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Radiogenic



A radiogenic nuclide is one that is produced by a process of radioactive decay.

Additional recommended knowledge

Lead is perhaps the best example of a radiogenic substance, as it is produced from the radioactive decay of uranium and thorium. Specifically, Pb-206 is formed from U-238, Pb-207 from U-235, and Pb-208 from Th-232. Other substances considered radiogenic are argon-40, formed from radioactive potassium, and nitrogen-14, which is formed by the decay of carbon-14. U-238, U-235, and Th-232 themselves are likely to be radiogenic as well, being formed from the decay of those nuclei of the elements heavier than uranium which do not undergo spontaneous fission, just after they were formed in stellar supernovae. Other important examples of radiogenic elements are radon and helium, both of which form during the decay of heavier elements in bedrock. The global supply of helium is radiogenic.

Radiogenic nuclides (more commonly referred to as 'radiogenic isotopes') form some of the most important tools in Geology. They are used in two principal ways:

1) In comparison with the quantity of the radioactive 'parent isotope' in a system, the quantity of the radiogenic 'daughter product' is used as a radiometric dating tool (e.g. uranium-lead geochronology).

2) In comparison with the quantity of a non-radiogenic isotope of the same element, the quantity of the radiogenic isotope is used as an isotopic tracer (e.g. 206Pb/204Pb). This technique is discussed in more detail under the heading isotope geochemistry.

The following table lists some of the most important radiogenic isotope systems used in Geology, in order of decreasing half-life of the radioactive parent isotope. The values given for half-life and decay constant are the current consensus values in the Isotope Geology community.[1] Extinct nuclides are not presently included. **indicates ultimate decay product of a series.

Parent nuclide Product nuclide Decay constant (yr-1) Half-life
190Pt 186Os 1.477 ×10-12 469.3 Byr
147Sm 143Nd 6.54 ×10-12 106 Byr
87Rb 87Sr 1.402 ×10-11 49.44 Byr
187Re 187Os 1.666 ×10-11 41.6 Byr
176Lu 176Hf 1.867 ×10-11 37.1 Byr
232Th 208Pb** 4.9475 ×10-11 14.01 Byr
40K 40Ar 5.81 ×10-11 11.93 Byr
238U 206Pb** 1.55125 ×10-10 4.468 Byr
40K 40Ca 4.962 ×10-10 1.397 Byr
235U 207Pb** 9.8485 ×10-10 0.7038 Byr
129I 129Xe 4.3 ×10-8 16 Myr
10Be 10B 4.6 ×10-7 1.5 Myr
26Al 26Mg 9.9 ×10-7 0.7 Myr
36Cl 36Ar/S 2.24 ×10-6 310 kyr
234U 230Th 2.826 ×10-6 245.25 kyr
230Th 226Ra 9.1577 ×10-6 75.69 kyr
231Pa 227Ac 2.116 ×10-5 32.76 kyr
14C 14N 1.2097 ×10-4 5730 yr
226Ra 222Rn 4.33 ×10-4 1600 yr

References

  1. ^ Dickin, A. P., 2005. Radiogenic Isotope Geology, Cambridge University Press.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radiogenic". A list of authors is available in Wikipedia.
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