Radon activity concentration

A general transport equation describing the rate of change of the radon activity concentration in the pore space results from combining the effects of diffusion and convection ... 

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... 

The radon in the air i/as measured continuously by electroprecipitation of the positively charged Po-218 ions in an electric field (10 kV) on a surface barrier detector (Porstendorfer, et al., 1980). For this purpose the air i/as dried, filtered and sucked into an aluminium sphere ( 2 1) with a flowrate of 0.5 lmin-1. The counts due to Po-218 and Po-214 were proportional to the radon activity concentration. Their disintegrations were directly detected by alpha spectroscopy with an energy resolution of about 80 keV. The monitor could detect down to 5 Bq m 3 with a two hour counting time and 30 % statistical accuracy. 

In a certain period of time there is a steady state condition in a room and a constant radon activity concentration cj(°°) could be measured. By means of this value and equations (2) (with t = 00) and (3) the actual ventilation rate of a room can be calculated ... 

Figure 2. The radon activity concentration in t i/o rooms as function of the time under different ventilation rates.

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 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. ... 

From the measured activity concentrations the ratios of the free activity to the total activity fj = cjf/cj (j = 1>2), the corresponding values of fp and the equilibrium equivalent radon concentration c q and F, respectively, were calculated. 

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 ... 

Table IJa. The aerosol concentration (Z), the activity concentrations of radon (cj) and the free (cjf, C2 ) and attached (c a, c 3, C3 ) radon daugthers, measured in rooms i/ith moderate ventilation (partly opened windows).

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. 

The subsoil is the principal source of radon in this house. Both the activity concentration of radium-226 in subsoil and of radon in soil gas are above levels for building ground that might result in significant indoor radon concentrations. The radon decay-product concentration in the dwelling before remedial measures were taken was substantially higher than the reference value of 120 mWL. 

In this analysis, it was conservatively assumed that an individual could enter a disposal site and remove a portion of the protective surface cover (about 200 m2) and expose on-site workers to the tailings.19 It was further assumed that such an unlikely scenario would occur only once in an individual s lifetime, and that exposure would occur over a period of 1,000 h. Exposure pathways considered in this analysis involve external exposure, inhalation of outdoor radon and its short-lived decay products, inhalation of particulates, and ingestion of waste. The activity concentrations of 226Ra and its decay products in the waste were conservatively assumed to be 37 Bq g 1, a... 

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 schematics of the instrument installation are shown in Fig. 9.13. The RADAIR instrument develops readouts on 4 continuous measuring channels of activity concentrations of artificial a, P, emitters and natural radon in Bq m and of the ambient y dose in pGy h. These activity concentration readouts are divided from countings in 1000 s cycles, of the activity deposited on the filter taken from samples of the surrounding air. The filter automatically advances after remaining 24 hours in front of the stack of two semiconductor detectors. The first detector located above the filter, delivers a net counting rate in proportion to the activity deposited on the filter. The... 

To convert between units of radon-222 radioactivity (Ci or Bq) and the potential alpha energy concentration (WL or J/m the equilibrium between radon gas and radon daughters must be known (See Chapter 9 for conversion formula). When radon is in equilibrium with its progeny, that is, when each of the short-lived radon daughters is present at the same activity concentration in air as radon-222, then 1 WL equals 100 pCi radon-222/L of air. However, when removal processes other than radioactive decay are operative, such as with ventilation, the concentration of short- lived daughters will be less than the equilibrium amount. In such cases an equilibrium factor (F) is applied. For example, if the equilibrium factor is 0.5, then 200 pCi radon-222/L of air is equivalent to 1.0 WL if the equilibrium factor is 0.3, then 1 WL corresponds to 333 pCi radon-222/L of air. 

The WL and the WLM have been used to describe human exposure in occupational settings for uranium and other hard rock miners. Since the WLM represents both the intensity and duration of exposure, it alone does not provide enough information to determine the actual activity concentrations of radon in the air. For example, exposure to radon and radon daughters at 1 WL (100 pCi radon-222/L of air) for 100 working months (WM) results in a cumulative dose of 100 WLMs exposure to 100 WL (10,000 pCi radon-222/L of air) for 1 WM also results in a cumulative dose of 100 WLMs. 

The amount of radon released to groundwater is a function of the chemical concentration of radium-226 in the surrounding soil or rock and in the water itself. High radon activity is associated with groundwater surrounded by granitic rock. The physical characteristics of the rock matrix are important also since it is believed that much of the radon released diffuses along microcrystalline imperfections in the rock matrix (Hess et al. 1985). Radon is rarely found in surface water due to the fact that it is rapidly released to the air when the water reaches surface levels (Michel 1987). 

The PAEC can be readily calculated once the activities of the individual radionuclides have been determined from measurements. Direct measurements of the concentrations of all short-lived decay products of Rn are difficult and limited. They are estimated from considerations of equilibrium (or disequilibrium) between Rn and its decay products. An equilibrium factor F is defined that permits the exposure to be estimated in terms of the PAEC from the measurement of radon gas concentration. This equilibrium factor is defined as the ratio of the actual PAEC to the PAEC that would prevail if all the decay products in each series were in equilibrium with the parent radon. However, it is simpler to evaluate this factor in terms on an equilibrium equivalent radon concentration, EEC. This quantity, EEC, represents the activity concentration of the radon gas that would have to exist in complete equilibrium with the decay products if the short-lived decay products had the same PAEC as in the nonequilibrium mixture. The units of EC are Bqm . ... 

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