Naturally occurring hazardous radionuclides

Radioactive decay usually does not immediately lead to a stable end product, but to other unstable nuclei that form a decay series (Kiefer 1990). The most important examples of unstable nuclei are started by very heavy, naturally occurring nuclei. Because the mass number changes only with a decay, all members of a series can be classified according to their mass numbers (see the uranium-238 decay series in Figure 32.2). A total of three natural decay series — formed at the birth of our planet — are named after their parent isotope Th, and (Figure 32.3). Several shorter decay series also exist. For example, Sr decays with a Tb 1/2 of 28 years by [3 emission to °Y, which in turn disintegrates (P emission) with a Tb 1/2 of 64 h to the stable °Zr (Kiefer 1990). Other examples of known radionuclides since the Earth s origin include " °K and Rb. In hazard assessments, all members of a decay series must be considered. 

Most uranium and thorium mill tailings that contain elevated levels of naturally occurring radionuclides could be classified as low-hazard waste, but only under conditions of perpetual... 

Radioactive substances (radionuclides) are known health hazards that emit energetic waves and/or particles that can cause both carcinogenic and noncarcinogenic health effects. Radionuclides pose unique threats to source water supplies and chemical processing, storage, or distribution systems because radiation emitted from radionuclides in chemical or industrial waste systems can affect individuals through several pathways by direct contact with, ingestion or inhalation of, or external exposure to, the contaminated waste stream. While radiation can occur naturally in some cases due to the decay of some minerals, intentional and nonintentional releases of... 

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