Radon pore space

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 ... 

This formulation is based on several assumptions, including one of small soil moisture content (meaning that negligible radon is dissolved in liquid in the pore space). Other simplifying... 

To measure the radon concentration in pore spaces of the walls, holes were drilled to a depth of 10 cm to accommodate 12 mm copper... 

Note that % is the concentration of radon in the pore spaces per m3 of soil. The concentration per m3 of interstitial air in the soil is / , where e is the porosity of the soil. Equation (1.2) gives... 

Compared to this idealized model, the actual flux of Rn may be diminished by the saturation of pore space by water (the mean length of Rn diffusion in water is on the order of a milhmeter, so saturation diminishes the flux by up to a factor of 1,000) and decreases in porosity with depth. Advection of gas through soil in response to barometric pressure change, soil gas convection, and transpiration of Rn saturated soil solution will increase the radon escape rate. All of these processes are difficult to model accurately, so the determination of Rn fluxes rehes on measurements. 

Radon ( Rn or Rn) is a radioactive noble gas, which is chemically relatively inert. The gas originates from traces of uranium or U) in various materials, e.g. granites. The Rn atom is formed in the mineral grains of the material. A certain fraction of atoms formed escapes into the material pore space and diffuses to the material surface to be released in to the surrounding air. 

The vapors of volatile contaminants, such as radon and volatile organic compounds, can be transported through diffusion from the soil pore spaces into buildings. Three principal factors are needed to define the ratio of contaminant concentration in indoor... 

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) ... 

In soil, radon is transported primarily by alpha recoil and mechanical flow of air and water in the soil. Alpha recoil is the process by which radon, when it is formed by radium emitting an alpha particle, actually recoils in the opposite direction from the path of particle ejection. After radon is released into the pore spaces, its ultimate release to ambient air is a function of the soil porosity and meteorological factors, such as precipitation and atmospheric pressure. Once radon is released to ambient air, its dispersion is primarily determined by atmospheric stability, including vertical temperature gradients and effects of wind. 

Emanation is the process by which radon is transported from a solid to a gas or liquid medium. At the soil particle level, radon gas is transferred from soil particles into pore spaces (gas- or liquid-filled spaces between soil particles) primarily by alpha recoil. Alpha recoil occurs after radium decays by emitting an alpha particle. After the particle is ejected, the resulting radon atom actually recoils in the opposite direction. Alpha recoil results in breaking of chemical bonds in the solid. 

Once radon enters the pore space, it is transported by diffusion, co nvection, and flow of rain and groundwater. The diffusion constant for radon is approximately 10 cm per second in air and 10 cm per second in water (WHO 1983). These constants indicate that diffusion of radon is a relatively slow process and that its movement is, therefore, primarily accomplished by mechanical transport of air and water in the pore space. 

The actual release of radon from the pore space or soil-gas to ambient air is called exhalation. The rate of this process is a function of many variables including the concentration of radon in the soil-gas, the soil porosity, and meteorological factors such as precipitation and variations in atmospheric pressure (WHO 1983). 

The fraction of radon atoms released into rock or soil pore space from a radium-bearing grain is called the emanation coefficient (also called emanation factor or emanating power). Typical emanation coefficients for rocks and soils range from 0.05 to 0.7. The grain size, the shape, and the soil moisture are important factors. 

Radon is produced by radium decay in ore bodies and by recoil emanating from the solid matrix of the material into the air- or water-filled pore space, or into fractures in rocks. In underground mines radon is transported from the rocks to the galleries by diffusion and convection through water or air circulation. The importance of each one of these processes depends on the geological and tectonic fractures of the formation and the hydrologic behavior of the aquifer. 

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