Radioactive elements in soils

Linsalata P, Penna Franca E, Sachett I, et al. 1987. Radium, thorium, and the light rare earth elements in soils and vegetables grown in an area of high natural radioactivity. DOE Symp Ser 59 131-146. 

After Julius Elster and Hans Geitel had noticed that the electrical conductivity of the air in caves and closed cellars is higher than that in the free atmosphere, they finally found that this was caused by the presence of emanations, or radioactive gases, in the ground. In a series of investigations from 1901 to 1906 they demonstrated the presence of radioactive elements in various kinds of rocks and soils, and showed that minute amounts of both radium and thorium are widely distributed in the earth s crust, in spring waters, in sea water, and in the atmosphere (85, 96). 

The nuclear bombs over Hiroshima and Nagasaki, and the later atmospherical detonations created a new type of soil problems. Radioactive elements in the air came with time into the soil, were later taken up by the plants and thus became dangerous in animal and human nutrition. 

Throughout the world comprehensive investigations on quantities of radioactive fall-out took place. Because most of these registrations were carried out by military authorities only few of the results have been published. Investigations started to find out how to prevent or diminish the injurious effects. For example, other compounds were added to the soil to reduce the uptake of radioactive elements in plants. The results from this type of investigations were published to a greater extent. 

Baranov, V.l., Morozova, N.G., Akimova, T.G. and Orlova, A.V., 1968. Naturally radioactive elements in surface and soil groundwaters. Geokhimiya, 3 334-340 (in Russain). 

Natural radioactivity is formed particularly by long-lived isotopes, i.e. by those with half-lives of 10 to 10 years. These isotopes are usually widely scattered in the soil. The activity level depends particularly on contents of uranium, thorium, radium and potassium the radiation energy of these elements represents as much as 98% of the total energy of radiation of all the natural radioactive elements in the soil. 

Cobalt, Co, is a metallic element. Cobalt 59 is the only stable isotope. Common isotopes are cobalt 57, cobalt 58, and the most common, cobalt 60. Cobalt is a steel-gray, shining, hard, ductile, and somewhat malleable metal. It has magnetic properties and corrodes readily in air. Cobalt dust is flammable and toxic by inhalation, with a TLV of 0.05 mg/m of air. It is an important trace element in soils and animal nutrition. Cobalt 57 is radioactive. It has a half-life of 267 days. It is a radioactive poison and is used in biological research. Cobalt 58 is also radioactive and has a half-life of 72 days. It is a radioactive poison, and it is used in biological and medical research. Cobalt 60 is one of the most common radioisotopes. It has a half-life of... 

People receive some radiation exposure each day from the sun, radioactive elements in the soil and rocks, household appliances like television sets and microwave ovens, and medical and dental x-rays. 

EDXRF analyzer (hand-held or transportable. X-ray tube or radioactive isotope source) for elements in soils... 

Plutonium (Pu) is an artificial element of atomic number 94 that has its main radioactive isotopes at 2 °Pu and Pu. The major sources of this element arise from the manufacture and detonation of nuclear weapons and from nuclear reactors. The fallout from detonations and discharges of nuclear waste are the major sources of plutonium contamination of the environment, where it is trapped in soils and plant or animal life. Since the contamination levels are generally very low, a sensitive technique is needed to estimate its concentration. However, not only the total amount can be estimated. Measurement of the isotope ratio provides information about its likely... 

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

This very long half-life (1.25x1(r years) isotope comprises 0.0117 percent of all potassium. Thus, this isotope is present in all of us and has always been so. In addition, the materials around us, including the soil and the building materials, contain both potassium and the heavy naturally occurring radioactive elements thorium and uranium that contribute to a level of radiation to which we are all continuously exposed. Thus, there is always radiation exposure to the general public and we must understand the exposure due to radon in this context. The amount of radioactivity is described in units of activity. The activity is the number of decay events per unit time and is calculated as follows... 

Selders, A. A., Cline, J. F. and Rediske, J. H. (1956). Uptake of radioactive elements from Bravo test site soil, page 87 in Biology Research—Annual Report (for) 1955, Report No. HW-41500 (Office of Technical Services, Washington). 

The proposal was fatally flawed by failing to address some of the most critical elements of soil washing. Soil washing is essentially a hydraulic flotation process which removes the fines from the soil. Depending upon the soil, that can account for between 5% and 15% of the volume processed. The process is strictly one of density settling and stokes law is followed in the separation process. What you wind up with is a clean and sterile soil because the organic materials in the soil have a density of between 1.2 and about 2.0 and the clays, and some of the silts, because of their particle size are removed from the soil. In the case of Belarus soils, this also removed about 60%-80% of the fine radioactive materials, but that was not the problem. The problem was one of scale and residuals. 

DeCaF treats soil, sludges, solids (e.g., slag), residues, and sediments contaminated with radioactive elements and other hazardous constituents. The technology has potential applications in the treatment of heavy metals. The technology can treat uranium-contaminated calcium fluoride matrices, rare-earth ore residues, and fluorspar contaminated with uranium. The technology can also extract more complex fluoride by-products. 

Touring the formation of radioactive fallout particles, one of the most important processes is the uptake, in the cooling nuclear fireball, of the vaporized radioactive fission products by particles of molten soil or other environmental materials. Owing to the differences in the chemical nature of the various radioactive elements, their rates of uptake vary, depending upon temperature, pressure, and substrate and vapor-phase composition. These varying rates of uptake, combined with different residence times of the substrate particles in the fireball, result in radiochemical fractionation of the fallout. This fractionation has a considerable effect on the final partition of radioactivity, exposure rate, and radionuclides between the ground surface and the atmosphere. 

In an early study by Schery and Gaeddert (1982), an accumulator device was used to measure the effect of atmospheric pressure variations on the flux of Radon (222Rn), an inert radioactive element with a half-life of 3.8 days, from the soil. Fluxes measured by the accumulator were compared with predictions for flow-free diffusion from a model developed by Clements and Wilkening (1974), which applies Fick s law. A mean 222Rn-flux enhancement of about 10%, with a high value of 20%, due to cyclic atmospheric pressure variations was observed. However, the device s effectiveness was limited by back diffusion from the accumulator to the subsurface, leading the authors to view the flux values as semi-quantitative. 

Tome, F. V., Rodriguez, M. P. B., and Lozano, J. K. (2003). Soil-to-plant transfer factors for natural radionuclides and stable elements in a Mediterranean area. J. Environ. Radioact. 65, 161-175. 

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