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Radon, Part 1

Radon, Part 1. GLY 4241 - Lecture 10 Fall, 2014. Radiation. Radiation is one of many areas that have become of concern to environmental scientists Radiation comes from two sources Natural processes Man. Natural Radioactivity. Two kinds

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Radon, Part 1

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  1. Radon, Part 1 GLY 4241 - Lecture 10 Fall, 2014

  2. Radiation • Radiation is one of many areas that have become of concern to environmental scientists • Radiation comes from two sources • Natural processes • Man

  3. Natural Radioactivity • Two kinds • Short lived nuclides formed by cosmic ray interactions with the atmosphere • Long lived isotopes that have persisted since planetary formation • May be concentrated by natural or anthropogenic processes

  4. Common Long-Lived Isotopes • Uranium • 235U • 238U • Thorium • 232Th • All decay to yield isotopes of lead

  5. 232Th Decay Series

  6. 235U Decay Series

  7. 238U Decay Series

  8. Properties of Radon • Colorless, odorless gas • Soluble in both water and organic solvents • Atomic number 86 • Permissible Concentration • 0.4 x 10-2 picoCuries/cm3, or 4 pCi/liter • One curie is the number of disintegrations per second of one gram of radium, or 3.7 x 1010 disintegrations per second

  9. Radon Isotopes

  10. Sievert • Another unit in use is the sievert (symbol: Sv), named after Rolf Sievert, a Swedish medical physicist • It is the SI derived unit of dose equivalent, which attempts to reflect the biological effects of radiation as opposed to the physical aspects • The worldwide average human exposure from natural sources of radiation is 2.4 millisieverts (mSv) per year • About half comes from the radioactive decay products (mostly α-particles) of radon gas, with most of the remaining natural exposure comes from cosmic rays and terrestrial gamma-rays

  11. Human Radiation Exposure From Little, 2003

  12. Radiation Exposure from Radon • Based on data from the United Kingdom • About half of human radiation exposure in the UK is from radon

  13. Isotopes of Concern • Two isotopes are of particular concern, the the alpha emitters 220Rn and 222Rn • Alpha particles are the nuclei of 4He atoms • They are heavy and are emitted with a great deal of energy • Although they are not very penetrating, being stopped by a piece of paper, they do a great deal of damage if they disintegrate within a cell • The alpha particles from 220Rn and 222Rn ionize about 250,000 and 180,000 atoms, respectively, per distintegration

  14. Beta Emitters • Beta emitters cause less localized damage • Beta particles are electrons • They are negatively charged and are repelled by the other electrons of ions and atoms • A 6 Mev beta particle travels about 3 centimeters in biological tissue • Beta emitters are dangerous externally and internally

  15. Radon Nomenclature • The isotope 220Rn is sometimes called Thoron since it is a daughter of Thorium • Radon is sometimes used to refer to the isotope 222Rn alone, but this usage can be confusing and will not be used in this course

  16. Biological Effects of Ionizing Radiation • A single ionization in a nucleic acid canalter the genetic instructions for assembling the protein constituents of the cell • Certain kinds of alteration, or combinations of alteration, are believed to be carcinogenic • A well-known correspondence between radiation exposure and cancer exists • In biological tissue, an alpha particle travels about 0.05 millimeters before stopping

  17. Relative Rn Risk

  18. Assessing Risk • “ ‘The risk estimates obtained in this study suggest that cumulative [total] radon exposure in the residential environment is significantly associated with lung cancer risk.’ • After adjusting for age, smoking, and education, and using categorical radon exposure levels, a 15 year exposure at levels equivalent to EPA's action level of 4 pCi/L yielded excess odds of 0.50 i.e., an increase in lung cancer risk of 50% (95% confidence interval: 0.004, 1.81) for total cases and excess odds of 0.83 for cases with personal interviews i.e., an increase in lung cancer risk of 83% (95% confidence interval: 0.11, 3.34). • The higher risk found for cases with personal interviews vs. the total cases most probably reflects the more accurate exposure assessment obtained from interviews with cases vs. interviews with relatives.”

  19. Julia Harris Video

  20. Radon Parental Material • Rn is a daughter of uranium or thorium, and is usually associated with rocks that contain significant quantities of U and/or Th • Both U and Th are lithophile elements • Strongly lithophile elements prefer the silicate or oxide phases over sulfide or metallic phases • In the silicates and oxides, they exhibit ionic bonding

  21. Ionic Radii of Th and U • All radii in nm

  22. Uranium Minerals • Uraninite (UO2) • Carnotite (K2(UO2)2(VO4)2•3 H2O) • Tyuyamunite (Ca(UO2)2(VO4)2 •5-8½ H2O) • Torbernite (Cu(UO2)2(PO4)2 •8-12 H2O) • Autunite (Ca(UO2)2(PO4)2 •10-12 H2O)

  23. Thorium Minerals • Thorianite (ThO2) • Thorite (ThSiO4)

  24. Carnotite Associated with Wood

  25. Carnotite in Shale • A layer of yellow Carnotite that is sandwiched in between layers of a soft shale • Anderson Mine, Yavapai County, Arizona, U.S.A. 

  26. Forsterite Hydrolysis • Examples include the hydrolysis of the silicate olivine (forsterite) to yield silicic acid and magnesium ion

  27. Plagioclase Feldspar Hydrolysis • Hydrolsis reaction from albite to the clay mineral kaolinite

  28. Sulfide Minerals • Pyrite, FeS2, is the major sulfide present • Many minor elements are enriched in black shales, including V, U, As, Sb, Mo, Cu, Ni, Cd, Ag, Au and platinum group metals • Concentration of U • Correlates with increasing C in some smaples • Also correlates with grain size • And in phosphatic shales

  29. Phosphoria Formation • The Western Phosphate Field is a 350,000 km2 area of the northern Rocky Mountains • Darkened areas represent exposures of the Phosphoria Formation.

  30. U in Coal • Coal consists almost entirely of organic hydrocarbons • Organic geopolymers, modified by hydrolysis and microbial degradation • Microbes often concert sulfates to sulfides • Some products are easily broken down • Others, often porphyrins, are quite resistant

  31. Metal Enrichment in Coal • Coal is often rich in sulfur, uranium, and vanadium • Some coals have been used as ores of vanadium • Radon levels in coal mines are often elevated • Levels of 1650 Becquerels/m3 were found in a Brazilian mine in operation since 1942 • This is about 11 times the maximum exposure level in indoor air, and is higher than levels permitted in mines in most countries

  32. Thorium • Does not show multiple oxidation states • Found primarily in felsic igneous rocks and the immediate weathering products of these rocks • It is usually unaltered by chemical weathering, although physical weathering may reduce the grain size • Much uranium is also found in the same environment.

  33. Th and U Content in Selected Rocks • All data are in parts per million (ppm)

  34. Ra Concentrations in Selected Igneous Rocks and Resulting Radioactivity

  35. Ra Concentrations in Selected Non-Igneous Rocks and Resulting Radioactivity

  36. New Hampshire Radon Levels • Radon Levels by Town

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