Radionuclides naturally occurring, activity

Nuclear activation analysis (NAA) is a method for qualitatively and quantitatively detg elemental compn by means of nuclear transmutations. The method involves the irradiation or bombardment of samples with nuclear particles or high-energy electromagnetic radiation for the specific purpose of creating radioactive isotopes from the stable or naturally-occurring elements present. From the numbers, types and quantities of radioactive elements or radionuclides, it is possible to deduce information about the elemental compn of the original sample... 

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. 

Based on the negligible annual dose to individuals of 10 pSv and assumed scenarios for unrestricted disposal of waste, IAEA has developed recommendations on exemption levels for radionuclides in solid waste (IAEA, 1995) the recommended exempt concentrations have values in the range of about 0.1 to 104 Bq g 1 depending on the radionuclide. IAEA also has issued recommendations on total activities and activity concentrations of radionuclides that could be exempted from any requirements for notification, registration, or licensing of sources or practices, based on the same exemption principles and assumed scenarios for exposure of the public (IAEA, 1996). The recommended exemption levels for naturally occurring radionuclides are limited to their incorporation in consumer products, use as a radioactive source, or use for their elemental properties. 

If secular equilibrium is not established, the activities of succeeding radionuclides can also be calculated by use of the equations given in this section. An example is the decay of the naturally occurring Po ( Po " Pb °Pb...). The... 

In some cases, technology helps to reduce the natural radiation exposure. For example, when drinking water supplies are drawn from surface waters, the use of water-purification processes brings about a decrease in the concentration of radium and other naturally occurring radioactive elements. Another example is the burning of fossil fuel, which reduces the specific activity of C in the biosphere and therefore lowers the doses from those radionuclides. 

Coal, like most materials found in nature, contains trace quantities of the naturally occurring primordial radionuclides. Therefore, the combustion of coal results in the release to the environment of some natural activity and in the re-distribution of that natural activity from deep in the earth to locations where it can modify ambient radiation fields and population radiation exposure. 

Polycyclic Aromatic Hydrocarbons PAH compounds are naturally occurring, but human activities can increase the concentrations in the environment. Soil samples were collected to study PAH compounds. The core sections were dated using radionuclides to determine when each section was deposited. 

Numerous separation methods of the types cited in Chapter 3 were developed and applied in radioanalytical chemistry during the past century. The hrst 30 years were devoted mostly to nuclear chemistry applications for identifying and characterizing the naturally occurring radionuclides. In the following years, attention shifted to the man-made ones these activities continue, as exemplified by the work described in Chapter 16. Currently, many methods are devoted to monitoring radionuclides in the environment, facility effluent, process streams, and workers. 

The long-lived radionnclides associated with nnclear fission and concomitant nen-tron activation are listed in Table 6.1, together with the long-lived terrestrial radionuclides and the major cosmic-ray-indnced radionnclides in nature. Of the fission and activation products in Table 6.1, all bnt the minor ones are commonly measured of the naturally occurring radionnclides, " K, nraninm, thorinm, and radium are frequently encountered in samples, together with radioactive progeny of the latter three. 

Recent experience at DOE sites has shown that most of the environmental samples collected today are levels C and D. Hence, the laboratory under consideration in this chapter is designed for the analysis of levels C and D samples. These are environmental or bioassay samples that contain radionuclides at low concentrations, i.e., approximating levels of naturally occurring radionuclides. Samples at levels A and B generally will be analyzed in on-site government laboratories for a variety of reasons, i.e. transportation restriction, sample assay limitations, sample security, and national security. In Table 13.1, the authors provide their suggested activity levels to match the four categories identified by the DOE. 

LSA material is that which has by its nature a limited specific activity. It is divided into three groups (1) LSA-I includes ores or naturally occurring radionuclides, unirradiated natural or depleted uranium, and other low activity radioactive materials (2) LSA-II includes certain concentrations of tritium and solids, liquids, and gases with no more than 10,000 to 100,000 times less activity than A2 per gram and (3) LSA-III includes solid materials that are imbedded in a binder, relatively insoluble, and with not more than 500 times less activity than A2 per gram. 

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