146Sm
Samarium-146 (146Sm) is a radioactive isotope of the element samarium. It has a mass number of 146 and decays by alpha emission to 142Nd. The half-life is about 103 million years, placing its decay on timescales relevant to the early solar system rather than modern Earth.
Natural occurrence and production are limited. 146Sm is not produced or maintained in detectable amounts today
Applications and significance include its use in radiometric dating. The 146Sm-142Nd decay system provides a chronometer