 Samarium @-@ 149 has high cross @-@ section for neutron capture ( 41 @,@ 000 barns ) and is therefore used in the control rods of nuclear reactors . Its advantage compared to competing materials , such as boron and cadmium , is stability of absorption – most of the fusion and decay products of samarium @-@ 149 are other isotopes of samarium that are also good neutron absorbers . For example , the cross section of samarium @-@ 151 is 15 @,@ 000 barns , it is on the order of hundreds of barns for <unk> , 152Sm , and 153Sm , and is 6 @,@ 800 barns for natural ( mixed @-@ isotope ) samarium . Among the decay products in a nuclear reactor , samarium @-@ 149 is regarded as the second most important for the reactor design and operation after xenon @-@ 135 . 
