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The stable fission product 149 Sm is also a neutron poison. Samarium is theoretically the lightest element with even atomic number with no stable isotopes (all isotopes of it can theoretically go either alpha decay or beta decay or double beta decay), other such elements are those with atomic numbers > 66 (dysprosium, which is the heaviest ...
Samarium-149 is an observationally stable isotope of samarium (predicted to decay, but no decays have ever been observed, giving it a half-life at least several orders of magnitude longer than the age of the universe), and a product of the decay chain from the fission product 149 Nd (yield 1.0888%).
Examples include carbon-14, nitrogen-15, and oxygen-16 in the table above. Isobars are nuclides with the same number of nucleons (i.e. mass number) but different numbers of protons and neutrons. Isobars neighbor each other diagonally from lower-left to upper-right. Examples include carbon-14, nitrogen-14, and oxygen-14 in the table above.
There are 6 stable nuclides and one radioactive primordial nuclide with neutron number 82 (82 is the neutron number with the most stable nuclides, since it is a magic number): barium-138, lanthanum-139, cerium-140, praseodymium-141, neodymium-142, and samarium-144, as well as the radioactive primordial nuclide xenon-136, which decays by a very ...
Samarium has seven naturally occurring isotopes, and neodymium has seven. The two elements are joined in a parent–daughter relationship by the alpha decay of parent 147 Sm to radiogenic daughter 143 Nd with a half-life of 1.066(5) × 10 11 years and by the alpha decay of 146 Sm (an almost-extinct radionuclide with a half-life of 9.20(26) × 10 7 years [2] [a]) to produce 142 Nd.
Some fission products decay with the release of delayed neutrons, important to nuclear reactor control. Other fission products, such as xenon-135 and samarium-149, have a high neutron absorption cross section. Since a nuclear reactor must balance neutron production and absorption rates, fission products that absorb neutrons tend to "poison" or ...
Some of the fission products generated during nuclear reactions have a high neutron absorption capacity, such as xenon-135 (microscopic cross-section σ = 2,000,000 barns (b); up to 3 million barns in reactor conditions) [3] and samarium-149 (σ = 74,500 b). Because these two fission product poisons remove neutrons from the reactor, they will ...
Samarium-149 is the second most important neutron poison in nuclear reactor physics. Samarium-151, produced at lower yields, is the third most abundant medium-lived fission product but emits only weak beta radiation. Both have high neutron absorption cross sections, so that much of them produced in a reactor are later destroyed there by neutron ...