Radium concentration

Several studies have been attempted to make simple correlations between radon or radium concentrations in the soil and indoor radon concentrations.4344 No significant correlations were made between these variables. 

Figure 1. Schematic illustration of factors influencing the production and migration of radon in soils and into buildings. Geochemical processes affect the radium concentration in the soil. The emanating fraction is principally dependent upon soil moisture (1 0) and the size distribution of the soil grains (d). Diffusion of radon through the soil is affected primarily by soil porosity ( ) and moisture content, while convective flow of radon-bearing soil gas depends mainly upon the air permeability (k) of the soil and the pressure gradient (VP) established by the building.

Data on the geographic distribution of surficial radium concentrations were acquired by the National Airborne Radiometric Reconnaissance (NARR) survey, part of the National Uranium Resource Evaluation (NURE) program conducted by the U.S. Department of Energy in the mid-1970s. The data were originally collected and tabulated by 1° by 2° quadrangle map area, and the data cover approximately 450 out of a total of 474 such quadrangles... 

Data on surface radium concentrations has been compiled for 394 of the 474 quadrangles covering the conterminous 48 states. The resulting distribution is illustrated in Figure 2, where the parameters shown for the distribution are calculated from the binned data. This distribution has a GM of 25 Bq kg and geometric standard deviation (GSD) of 1.75. Based on this distribution, approximately 20% of the surface radium concentration data are above 40 Bq kg and 0.7% are above 100 Bq kg... 

While these data and the resulting maps are useful in illustrating both the trends and variability in surface radium concentrations, detailed field examination of surface radium concentrations in selected areas is needed to determine the reliability of... 

Figure 2. Distribution of the surface radium concentration data from the National Airborne Radiometric Reconnaissance survey for 394 1° by 2° quadrangles covering most of the contiguous 48 states. The distribution parameters are calculated from the data and the lognormal distribution based on the geometric mean., and standard deviation from the data is shown as a solid curve.

Figure 3. Distribution of surface radium concentrations for a quadrangle (a) with a GM < 20 Bq kg and for a quadrangle (b) with a GM > 40 Bq kg. The curves represent lognormal distributions based on the distribution parameters calculated from the data.

As noted in Table I, average surface radium concentrations appear to vary by about a factor of 20. This can also be seen from the distributions from the NARR data. Soil permeabilities, on the other hand, have much larger variations, and thus, in principle, may have a greater influence on the spatial variations in average indoor radon concentrations that have been observed. As with the case of surface radium concentrations, the spatial variability of air permeabilities of soils is an important element in developing a predictive capability. 

Factors influencing the production and migration of radon in soils have been examined, and various sources of geographic data have been discussed. Two significant soil characteristics include air permeability and, less importantly, radium concentration. While there are, at present, few opportunities to compare the larger-scale data with on-site field measurements, those comparisons that have been made for both surface radium concentrations and air permeability of soils show a reasonable correspondence. Further comparisons between the aerial radiometric data and surface measurements are needed. Additional work and experience with SCS information on soils will improve the confidence in the permeability estimates, as will comparisons between the estimated permeabilities and actual air permeability measurements performed in the field. 

The main parameters determining the indoor radon concentration in detached houses are the effective radium concentration (product of the radium concentration and the emanation factor) and the permeability of the ground. The effects of other factors are not so easy to ascertain from the existing data. 

Figure 7. Radon concentration growth in the outer volume during the first fifteen hours after closure. The exhalation can is radon-tight (y= 1). The exhalation material is dry sand mixed with 11 % ground uranium ore by weight. The diffusion length, L, is 1.4 m, the sample thickness, d, is 26 cm and the outer volume height, h, is 4.0 cm. Other parameters of the sample are as follows porosity 0.47, radium concentration 1180 Bq kg, emanation fraction 0.33, bulk density 1710 kg m 3 (experiment + theory).

Initial Radium Concentration (pCi/L) Volume of Water Treated per Person Year (1000 gallons) Annual Cost per Person To Remove 1 pCi/L (dollars) Marginal Cost To Prevent One Cancer (millions of dollars)... 

After the selected ingrowth period, record the time and count the sample according to the counting procedures. The count time may be adjusted if the radium concentration is higher than usual or the detector counting efficiency is unusually high or low. 

Stewart BD, McKlveen JW, Glinski RE. 1988. Determination of uranium and radium concentrations in the waters of the Grand Canyon by alpha spectrometry. J Radioanal Nucl Chem 123 121-132. 

Figure 2 Radon loss rate from the upper 50 cm of soils versus the mean radium concentration. Bars indicate calculated 1 a error of the loss.

Radon in houses can come from building materials, the soil under the house, the water, and the domestic gas. Some materials such as alum shale and phospho-gypsum have significantly higher radium concentrations than others and can thus cause increased internal radon concentrations to increase. Ventilation rates in basements and in houses in general can reduce exposure significantly. 

In the Tri-State region of Missouri, Kansas and Oklahoma, measurements of public supply wells have shown that the U.S. Environmental Protection Agency standard for radium concentration (5pCi/l) is exceeded in a number of locations. A part of the investigation into the cause of this health hazard is the study of the uranium isotopes, U and U, precursors of Ra. 

The fresh waters of the eastern side of the area of investigation have the highest uranium concentrations and the lowest radium concentrations (Table II), Along the eastern boundary of the transitional zone, where the fresh... 

TABLE 14—Average radium concentrations of phosphogypsum samples. pCHg. 

The radium concentration in phosphogypsum in Florida averaged 21 pCi/g, and its concentration was greatest in the fine sizes. 

Total concentrations of trace elements were determined by neutron activation analyses and atomic absorption. Radium concentrations were determined by the emanation method and by the germanium-lithium counting of natural radioactivity, corrected by reference to a National Bureau of Standards (NBS) uranium ore. Chemical analyses were performed by standard methods. 

Statistical analysis of the radium data is shown in the analysis of variance (ANOVA, Table 8). At the 99% confidence level, these results show a significant difference between the radium concentrations in phosphogypsum and in the subsurface material. They show no significant differences among the cores or between the Oak Ridge and EPA results. The standard error of measurement was 4.68 pCi/g for 20 analyses. This is near the standard error of 4.S2 pCi/g... 

In this equation D (m2.s 1) represents the radon diffusivity, X the radioactive decay constant (s 1), C (Bq.m3) the radon concentration in the pore space, R (Bq.kg1) the radium concentration in the material, p (kg.m3) the bulk density of the dry material, E (dimensionless) the radon emanation power coefficient for the pore spaces, s (dimensionless) the total porosity and 0 (dimensionless) the moisture. The solution of the diffusion equation for an homogeneous medium represents the flux release from the waste material to the surface, Jt (Bq.m 2.s ). For a system without cover we obtain (Rogers, 1984) ... 

The final output for the atmospheric model is the radon concentration at a defined distance from the source, in each wind direction and in the dominant wind direction, where is considered to be located the receptor. For the hydrological model the final outputs are the radium concentration in the well water and the corresponding cumulative rate of radium transported to the well after the time considered. Local meteorological data, namely wind velocity and frequency, was used for simulating the dispersion in each octant direction. These data was obtained from a local automatic meteorological station (INAG 2004). The dominant wind direction is NW. The unknown parameters were estimated from available data. 

As stated in Section 5.2.1, soil is the primary source of radon. As such, radon is not released to soil but is the result of radioactive decay of radium-226 within the soil. The radon concentration in the soil is a function of the radium concentration, the soil moisture content, the soil particle size, and the rate of exchange of air with the atmosphere (Hopke 1987). Hopke (1987) states that normal soil-gas radon measurements are in the range of 270 to 675 pCi radon-222/L of air (10,000 to 25,000 Bq/m However, levels exceeding 10,000 pCi radon-222/L of air (370,000 Bq/m ) have been documented. 

Because radon is a gas, its occurrence in soil is most appropriately referred to as its occurrence in "soil-gas," which is in the gas or water-filled space between individual particles of soil. Factors that affect radon soil-gas levels include radium content and distribution, soil porosity, moisture, and density. However, soil as a source of radon is seldom characterized by radon levels in soil-gas, but is usually characterized directly by emanation measurements or indirectly by measurements of members of the uranium-238 series (National Research Council 1981). Radon content is not a direct function of the radium concentration of the soil, but radium concentration is an important indicator of the potential for radon production in soils and bedrock. However, Michel (1987) states that average radium content cannot be used to estimate radon soil-gas levels, primarily due to differences in soil porosity. 

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