Greetings class! Today we start out our series in "better know a 'tope" with the stable nuclide 143Nd. Neodymium has atomic number 60 and has gotten a lot of attention in recent years as a key component in powerful magnets and previously in use in lasers. One of the most common solid state lasers is the neodymium-yttrium aluminum garnet or Nd:YAG laser. Neodymium magnets are among the most powerful magnets known and are used in things such as motors (in hybrid cars) and in wind turbines to generate electricity.
The stable isotope 143Nd is the daughter product by alpha decay of 147Sm; this is the basis for Sm-Nd geochronology. The decay of 147Sm to 143Nd has a half life of ~106 billion years. This makes the system potentially useful for dating minerals across a wide range of ages back to earth formation. Sm-Nd geochronology has many challenges including the relatively low concentrations of rare earths in many minerals, low parent-daughter ratios, and (similar to many systems) potential parent daughter fractionation after the growth of the mineral. Despite these challenges, Sm-Nd geochronology lends itself quite well to a few minerals, in particular the dating of garnets. Garnets tend to have very high Sm/Nd ratios compared to most other crustal minerals, leading to well constrained isochrons.
In addition to mineral specific geochronology, 143Nd is very important in determining Nd-model ages and mantle evolution over time. In samples that are well constrained, knowing the current 143/144Nd ratio as well as the Sm/Nd ratio and the age, an initial 143/144Nd ratio can be calculated. Based on the age and the initial ratio calculated, information can be derived relating to when the original magma from which that rock is derived was segregated from the mantle because Sm and Nd have slightly different compatibilities.
For further reading on neodymium and some applications to garnet geochronology see
DePaolo, D.J., 1988. Neodymium isotope geochemistry; an introduction. Minerals and Rocks, 20. Springer-Verlag, Berlin-Heidelberg, Federal Republic of Germany (DEU), 187 pp.
Pollington, A.D., Baxter, E.F., 2010. High resolution Sm-Nd garnet geochronology reveals the uneven pace of tectonometamorphic processes. Earth and Planetary Science Letters, 293(1-2): 63-71.
Pollington, A.D., Baxter, E.F., 2011. High precision microsampling and preparation of zoned garnet porphyroblasts for Sm-Nd geochronology. Chemical Geology, 281(3-4): 270-282.
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