house-owners. For radon dosimetryand to make a reasonable health-risk study similar information about the indooraerosol environment is necessary. For this purpose a combined data analysis frommeasurements of the 210Po activity implanted in glass-surfaces as well as trapped inspongy materials is proposed. This analysis technique provides a characterization ofthe average indoor aerosol-particle environment. As a consequence, a radon doseestimation improves by a factor of about 3 compared to the commonly applied singlesurface-activity analysis.PACS 29.40 – Radiation detectors.PACS 92.60.Sz – Air quality and air pollution.PACS 01.30.Cc – Conference proceedings.1. – IntroductionThe strategies to assess the apparent health risk due to radon in the indoorenvironment rely principally on different types of information. In the first instance theactivity concentration of radon gas and of the short-lived radon daughters may bemeasured with the existing techniques rather precisely. On the contrary theassessment of dose relevant parameters, i.e. the fractional deposition of individualradon daughters across the respiratory tract, is difficult. Since these parameters arestrongly affected by the present aerosol-particle environment, the conclusions aretoday quite model dependent, and only a few experimental techniques exist, see, e.g.,ref. [1]. Anyway, all radon and radon-daughter measurements available act on amedium or even short term scale ranging from at best one year down to one day. Due tostrong daily and seasonal fluctuations in the indoor environment any evaluated riskfactor carries an uncertainty easily exceeding a factor of two. Therefore, retrospectiveassessment strategies on life-time scale have to be considered. Nowadays the analysis(*) Paper presented at the “Fourth International Conference on Rare Gas Geochemistry”,Rome, October 8-10, 1997.G Società Italiana di Fisica 341S. OBERSTEDT342of the 210Po activity implanted in glass surfaces (as ) is commonly used to obtaininformation on the integrated radon exposure [2]. Since deposition and implantation isstrongly affected by the present aerosol particles, the uncertainty on the radonexposure easily exceeds a factor of two [3, 4]. However, this degradation of the 210Posignal may be used as a measure for the aerosol-particle environment in the past. Therecently introduced analysis of the 210Po activity deposited in volume traps (av ), e.g.,spongy materials used for mattresses and cushions, provides a clear relationshipbetween the measured volume activity av and the radon exposure ERn , i.e. a veryaccurate information about the radon history [5] completely unaffected by the indoorair-quality. Therefore, a combination of both methods is compelling.With a combined surface1volume analysis it is possible to assess the radon historyas well as the dose-related parameters as the average value of the attachment rate (X),of the equilibrium factor (F) as well as of the unattached fraction of the short-livedradon progeny ( fu), retrospectively.2. – Description of the methodThe basic idea is the following. With the surface technique we obtain the surfaceactivity as and with the volume technique we measure the volume activity av , whichclearly relates to the exposure ERn4 cRn tex. Assuming an aerosol-free environment wecan calculate from av for a given surface-to-volume ratio S/V an equivalent surfaceactivity as , 0. The following relation between as , 0 and the measured as may then beconsidered:as4 F(X , l u , l a , l v , S/V ) as , 0 ,(1)with FE1, where l u , l a are the deposition velocities of the unattached and attachedradon decay-products, and l v denotes the ventilation rate.Next it is sufficient to assume l v and S/V as constants, which are characteristicvalues for the particular dwelling or even room being under investigation. Also, l u andl a are assumed to be log-normally distributed with ranges obtained from theFig. 1. – Comparison of the results obtained with the standard surface analysis and with thenew combined surface1 volume analysis. Left part: all possible combinations of the attachmentrate vs. radon exposure which reproduce a given as . Right part: distribution of the attachmentrate X.RETROSPECTIVE RADON DOSIMETRY 343literature [6, 7]. By entering cRn and X the dose-relevant parameters fu , fa and F for agiven surface activity as may be obtained using the room-model equations [6, 8, 9]. Thisis an iterative procedure for the attachment rate X. Starting with the single surfacetechnique it is clear from published experimental data [4, 10] that the measured surfaceactivity as may not clearly be correlated with a particular radon concentration, but cRnmust also be drawn randomly from a log-normal distribution. In consequence a largeuncertainty is added to the average attachment rate and so to the dose-relatedparameters. A simulation of a single surface-activity analysis has been performedassuming a surface activity as 4 10 Bq/m2 and an exposure period tex 4 10 y. Thedistributions for X(ERn ), F, fu and the annual dose Da based on 10000 entries arepresented in figs. 1 and 2.Introducing the volume-technique the simulation has been repeated entering amuch more precise value for cRn obtained from the measured volume activity av . In fact,cRn is now drawn randomly from a normal distribution with a standard deviationcorresponding to the experimental uncertainty of the volume-trap technique oftypically 10%. The mean value was chosen at 600 Bq/m3 according to the data fromref. [4]. The results for the same values of as and tex are shown together with theprevious results in figs. 1 and 2.Fig. 2. – Comparison of the results obtained with the standard surface analysis (broken line) andwith the new combined surface 1 volume analysis (full line). The upper row shows thedistribution of the equilibrium factor F and the lower row gives the corresponding distributions ofthe average annual dose Da. Left part: tex 4 10 y, as 4 10 Bq/m2, ERn 4 6 kBq/m3 y; right part:tex 4 20 y, as 4 5 Bq/m2, ERn 4 6 kBq/m3 y.S. OBERSTEDT344The corresponding annual dose Da has been calculated according toDa ( mSv/y )40.81 mSv/y6 Bq/m3 NEECF cRn ,(2)with a conversion factor estimated from refs. [11, 12]. The factor 0.8 takes into accountthe residential probability at home.As is obvious from both figures, the distributions for F and X obtained with thecombined surface1volume analysis are much narrower. The relative uncertainty for Daobtained from the surface analysis is 44% and from the combined analysis only 12%. Asimilar result has been obtained for as 4 5 Bq/m2 and a similar exposure scenario,tex 4 20 y and cRn4 300 Bq/m3. Here, the corresponding uncertainties were 45% and 14%.3. – ConclusionFor both surface activities evaluated, 5 Bq/m2 and 10 Bq/m2, the combined sur-face1volume analysis shows up an annual dose estimation being roughly a factor of 3more precise than the usually applied surface technique. This is clearly due to theprecise knowledge of the average radon concentration provided by the volumetechnique. In conclusion a combined sampling of glass material and volume-trapmaterial during forthcoming epidemiologies is highly recommended.R E F E R E N C E S[1] OBERSTEDT S. and VANMARCKE H., The Bronchial Dosemeter, Rad. Prot. Dosim., 59 (1995)285-290.[2] LIVELY R. S. and NEY E. P., Surface radioactivity resulting from the deposition of 222Rndaughter products, Health Phys., 52 (1987) 411-415.[3] CORNELIS J., LANDSHEERE C., VAN TRIER A., VANMARCKE H. and POFFIJN A., Experimentson glass-absorbed polonium-210, Appl. Rad. Isot., 43 (1992) 127-138.[4] SAMUELSSON C., JOHANSSON L. and WOLFF M., 210Po as a tracer for radon in dwellings, Rad.Prot. Dosim., 45 (1992) 73-75.[5] OBERSTEDT S. and VANMARCKE H., Volume traps—a new retrospective radon monitor,Health Phys., 70 (1996) 222-226.[6] PORSTENDÖRFER J., Properties and Behaviour of Radon and Thoron and their DecayProducts, CEC-Report EUR 14411EN (1993) p. 116 ff.[7] ALDENKAMP F. J. and STOOP P., Sources and Transport of Indoor Radon — Measurementsand Mechanisms, Doctoral Thesis, University of Groningen (1994).[8] JACOBI W., Activity and Potential Alpha-Energy of Rn-222- and Rn-220 Daughters inDifferent Air Atmospheres, Health Phys., 22 (1972) 441-450.[9] VANMARCKE H., BERKVEN P., POFFIJN A. and RAES F., Uncertainties in Radon DaughterMeasurement arising from Fluctuations in Room Parameters, Rad. Prot. Dosim., 24 (1988)225-230.[10] SAMUELSSON C. and JOHANSSON L., Long-lived Radon Decay Products as a Long-termRadon Exposure Indicator, Rad. Prot. Dosim., 56 (1994) 123-126.[11] PHILIPSBORN H., Strahlenschutz, Radioaktivität und Strahlungsmessung, Herausgeber:Bayrisches Staatsministerium für Landesentwicklung und Umweltfragen, ISBN3-910088-01-5, 2. Auflage (1994) p. 162.[12] ICRP, Protection against radon-222 at home and at work, ICRP-publication 65, Ann. ICRP,23 (1993).

Retrospective radon dosimetry

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Retrospective radon dosimetry

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