Radon progeny

Steinhausler (1987) and Martell (1987) review the dosimetric models and related model studies. Their view is that there are still very large uncertainties in the existing data and in the extrapolation from the exposure and response data for underground miners and experimental animals to the health effects of the radon progeny levels to which the general public is exposed. B.L. Cohen (1987) describes his work to relate radon measurements with lung cancer rates for various geographical areas to test the concept of a dose threshold. 

Bandi, F., A. Khan, and C.R. Phillips, Effects of Aerosol Poly-dispersity on Theoretical Calculation of Unattached Fractions of Radon Progeny, this volume (1987). 

Knutson, E.O., A.C. George, L. Hinchliffe, and R. Sextro, Single Screen and Screen Diffusion Battery Method for Measuring Radon Progeny Size Distributions, 1-500 nm, presented to the 1985 Annual Meeting of the American Association for Aerosol Research,... 

Kulju, L.M., K.D. Chu, and P.K. Hopke, The Development of a Mobility Analyzer for Studying the Neutralization and Particle Producing Phenomena Related to Radon Progeny, this volume (1987). 

Martell, E.A., Critique of Current Lung Dosimetry Models for Radon Progeny Exposure, this volume (1987). 

Measurements of radon progeny, which are the more difficult to make, can be replaced with measurements of radon to provide information on the upper limit for the potential alpha energy exposure from radon progeny. Therefore, simple passive radon monitors for integrated measurements of 1 to 12 months (Alter and Fleischer,... 

After the end of the 4-day exposure, the detectors were returned to EML for analysis. The amount of radon adsorbed on the carbon device was determined by counting the gamma rays of radon progeny in equilibrium with radon. The concentrations of radon in the buildings were determined from the radioactivity in the device and the calibration factor, obtained in a radon chamber, that takes into consideration the length of exposure and a correction for the amount of water vapor adsorbed during the exposure. The lower limit of detection with this technique is 0.2 pCi/1 for a measurement period of 4 days when the test sample is counted for 10 min, 4 days after the end of exposure. More than 90% of the radon monitoring devices were analyzed successfully. Most of the unsuccessful measurements were due to delays or losses caused by the participants. 

Numerous radon and radon decay measurements in houses are now being made by a large number of private and governmental organizations. In order to assure valid and consistent measurements, it is important that proven methods be used following standardized procedures. To address this need, EPA issued "Interim Indoor Radon and Radon Decay Product Measurement Protocols" and established a Radon/Radon Progeny Measurement Proficiency program. 

Singletary, H.M., Starner, K., and Howard, E., Implementation Strategy for The Radon/Radon Progeny Measurement Proficiency Evaluation and Qualtiy Assurance Program, EPA 5201.-86-03, U.S. Environmental Protection Agency, Washington, D.C. (February 1986). 

Effects of Aerosol Folydispersity on Theoretical Calculations of Unattached Fractions of Radon Progeny... 

Theoretical calculations of unattached fractions of radon progeny require prediction of an attachment coefficient. Average attachment coefficients for aerosols of various count median diameters, CMD, and geometric standard deviations, ag, are calculated using four different theories. These theories are ... 

In addition to the quasi-steady state assumption, the other assumptions required to arrive at equation (1) are 1. the aerosol itself does not coagulate 2. there is a fully developed concentration gradient around each aerosol particle and 3. the concentration of unattached radon progeny atoms is much greater than the concentration of aerosol particles (in order that concentration gradients of radon progeny atoms may exist). This last assumption is usually not valid since the radon progeny concentration is usually much less than the aerosol concentration. 

From equation (1) it can be seen that application of the diffusion theory leads to the conclusion that the rate of attachment of radon progeny atoms to aerosol particles is directly proportional to the diameter of the aerosol particles. 

The kinetic theory of radon progeny attachment to aerosol particles assumes that unattached atoms and aerosol particles undergo random collisions with the gas molecules and with each other. The attachment coefficient, 3(d), is proportional to the mean relative velocities between progeny atoms and particles and to the collision cross section (Raabe, 1968a) ... 

When the radius of an aerosol particle, r, is of the order of the mean free path, i, of gas molecules, neither the diffusion nor the kinetic theory can be considered to be strictly valid. Arendt and Kallman (1926), Lassen and Rau (1960) and Fuchs (1964) have derived attachment theories for the transition region, r, which, for very small particles, reduce to the gas kinetic theory, and, for large particles, reduce to the classical diffusion theory. The underlying assumptions of the hybrid theories are summarized by Van Pelt (1971) as follows 1. the diffusion theory applies to the transport of unattached radon progeny across an imaginary sphere of radius r + i centred on the aerosol particle and 2. kinetic theory predicts the attachment of radon progeny to the particle based on a uniform concentration of radon atoms corresponding to the concentration at a radius of r + L... 

In calculating 3(d) using Fuchs theory, D and v for radon progeny are used as above. It is also assumed that the aerosol particles are spherical and of unit density. It may be noted that assuming a higher density for the aerosols does not change the results appreciably. Fuchs model is calculated for... 

Fuchs model the radius and mass of the radon progeny are 4.9 x 10 8 cm and 5.46 x 10 22 g, respectively, for the above mentioned values of D, v and the other parameters. These calculated values are higher than would be expected for 218Po, suggesting that clustering occurs. 

In order to calculate the theoretical unattached fraction of radon progeny the appropriate differential equations must be developed to describe the net formation of unattached radon progeny. The system may be visualized schematically for RaA as illustrated in Fig. 2. It is assumed that there is no flow into or out of the system or removal by electric fields. The equations which describe the system presented in Fig. 2 are ... 

The rate of attachment of radon progeny to aerosols, X, is expressed as ... 

The most complete theory for aerosol coagulation is that of Fuchs (1964). Since the attachment of radon progeny to aerosols can be considered as the coagulation of radon progeny (small diameter particle) to aerosols (large diameter particle), it is reasonable to use Fuchs theory to describe this process. The hybrid theory is an approximation to Fuchs theory and thus can be used to describe the attachment of radon progeny to aerosols over the entire aerosol size spectrum. 

If it is accepted that the hybrid theory is the most complete theory for attachment of radon progeny to aerosols, the magnitude of the error involved in using exclusively either the kinetic or the diffusion theory can be seen from Figs. 3-7 and Table III. 

Unattached fractions of RaA (at t = °°) for two mine aerosols and for a typical room aerosol are shown in Table III. It is usually assumed that the attachment of radon progeny to aerosols of CMD < 0.1 ym follows the kinetic theory. In Table III it is apparent that the hybrid and kinetic theories predict similar unattached fractions for monodisperse aerosols. However, for more polydisperse aerosols, the kinetic theory predicts lower unattached fractions than the diffusion theory and thus the diffusion theory is the more appropriate theory to use. It is also evident that the kinetic-diffusion approximation predicts unattached fractions similar to those predicted by the hybrid theory in all cases. 

Calculation of the attachment coefficient is required for theoretical prediction of the unattached fraction of radon progeny. The hybrid theory, which is a form of Fuchs theory with certain justifiable assumptions, can be used to describe attachment to aerosols under all conditions of Og and CMD. 

The accuracy of the measurement of radon concentrations with bare track detectors was found to be unsatisfactory due mainly to the changes of the deposition rate of radon progeny onto the detector as a result of air turbulence. In this work, therefore, a method was developed which can correct the contributions of the deposition to the track densities by classifying the etched tracks according to their appearance, i.e. round or wedge shaped. Using this method, about 30% improvement in the error of measurements was achieved. The calibration coefficient ob tained by experiment was 0.00424 tracks/cm /h/(Bq/m ), which agreed well with the calculated value. Comparison was also made of the present method with other passive methods, charcoal and Terradex, as to their performance under the same atmosphere. 

The radon progeny Working Levels for calculation of activity distributions were calculated using the equation ... 

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