Radon daughters activity

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... 

Jacobi, W., Activity and Potential a-Energy of Radon- and Radon-daughters in Different Air Atmospheres, Health Physics 22 441-450 (1972). 

Let us consider an atmosphere where the (activity) concentrations of radon, 222Rn, and its three short-lived daughters, 218Po, 21ifPb and 21I+Bi, are CQ, Ci, C2 and C3, the decay constants and unattached fractions of the daughter products, X, X2, X3, fi, f2 and f3 respectively, and E and E" the energies of the alpha particles from 2 8Po and 21I+Po (the fourth short(est)-lived radon daughter). 

The activity size distribution of the radon daughter aerosols. 

Figure 1. The basic processes influencing the activity balance of radon and radon daughters in houses.

The activity concentration of radon and of the free and aerosol attached radon daughters i/ere measured simultaneously. During these measurements the aerosol particle concentration i/as registered by means of a condensation nuclei counter (General Electric). 

For the determination of the free fraction the attached and the total radon daughter activity concentration were measured. The separation of the free radon daughters from the total daughter concentration was carried out by means of a high-volume diffusion screen battery (Reineking and Porstendorfer, 1986) with a 50 % penetration efficiency for 4 nm particles and for a flowrate of 2.4 m h-1. ... 

All our measurements i/ere carried out in rooms with i < 1 hr1 and the radon concentration outdoors (c 5 Bq nr 3) i/as always much smaller than indoors (cj > 100 Bq m 3). Assuming a constant radon emanation, a homogeneous activity distribution and 100 % prefiltering of the free fractions of the incoming air, the radon, the free and attached radon daughter activity concentrations indoors (cj cjf cja) and outdoors (eg c f c a) under steady conditions are ... 

Then the plateout rate qf of the free radon daughters can be determined from the activity concentration of the free Po-218 and of the radon ... 

The plateout rates of the free radon decay products on room surfaces are about 200 times higher than the values of the aerosol radon daughters and have a great influence on the radon daughter activity concentrations indoors. 

Reineking, A. and J. Porstendorfer, High-volume Screen Diffusion Batteries and the Alpha Spectroscopy for Measurements of the Radon Daughter Activity Size Distributions in the Environment, J. of Aerosol Science 17 (1986) (accepted for publication). 

By using the classical theory of ion induced nucleation to describe the growth of radon daughters from the free activity mode to the nucleation mode, we loose information about the size of the subcritical clusters. These clusters are all lumped together between the size of a pure H2O ion cluster at 75% r.h. and the size of the critical H2O-H2SO4 cluster. The model only does keep track of the growth by condensation of the radon daughters once they arrived in the nucleation mode. 

In 1975 there was a new development in the use of wire screens Sinclair and Hoopes (1975) described a diffusion battery (for measuring the particle size of aerosols) made of very fine 635-mesh stainless steel screen. An empirical equation was developed for the collection efficiency. This diffusion battery has become one of the standard techniques in aerosol measurements. Later, Sinclair et al (1978) described a screen diffusion battery configuration suited for measuring the activity - weighted size distribution of radon daughter aerosols. 

Table I. Calculated activity median diameter for attached radon daughters from measured aerosol characteristics (Tu, 1986).

The activity concentration of radon daughters is much higher than the Derived Air Concentration value of artificial radionuclides. For example, the Pu public DAC (2.4 10" Bq m ) is lower than four orders of magnitude of a mean radon daughters concentration (30 Bq m ). 

The major systemic threat of these materials is to the kidneys from biotransformed radon daughters. Radon transported by the blood reaches various tissues and organs. Its distribution depends chiefly on the fat content of organs and tissues since it is lipid soluble. From 50% to 90% of the radon body burden is located in the fatty tissues. Radon daughters taken in become localized largely in active deposits in the lungs, to which they represent a grave threat. 

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