Naturally occurring samarium is composed of five stable isotopes, ¹⁴⁴Sm, ¹⁴⁹Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and two extremely long-lived radioisotopes, ¹⁴⁷Sm and ¹⁴⁸Sm, with ¹⁵²Sm being the most abundant. Wikipedia