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:
232Th
or starting with 238U:
Some other primordial radionuclides are 50V, 87Rb, 113Cd, 115In, 123Te, 138La, 142Ce, 144Nd, 147Sm, 152Gd, 174Hf, 176Lu, 187Re, 190Pt, 192Pt, 209Bi.