Samarium-147 (147Sm or Sm-147) is an isotope of samarium, making up 15% of natural samarium. It is an extremely long-lived radioisotope, with a half-life of 1.06×1011 years, although measurements have ranged from 1.05×1011 to 1.17×1011 years.[1][2] It is mainly used in radiometric dating.[3]
| General | |
|---|---|
| Symbol | 147Sm |
| Names | Samarium-147, 147Sm, Sm-147 |
| Protons (Z) | 62 |
| Neutrons (N) | 85 |
| Nuclide data | |
| Natural abundance | 15.00% |
| Half-life (t1/2) | 1.06×1011 years |
| Isotope mass | 146.9148979(26) Da |
| Spin | 7/2− |
| Parent isotopes | 147Pm (β−) 151Gd (α) |
| Decay products | 143Nd |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| Isotopes of samarium Complete table of nuclides | |
Uses
editSamarium-147 is used in samarium–neodymium dating. The method of isochron dating is used to find the date at which a rock (or group of rocks) are formed.[4] The Sm-Nd isochron plots the ratio of radiogenic 143Nd to non-radiogenic 144Nd against the ratio of the parent isotope 147Sm to the non-radiogenic isotope 144Nd. 144Nd is used to normalize the radiogenic isotope in the isochron because it is a slightly radioactive and relatively abundant neodymium isotope.
The Sm-Nd isochron is defined by the following equation:
where:
- t is the age of the sample,
- λ is the decay constant of 147Sm,
- (eλt−1) is the slope of the isochron which defines the age of the system.
Alternatively, one can assume that the material formed from mantle material which was following the same path of evolution of these ratios as chondrites, and then again the time of formation can be calculated (see Samarium–neodymium dating#The CHUR model).[4][5]
See also
editReferences
edit- ^ Wright, P. M.; Steinberg, E. P.; Glendenin, L. E. (1961-07-01). "Half-Life of Samarium-147". Physical Review. 123 (1): 205–208. Bibcode:1961PhRv..123..205W. doi:10.1103/PhysRev.123.205.
- ^ Kinoshita, Norikazu; Yokoyama, Akihiko; Nakanishi, Takashi (2003). "Half-Life of Samarium-147". Journal of Nuclear and Radiochemical Sciences. 4 (1): 5–7. doi:10.14494/jnrs2000.4.5. S2CID 120606011.
- ^ Currie, Lloyd A., ed. (1982-01-29). Nuclear and Chemical Dating Techniques: Interpreting the Environmental Record. ACS Symposium Series. Vol. 176. WASHINGTON, D. C.: AMERICAN CHEMICAL SOCIETY. doi:10.1021/bk-1982-0176.ch001. ISBN 978-0-8412-0669-4.
- ^ a b Depaolo, D. J.; Wasserburg, G. J. (1976). "Nd isotopic variations and petrogenetic models" (PDF). Geophysical Research Letters. 3 (5): 249. Bibcode:1976GeoRL...3..249D. doi:10.1029/GL003i005p00249.
- ^ McCulloch, M. T.; Wasserburg, G. J. (1978). "Sm-Nd and Rb-Sr Chronology of Continental Crust Formation". Science. 200 (4345): 1003–11. Bibcode:1978Sci...200.1003M. doi:10.1126/science.200.4345.1003. PMID 17740673. S2CID 40675318.