Natural and Artificial Radioelements

Radioelements are elements existing only in the form of radionuclides, but not as stable isotopes, as already mentioned in section 2.1. 

The natural radioelements are listed in Table 14.1. Isotopes of these elements are members of the uranium, actinium and thorium families (Table 1.2, and Tables 4.1 to 4.3). In the ores of U and Th the concentrations of natural radioelements are relatively high and proportional to the half-life. The average concentration of U in the earth s crust is about 2.9 mg/kg (ppm) and that of Th about 11 mg/kg (ppm). The 

Atomic number Z Name of the element (Symbol) Longest-lived nuclide (Half-life) Discovery Remarks 

85 Astatine (At) 210At (8.3 h) 1940 Corson, McKenzie and Segre Halogen volatile 

88 Radium (Ra) 226 Ra (1600y) 1898 P. and M. Curie Alkaline-earth metal similar to Ba 

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