Radium surface soils

As shown in Table I, radium content of surface soils not associated with U mining or milling varies by slightly more than an... 

Radon is a naturally occurring, chemically inert, radioactive gas. It is colorless, odorless, and tasteless. It is part of the uranium-238 decay series, the direct decay product of radium-226. Radon moves to the earth s surface through tiny openings and cracks in soil and rocks. High concentrations of radon can be found in soils derived from uranium-bearing rocks, such as pitchblende and some... 

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. 

Radon s source is a step in the transmutation of several elements uranium —> thorium — radium —> radon —> polonium —> lead. (There are a number of intermediate decay products and steps involved in this process.) Radon-222 forms and collects just a few inches below the surface of the ground and is often found in trapped pockets of air. It escapes through porous soils and crevices. 

Source. Uranium-238 is present in small amounts in most rocks and soil. Uranium has a half-life of 4.5 billion years. It decays to other elements such as radium, which breaks down to radon. Some of the radon moves to the soil surface and enters the air, whereas some remains below the soil surface and enters the groundwater. 

Unauthorized landfill disposal of uranium processing wastes (e.g., Shpack Landfill in Norton, Massachusetts, and the Middlesex Municipal Landfill in Middlesex, New Jersey) has resulted in soil contamination (Bechtel National 1984 Cottrell et al. 1981). Also, elevated uranium concentrations have been measured in soil samples collected at 30 of 51 hazardous waste sites and in sediment samples at 16 of 51 hazardous waste sites (HazDat 1998). The HazDat data includes both Superfund and NPL sites. Elevated concentrations of uranium have been detected in soil, in surface water, in groundwater, or in all three of these environmental media from these sites. In several cases, the uranium concentrations in soils were significantly elevated. For example, uranium concentrations from the Shpack/ALI site were found to be 16,460 pCi/g (24,000 pg/g). At the United States Radium Corporation site (New Jersey), uranium concentrahons ranged from 90 to 12,000 pCi/g (130-18,000 pg/g) for the Monticello site (Utah), uranium levels were reported to range from 1 to 24,000 pCi/g (1.5-36,000 pg/g) (HazDat 1998). 

Radon ( Rn) measurements made by the ARCAS provide a simple, reliable, real-time indicator of the relative maritime or continental nature of the air over coastal or oceanic areas (8). With a half-life of 3.8 days, Rn originates from the decay of Ra, a member of the decay chain. At least 98% of Rn originates from land masses (9). The radon flux at the surface depends on the radium content of the soils and rocks, the permeability of the source materials, atmospheric pressure, soil moisture, and vegetative cover (10). Relatively abrupt changes in the radon concentration over the ocean usually indicate changes in air masses and the passage of frontal systems. 

Radium adsorbed on surfaces of clay-silt particles and capillaries and microfractures of rocks is a significant source of Rn in soil gases, U mines and groundwaters. 

Radon is a naturally occurring colorless, odorless, tasteless radioactive gas that is formed from the normal radioactive decay of uranium. Uranium is present in small amounts in most rocks and soil. It slowly breaks down to other products such as radium, which breaks down to radon. Some of the radon moves to the soil surface and enters the air, while some remains below the soil surface and enters the groundwater (water that flows and collects underground). Uranium has been around since the earth was formed and has a very long half-life (4.5 billion years), which is the amount of time required for one-half of uranium to break down. Uranium, radium, and thus radon, will continue to exist indefinitely at about the same levels as they do now. 

Radon is a product of the natural radioactive decay of uranium, which occurs naturally in the earth s crust, to radium and then to radon. As radium decays, radon is formed and is released into small air or water-containing pores between soil and rock particles. If this occurs near the soil surface, the radon may be released to ambient air. Radon may also be released into groundwater. If this groundwater reaches the surface, most of the radon gas will quickly be released to ambient air, but small amounts may remain in the water. By far, the major source of radon is its formation in and release from soil and groundwater, with soil contributing the greater amount. Smaller amounts of radon are released from the near surface water of oceans, tailings from mines (particularly uranium... 

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). 

Radionuclides in soil are a source of the contamination of forage and food with radionuclides, of which strontium, cesium, and radium isotopes are the most significant. Radionuclides penetrate into plants either from the atmosphere as deposits on soil surface or through roots from the soil. Plants radio-actively contaminated are a significant hazard to man, either directly (food of plant origin) or indirectly (the milk of animals which receive contaminated forage). 

For efficient release of radon into the air spaces of soil, the radon atom must be formed within 20-70 nm of the mineral surface for most common minerals. This distance is the recoil range of a radon atom at the instant of its formation from the decay of radium. The processes by which radon atoms escape from a given material are referred to as radon emanation. The emanation power or the coefficient of emanation is defined as the ratio of the number of radon atoms that escape from the solid to the number of radon atoms formed by radioactive decay of radium in the solid. The emanation power varies from about 0.02 to 0.7, depending upon the mineral structure and the water content. 

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