Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials (1999) / Chapter Skim
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2 Natural Radioactivity and Radiation
2 Natural Radioactivity and Radiation
Pages 25-60
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From page 25... ...
Natural radiation comprises cosmic radiation and the radiation arising from the decay of naturally occurring radionuclides. The natural radionuclides include the primordial radioactive elements in the earth's crust, their radioactive decay products, and radionuclides produced by cosmic-radiation interactions.
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Tables 2.1 and 2.2 also show typical concentrations in various environmental media. 2In nature, 235U and a few other nuclides of uranium and thorium undergo fission spontaneously or as a result of interactions with neutrons that originate in cosmic rays or other natural sources.
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and NuDat online database maintained by Brookhaven National Laboratory, September 9, 1997.
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28 Table 2.1 (continued) NATURAL RADIOACTIVITYAND RADIATION Radio- Half- Major Target nuclide life Radiations Nuclides Typical Concentrations, Bq/kg AirRain Water Ocean (troposphere)
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and NuDat online database maintained by Brookhaven National Laboratory, September 9, 1997.
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30 Table 2.3 Uranium-238 Chaina NATURAL RADIOACTIVITYAND RADIATION Nuclide Historical Name Half-life Major Radiations 23su Uranium I 4.47 x 109 y a, < 1% y aData from NuDat online database maintained by Brookhaven National Laboratory, September 9, 1997. Minor branches, <1%, not shown.
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208TI (36%) Thorium C' / 0.300 ms I a / ,B, Thorium C'' 3.05 m 208pb Thorium D Stable None 31 aData from the NuDat online database maintained by Brookhaven National Laboratory, September 9, 1997.
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From page 32... ...
(1.38%) Aetinium K 22.0 m 223Ra Aetinium X 11.44 d a, 2~9Rn Aetinon 3.96 s a, 2.5po Aetinium A 1.78 ms a, < 1% 2'~Pb Actinium B 36.1 m 0,y 2"Bi Actinium C 2.14 m a, ~y 2o7Tl Actinium C' 4.77 m 0, e 1% 2o7pb Actinium D Stable None aData from NuDat online database maintained by Brookhaven National Laboratory, September 9, 1997.
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From page 33... ...
Regulations for controlling exposure of the public to radionuclides are often dose-based. Because the doses result from interaction of humans with radionuclides contained in environmental media air, water, soil, and biota a knowledge of the behavior of naturally occurring radionuclides in these media is needed (Landa 1980~.
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Occurrence and Doses Uranium is found in all rocks and soils. Typical concentrations in the more prevalent types of rock and average concentrations in the earth's crust and in soil are listed in table 2.6.
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GUIDELINES FOR EXPOSURE TO TENORM 35 Table 2.6 Rangesa and averages of concentrations of 40K, 232Th, and 238U in Typical Rocks and Soilsb Material 40K 232Th 238u %total K Bq/kg ppm Bq/kg ppm Bq/kg Igneous rocks Basalt 0.8 300 3-4 10-15 0.5-1 7-10 (crustal) 1.1 300 2.7 10 0.9 10 Mafic Salic 4.5 1400 20 80 4.7 60 Granite(crustal)
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From page 36... ...
. Radium-226 Radium-226 and its decay products, members of the uranium chain, are responsible for a major fraction of the internal dose received by humans from the naturally occumng radionuclides (IAEA 1990)
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GUIDELINES FOR EXPOSURE TO TENORM 37 Radium does not form discrete minerals but can coprecipitate with many minerals, including calcium carbonate, hydrous ferric oxides, and barite (Basted. Radium can be sorbed by clay minerals, colloidal silicic acid, manganese oxides, and organic matter.
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Persons consuming water that contains 226Ra at 0.2 kBq/m3 (5 pCi/L) at 2 L/d would receive an annual effective dose equivalent of about 50 ,uSv (5 mrem)
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The external dose rate due to gamma radiation from the thorium chain is usually somewhat greater than that from the uranium chain and arises primarily from the decay products rather than from 232Th itself. The internal
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The geochemistry of 228Ra is essentially identical with that of 226Ra.228Ra and its decay products are estimated to contribute annual dose equivalents of 300 pSv (30 mrem) to cortical bone, 84 pSv (8.4 mrem)
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From page 41... ...
However, some of the dust particles will be deposited in the respiratory system. Additional radon decay products will be deposited with each breath until radioactive equilibrium is reached, at which point the amount of activity deposited per unit time equals the amount eliminated from the lungs by the combination of physiologic clearance and radioactive decay.
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In EPA's draft report on diffuse NORM waste (EPA 1993b) , a diffusion model is used to estimate indoor radon concentrations on the basis of 226Ra concentrations in waste on which a house was built.
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44 NA TURAL RADIOS CTIVITYAND RADIA TION o0 O '/~ ~0 to t-~]
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GUIDELINES FOR EXPOSURE TO TENORM CO CO 45 lo Cal A lo CD 1 coil lo 1 o O O Cal L ~ _ (D _ ~ fir Lo ~ L Jar ~ L CY)
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From page 46... ...
In the 1992 Lawrence and others study, performed in Colorado, estimates of the concentration of indoor radon attributed to radon in the domestic water supply depended on assumptions regarding the fraction of radon emanating from the water and on dwelling ventilation rates. The averages of the
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From page 47... ...
. The mean residence time of dust suspended in the troposphere is about 15 d, so there is little time for typo to be formed in suspended dust, and the concentration of typo near ground level is smaller than that of 2~0Pb.
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The tissue content of these nuclides in Lapps in northern Finland, who subsist on caribou, was about 12 times that of residents of southern Finland, where normal Scandinavian dietary regimes exist (Persson 1972; Kauranen and Miettinen 19694. Potassium-40 Of the three naturally occurring potassium isotopes, only 40K is unstable, having a half-life of 1.3 x 109 y.
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. NATURAL SOURCES OF EXTERNAL IONIZING RADIATION The dose received from external sources of ionizing radiation originates in cosmic rays and photon-emitting radionuclides in the earth's crust (terrestrial sources)
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GUIDELINES FOR EXPOSURE TO TENORM Cal [ o = o ~ no c, ~o .
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Diurnal variations in radon concentration are caused by diurnal changes in atmospheric stability. Rainout of radon decay products briefly increases the dose rate, whereas accumulated soil moisture decreases it as a result of attenuation of the gamma-ray flux.
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From page 55... ...
existed briefly at altitudes as low as 10,000 m (Schaefer 1971~. SUMMARY OF HUMAN EXPOSURES TO NATURAL IONIZING RADIATION The annual effective dose equivalent received by persons living in areas of normal background radiation is estimated at 2.4 mSv (240 mrem)
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56 NATURAL RADIOACTIVITYAND RADIATION ABSORBED DOSE RATE IN AIR ( mGyly )
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GUIDELINES FOR EXPOSURE TO TENORM Table 2.9 Estimated Effective Dose Equivalents From Natural Sources in Normal Regionsa Source 57 Annual Effective Dose Equivalent mrem mSv External Internal Total External Internal Total -- 0.36 0.015 0.015 Cosmic, including neutrons Cosmogenic nuclides Primordial nuclides 40K 87Rb 238U chain 238U ~ 234U 230Th 226Ra 222Rn ~ 214Pb 2l0Pb ~ 210po 232Th chain 232Th 228Ra = 224Ra 220Rn = 208Pb Total (round) aAdapted from UNSCEAR (1988)
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· Doses received by humans from sources of natural radiation in the environment are quite variable, with a range of a factor of about 4 for external sources except radon and about 20 for radon. As a practical matter, the implications of existing levels and the variability of natural radionuclides and doses received by humans should receive careful consideration as efforts to regulate TENORM are contemplated.
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