Samarium-146

Samarium (Sm) is a chemical element with atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Naturally occurring samarium has a radioactivity of 128 Bq/g. It is composed of four stable isotopes: 144Sm, 150Sm, 152Sm and 154Sm, and three extremely long-lived radioisotopes, 147Sm (half-life t½ = 1.06×1011 years), 148Sm (7×1015 years) and 149Sm (>2×1015 years), with 152Sm being the most abundant (natural abundance 26.75%).

Similarly, Samarium 146 is a long lived isoptope of Samarium. This isotope emits an alpha particle and changes the atom into a different element. This was recently making news as it has been used as chart out the life of solar system. Please note that isotopes of samarium are used in samarium-neodymium dating for determining the age relationships of rocks and meteorites.