Radiological Emergency Management Independent Study Course 5-4 Terrestrial Radiation Terrestrial radiation accounts for over three-quarters of the overall dose from natural sources of radiation. Three main types of terrestrial radiation account for most of this: 1. Rocks and minerals. 2. Radon and its decay products. 3. Activity in food. Rocks and Minerals The main sources of radiation in rocks are Potassium-40 and the two series of radioactive elements that come from the decay of Uranium-238 and Thorium-232. Uranium-238 is dispersed throughout the soil at various low levels of concentration. Where the concentration exceeds 1,000 ppm, it may be economic to mine the ore to make fuel for nuclear reactors. Thorium-232 is similarly dispersed in soil. Potassium-40 constitutes a significant part of elemental potassium which makes up 2.4 percent of the earth’s crust. Concentrations of minerals that collect in ash from the burning of coal for energy are sometimes quite high in radioactivity. The vast majority of ash from burning coal remains behind in the furnace, but the
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