Primordial Radionuclides

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Primordial radionuclides are left-over from when the world and the universe were created. They are typically long-lived, with half-lives often on the order of hundreds of millions of years. Radionuclides that exist for more than 30 half-lives are not measurable. The progeny or decay products of the long-lived radionuclides are also under this heading. Here is some basic information on some common primordial radionuclides:

Primordial nuclides
Nuclide          
Symbol
Half-life             
Natural Activity
Uranium 235
235U
7.04 x 108 a
0.72% of all natural uranium
Uranium 238
238U
4.47 x 109 a
99.2745% of all natural uranium; 0.5 to 4.7 ppm total uranium in the common rock types
Thorium 232
232Th
1.41 x 1010 a
1.6 to 20 ppm in the common rock types with a crustal average of 10.7 ppm
Radium 226
226Ra
1.60 x 103 a
0.42 pCi/g (16 Bq/kg) in limestone and 1.3 pCi/g (48 Bq/kg) in igneous rock
Radon 222
222Rn
3.82 days
Noble Gas; annual average outdoor air concentrations range in the US from 0.016 pCi/L (0.6 Bq/m3) to 0.75 pCi/L (28 Bq/m3)
Potassium 40
40K
1.28 x 109 a
Soil - 1-30 pCi/g (0.037-1.1 Bq/g)


Some nuclides like 232Th have several members in its decay chain. You can roughly follow the chain starting with 232Th:

[math]^{232}Th \rightarrow ^{228}Ac \rightarrow 224Ra \rightarrow 220Rn \rightarrow 216Po \rightarrow 212Pb \rightarrow 212Bi \rightarrow 212Po \rightarrow 208Pb(stable)[/math]

or starting with 238U:

[math]238U \rightarrow 234Th \rightarrow 234mPa \rightarrow 234U \rightarrow 230Th \rightarrow 226Ra \rightarrow 222Rn \rightarrow 218Po \rightarrow 210Pb \rightarrow 210Bi \rightarrow 210Po \rightarrow 206Pb(stable)[/math]

Some other primordial radionuclides are 50V, 87Rb, 113Cd, 115In, 123Te, 138La, 142Ce, 144Nd, 147Sm, 152Gd, 174Hf, 176Lu, 187Re, 190Pt, 192Pt, 209Bi.