| Abstrakt: |
Actinide elements are ubiquitous in nature. Uranium and thorium are present in the Earth΄s crust with average concentrations of 1–10 μg g-1, making them more abundant than Ag, Sb, Cd, or Hg. While U and Th can even be found as major or minor mineral constituents in a variety of geochemical environments, typically they are highly dispersed and present only at trace or ultra–trace concentrations in most natural materials. Because 238U, 235U, and 232Th are the parents of the three naturally occurring non–extinct radioactive decay chains, they are always accompanied by lower concentrations of their radioactive progeny, many of which are also actinides (Table 30.1). [ABSTRACT FROM AUTHOR] |
