[7][8] 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 equilibrium concentration (and thus the poisoning effect) builds to an equilibrium value in about 500 hours (about 20 days) of reactor operation, and since 149Sm is stable, the concentration remains essentially constant during further reactor operation.
This contrasts with xenon-135, which accumulates from the beta decay of iodine-135 (a short lived fission product) and has a high neutron cross section, but itself decays with a half-life of 9.2 hours (so does not remain in constant concentration long after the reactor shutdown), causing the so-called xenon pit.
Since the ratios between the production and absorption rates of 151Sm and 149Sm are almost equal, the two isotopes should reach similar equilibrium concentrations.
[14] It is treated by the body in a similar manner to calcium, and it localizes selectively to bone.