Exposure radon daughters

Many states in the U.S. are currently involved in large scale surveys to measure radon levels in homes in an attempt to assess the environmental risk from radon and radon daughter exposure. Radon daughters deliver the largest radiation exposure to the population and it is estimated that 0.01% of the U.S. population (23,000 persons) are exposed from natural sources to greater than those levels allowed occupationally (4 WLM/yr) (NCRP, 1984). 

Working level (WL) The allowable level ot exposure of a person to an atmosphere that contains any combination of Radon daughters. 

Working level month (WLM) An exposure ot I WLM can be taken to be received by a person working in a Radon daughter concentration of 1 WL for 170 hours. 

Working Level Month (WLM)—A unit of exposure to radon daughters corresponding to the product of the radon daughter concentration in Working Level (WL) and the exposure time in nominal months (1 nominal month =170 hours). Inhalation of air with a concentration of 1 WL of radon daughters for 170 working hours results in an exposure of 1 WLM. 

Jacobi, W. and Paretzke H.G. 1985, Risk Assessment for Indoor Exposure to Radon Daughters, In Proceedings, Seminar on Exposure to Enhanced Natural RAdiation and Its Regulatory Implications, Maastricht, the Netherlands, March 25-27, Elsvier Science Publisher, Amsterdam. 

Lundin R.E., Wagoner J.K. and Archer V.E., 1971, Radon Daughter Exposure and REspiratory Cancer-Quantitive and Temporal Aspects,... 

Relation Between Long-Term Exposure to Radon Daughters, Proceed,... 

Sevc J., Kunz E. and Placek V., 1976, Lung Cancer in Uranium Miners and Long-Term Exposure to Radon Daughter Products, Health Phys.,... 

Swedjemark, G.A. and MjOnes, L. Exposure of the Swedish population to radon daughters, in Proceedings of the 3rd International Conference on Indoor Air Quality and Climate, Stockholm, 1984, 2, pp. 37-43, Swedish Council for Building Research, Stockholm (1984). 

Swedjemark, G.A., Radon and its decay products in housing - estimation of the radon daughter exposure to the Swedish population and methods for evaluation of the uncertainties in annual averages, Thesis, Department of Radiation Physics, University of Stockholm (1985). 

Castren, 0., The contribution of bored wells to respiratory radon daughter exposure in Finland. Proc. of Symposium on Natural Radiation Environment, (C0NF- 780422, vol.2.) pp. 1364-1370, Houston, Texas (1978). 

In the radon surveys the primary quantity determined is the indoor air mean radon activity concentration. From a radiological health perspective it is the dose arising from the inhalation of radon daughters that is of interest. The conversion from radon exposure to annualised effective dose equivalent for the survey was carried out using the factors given in Table I which are similar to those being used in other European surveys. The occupancy and equilibrium factors given in this table are assumed mean values for Irish... 

Some of the 220 detectors recently recovered have been analysed not only for radon exposure but also to determine the value of F (the equilibrium factor) in the houses. A preliminary set of such F factor results, obtained by analysing the inner and outer LR- 115 track densities of each detector, are presented in Table III for 12 houses with mean indoor radon concentrations greater than 200 Bq/nP. In Table III are also presented radon daughter doses estimated using the individually determined equilibrium factor values F together with the doses estimated on the basis of an assumed mean F factor value of 0.45. 

Measurements were made using two types of passive track-etch alpha dosimeters. One of them was the bare detector of CR-39. After exposure these dosimeters were etched by 30 % NaOH at 70°C for 5 hours. The number of pits was scored under a microscope with a television camera in Shiga University of Medical Science. Methods of calibration and adjustment for deposition of radon daughters introduced by Yonehara (Yonehara et al., 1986) were adopted. The second detectors were Terradex type SF (Alter and Price, 1972). These detectors consist of a plastic cup, covered by a filter to allow entry only of gases, with a track-etch detector inside. The reading of results was carried out by Terradex Corp. in Walnut Creek, California, U.S.A.. The measurements of radon concentration were carried out by both methods in each location, except for Hokkaido where the measurements were done only by Terradex. However, the data obtained by CR-39 detectors will be mainly presented in this paper, because the two methods did not give identical results as separately reported in this proceedings by Yonehara et al. (Yonehara et al., 1986). 

Rock, R.L., D.B. Lovett, and S.C. Nelson, Radon-daughter Exposure Measurement with Track Etch Films, Health Physics 16 617-621 (1969). 

NCRP, Report 78. Evaluation of Occupational and Environmental Exposures to Radon and Radon Daughters in the United States. National Council on Radiation Protection and Measurements, Bethesda, Md. 

Some years ago it was realized that the indoor inhalation of the short-lived radon daughters constitutes the most important contribution to the radiation exposure of the general population (Unscear, 1982). The working level concept has been introduced in the domestic environment due to the success of the concept in the occupational environment and due to a lack of experimental data on the relative and absolute magnitudes of the transformation and... 

James, A.C., Dosimetric approaches to risk assessment for indoor exposure to radon daughters, Rad. Prot. Dos. 7 353-366 (1984)... 

Reineking, A., Becker K.H. and Porstendorfer, J., Measurement of the Unattached Fractions of Radon Daughters in Houses, Presented to the Seminar on Exposure to Enhanced Natural Radiation and its Regulatory Implications, Maastricht, The Netherlands (1985). 

The risk of lung cancer from exposure to radon daughters in homes is derived by assessing lung dose, either absolutely by evaluating an effective dose equivalent (UNSCEAR, 1982 NEA, 1983) or by scaling the... 

The lung cancer risk from radon daughter exposure is known only for occupationally exposed males. In order to determine the risk in environmental situations it is necessary to determine whether the bronchial alpha dose, which confers the risk, is similar to that in mines. 

Particle size is a major factor which determines the alpha dose conversion factor for radon daughters (mGy/WLM). Data on indoor environments are emerging and indicate that a variety of specific conditions exist. For example, a dose factor four times that for a nominal occupational or environmental exposure exists if kerosene heater particles dominate the indoor aerosol and four times smaller if a hygroscopic particle dominates. 

It is important to update the bronchial dosimetry for radon daughters as new information becomes available. It is the purpose of this study to show that there is a potential for either significantly increased bronchial dose in the home per unit exposure if the ambient particle size is artificially reduced due, for example, to open-flame burning or use of kerosene heaters, or a decreased dose if hygroscopic particles dominate the indoor aerosol. 

Table II shows the nominal alpha dose factors for occupational mining exposure. Table III shows the alpha dose factors for the nominal environmental situation. Table IV shows the bronchial dose factors for the smallest sized particles, that dominated by the kerosene heater or 0.03 pm. particles. The radon daughter equilibrium was shifted to a somewhat higher value in this calculation because this source of particles generally elevates the particle concentration markedly with consequent increase in the daughter equilibrium. Table V shows the alpha dose for a 0.12 pm particle, the same as the nominal indoor aerosol particle, but for a particle which is assumed to be hygroscopic and grows by a factor of 4, to 0.5 pm, once in the bronchial tree.

The normal or average risk from whole body gamma-ray exposure in the environment is only about 10% of that from average radon daughter exposure and much less in elevated indoor environments. Considering that the radon daughter lung cancer risk can be derived directly from exposure in most cases, effective dose equivalent is an unnecessary step. 

Harley, N.H., Comparing Radon Daughter Dose Environmental versus Underground Exposure, Rad. Protection Dosimetry 7 371-375 (1984). 

Chameaud,J., Perraud,R., Lafuma,J. and R. Masse, Cancers Induced by Rn-222 in the Rat, In Proc. of Spec.Meet, on Ass, of Radon and Radon Daughter Exposure and Related Biological Effects (G.F. Clemente, A.V. Nero, F. Steinhausler and M. R. Wrenn, eds) p. 198, R.D. Press, Salt Lake City (1982). 

Cross,F.T., Palmer,R.F., Dagle,G.E., Busch,R.H., and R.L. Buschbom, Influence of Radon Daughter Exposure Rate, Unattached Fraction and Disequilibrium on Occurrence of Lung Tumors, Rad.Prot.Dosimetry 7 381 (1984). 

Edling,C., Lung Cancer and Radon Daughter Exposure in Mines and Dwellings study no. V. Linkoping University, Medical Dissertation No. 157, Dept, of Occup. Med., Linkoping, Sweden (1983). 

Lundin,F.E., Wagoner,J.K. and V.E. Archer, Radon Daughter Exposure and Respiratory Cancer, Quantitative and Temporal Aspects, Nat. Inst. Occup. Safety and Health/Nat. Inst. Env.Sciences, Joint Monograph No.1, US Dept, of Health, Education and Welfare, Public Health Service (NTIS, No. PB 204871), Washington, D.C. (1971). 

Steinhausler,F., Hofmann,W., Pohl,E. and J. Pohl-Riiling, Radiation Exposure of the Respiratory Tract and Associated Carcinogenic Risk due to Inhaled Radon Daughters, Health Physics Vol.45 No.2 331-337 (1983). 

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