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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 has a high cross section for neutron capture (41,000 barns) and so is used in control rods of nuclear reactors. Its advantage compared to competing materials, such as boron and cadmium, is stability of absorption – most of the fusion products of 149 Sm are other isotopes of samarium that are also good neutron absorbers.
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 .
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 ...
Conversely, of the 251 known stable nuclides, only five have both an odd number of protons and odd number of neutrons: hydrogen-2 , lithium-6, boron-10, nitrogen-14, and tantalum-180m. Also, only four naturally occurring, radioactive odd–odd nuclides have a half-life >10 9 years: potassium-40 , vanadium-50 , lanthanum-138 , and lutetium-176 .
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 ...
That is because α influences the rate of various nuclear reactions. For example, 149 Sm captures a neutron to become 150 Sm, and since the rate of neutron capture depends on the value of α, the ratio of the two samarium isotopes in samples from Oklo can be used to calculate the value of α from 2 billion years ago.
This page uses the meta infobox {{Infobox isotopes (meta)}} for the element isotopes infobox.. This infobox contains the table of § Main isotopes, and the § Standard atomic weight.