Comparative Dosimetry of Radon in Mines and Homes (1991) / Chapter Skim
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Assessment of Exposure to the Decay Products of 222Rn in Mines and Homes
Assessment of Exposure to the Decay Products of 222Rn in Mines and Homes
Pages 20-30
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From page 20... ...
BACKGROUND In order to estimate the dose of alpha energy from inhaled radon progeny received by miners and by the general public in their homes, it is necessary to know both the concentrations of the airborne progeny and their size distributions. The size of the radioactive particles determines their penetration through the upper respiratory system and the pattern of deposition within the tracheobronchial region.
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From page 21... ...
Thus, the diffusion equivalent diameter as defined in Equation 6-1 becomes the appropriate measure of particle size. A detailed discussion of particle size and diffusion coefficient is provided in Chapter 6.
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From page 22... ...
i is the average concentration of the radon progeny during the exposure interval i expressed in WL, and ti is the number of hours of exposure at the ith concentration. The cumulative exposure in a home at a given decay product level could thus be more than four times that for an occupational exposure (8,766 total hours in a year compared with 2,000 working hours in a year)
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From page 23... ...
Because of the losses of decay products from the air by deposition on surfaces such as walls, ceilings, and furniture, the decay product activity is less than the radon activity. The term characterizing the airborne concentration of PAEC as a fraction of the radon activity is the equilibrium factor, F
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From page 24... ...
The distribution of sizes as measured based on the determination of the amounts of associated radioactivity is referred to as the activity-weighted particle size distribution. MEASUREMENT METHODS Because of limitations in the measurement methods, only two physical parameters were used in the earlier lung dosimetry models for estimating alpha doses from inhaled radon decay products: the activity median diameter of the attached radioactive aerosol and the unattached fraction of PAEC (Jacobi and Eisfeld, 1980; James et al., 1980; Harley and Pasternack, 19821.
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From page 25... ...
, who used specially developed wire screen diffusion batteries. Wire screens, which are calibrated by using a single, constant value for the typo diffusion coefficient and sampling an unattached fraction consisting of an ultrafine cluster mode in the activity size distribution, would thus be unable to separate the unattached and the attached fractions.
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From page 26... ...
, the fp value could be as high as 0.08. It is likely that the miners most highly exposed in the earliest days of underground uranium mining were probably exposed to very low unattached fractions, as the low ventilation that led to high radon concentrations would also produce high aerosol particle concentrations.
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From page 27... ...
, and the house and life-style examined did not correspond to those in the United States. To describe better the actual behavior of the airborne activity, multiple wire screens can be used in diffusion battery-type systems to comprehensively determine the activity size distribution in the 0.5- to 500-nm-diameter size range, as described by Reineking and Porstendorfer (1986)
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From page 28... ...
The presence of active aerosol sources such as a vacuum cleaner motor or burning gas burners yields an activity mode at 20 nm, with a ad of 1.5, containing approximately 10 to 15% of the PAEC. A summary of the characteristics of the radon progeny aerosols assumed by the committee is given in Chapter 3.
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From page 29... ...
1986. High-volume screen diffusion batteries and ol-spectroscopy for measurement of the radon daughter activity size distributions in the environment.
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From page 30... ...
1988. Indoor radon progeny particle size distribution measurements made with two different methods Radial.
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