Samarium-147

Naturally occurring samarium (Sm) is composed of five stable isotopes, ¹⁴⁴Sm, ¹⁴⁹Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and two extremely long-lived radioisotopes, ¹⁴⁷Sm (half life: 1.06×10¹¹ y) and ¹⁴⁸Sm (7×10¹⁵ y), with ¹⁵²Sm being the most abundant (26.75% natural abundance). ¹⁴⁶Sm is also fairly long-lived (6.8×10⁷ y), but is not long-lived enough to have survived from the formation of the Solar System on Earth, although it remains useful in radiometric dating in the Solar System.

Other than the naturally occurring isotopes, the longest-lived radioisotopes are ¹⁵¹Sm, which has a half-life of 88.8 years, and ¹⁴⁵Sm, which has a half-life of 340 days. All of the remaining radioisotopes have half-lives that are less than two days, and the majority of these have half-lives that are less than 48 seconds. This element also has twelve known isomers with the most stable being ^141mSm (t_1/2 22.6 minutes), ^143m1Sm (t_1/2 66 seconds) and ^139mSm (t_1/2 10.7 seconds).

The long lived isotopes,¹⁴⁶Sm, ¹⁴⁷Sm, and ¹⁴⁸Sm primarily decay by alpha decay to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones decay by beta decay to isotopes of europium.

Isotopes of samarium are used in samarium-neodymium dating for determining the age relationships of rocks and meteorites.

¹⁵¹Sm is a medium-lived fission product and acts as a neutron poison in the nuclear fuel cycle. The stable fission product ¹⁴⁹Sm is also a neutron poison.

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