149Sm

149Sm is a stable isotope of the lanthanide element samarium (atomic number 62) with a mass number of 149. It is one of the naturally occurring isotopes of samarium and constitutes a notable fraction of natural samarium in minerals such as bastnasite and monazite.

Nuclear properties of 149Sm include its stability and very large cross-section for thermal neutron capture. While it does not decay radioactively, it readily absorbs neutrons, a property that makes it an important neutron absorber in nuclear systems. The thermal neutron capture cross-section of 149Sm is on the order of tens of thousands of barns. When it captures a neutron, it forms 150Sm.

Occurrence and production of 149Sm arise largely from natural samarium, where it exists as one of the stable isotopes. In nuclear reactors, 149Sm can be produced from neutron capture on 148Sm and contributes to the neutron-absorption balance in the fuel and coolant. Its high neutron capture cross-section means that even small quantities can significantly affect reactor reactivity over time.

Applications and significance of 149Sm include its use as a burnable neutron absorber in certain nuclear fuel designs and materials. Because of its strong neutron absorption, it is carefully accounted for in reactor physics calculations and fuel management. Chemically, 149Sm behaves like other samarium isotopes and forms similar compounds, requiring standard safety handling for rare-earth elements.