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.
The method of isochron dating is used to find the date at which a rock (or group of rocks) are formed.
[5] 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: 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).