Samarium-147 Explained

Samarium-147
Mass Number:147
Symbol:Sm
Num Neutrons:85
Num Protons:62
Abundance:15.00%
Halflife:1.06 years
Decay Product:Neodymium-143
Decay Mass:143
Decay Symbol:Nd
Parent:Promethium-147
Parent Mass:147
Parent Symbol:Pm
Parent Decay:β-
Parent2:Gadolinium-151
Parent2 Mass:151
Parent2 Symbol:Gd
Parent2 Decay:α
Mass:146.9148979(26)
Spin:7/2−
Decay Mode1:Alpha

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 this can range from 1.05×1011[1] to 1.17×1011[2] years. It is mainly used in radiometric dating.[3]

Uses

See main article: article and Samarium–neodymium dating.

Samarium-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:

\left({
143

Nd

}\right)_ = \left(\frac\right)_ + \left(\frac\right) \cdot (e^-1),

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).[5]

See also

Notes and References

  1. Wright . P. M. . Steinberg . E. P. . Glendenin . L. E. . 1961-07-01 . Half-Life of Samarium-147 . Physical Review . 123 . 1 . 205–208 . 10.1103/PhysRev.123.205. 1961PhRv..123..205W .
  2. Kinoshita . Norikazu . Yokoyama . Akihiko . Nakanishi . Takashi . 2003 . Half-Life of Samarium-147 . Journal of Nuclear and Radiochemical Sciences . 4 . 1 . 5–7 . 10.14494/jnrs2000.4.5. 120606011 . free .
  3. Book: Nuclear and Chemical Dating Techniques: Interpreting the Environmental Record . 1982-01-29 . AMERICAN CHEMICAL SOCIETY . 978-0-8412-0669-4 . Currie . Lloyd A. . ACS Symposium Series . 176 . WASHINGTON, D. C. . en . 10.1021/bk-1982-0176.ch001.
  4. Depaolo. D. J.. Wasserburg. G. J.. Nd isotopic variations and petrogenetic models. Geophysical Research Letters. 3. 249. 1976. 10.1029/GL003i005p00249. 1976GeoRL...3..249D. 5.
  5. McCulloch. M. T.. Wasserburg. G. J.. Sm-Nd and Rb-Sr Chronology of Continental Crust Formation. Science. 200. 1003–11. 1978. 10.1126/science.200.4345.1003. 4345. 17740673. 1978Sci...200.1003M . 40675318.