Naturally occurring

samarium Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of s ...

(₆₂Sm) is composed of five stable

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

s, ¹⁴⁴Sm, ¹⁴⁹Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and two extremely long-lived

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

s, ¹⁴⁷Sm (half life: 1.066 y) and ¹⁴⁸Sm (6.3 y), with ¹⁵²Sm being the most abundant (26.75%

natural abundance In physics, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the ato ...

). ¹⁴⁶Sm (9.20 y) is also fairly long-lived, but is not long-lived enough to have survived in significant quantities from the formation of the Solar System on Earth, although it remains useful in radiometric dating in the Solar System as an

extinct radionuclide An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, but has since decayed to virtually zero abundance and is no longer detectable as a primordial nu ...

. It is the longest-lived nuclide that has not yet been confirmed to be primordial. Its instability is due to having 84 neutrons (two more than 82, which is a magic number corresponding to a stable neutron configuration), and so it may emit an

alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...

(which has 2 neutrons) to form neodymium-142 with 82 neutrons. Other than the naturally occurring isotopes, the longest-lived radioisotopes are ¹⁵¹Sm, which has a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of 94.6 years, and ¹⁴⁵Sm, which has a half-life of 340 days. All of the remaining radioisotopes, which range from ¹²⁹Sm to ¹⁶⁸Sm, have half-lives that are less than two days, and the majority of these have half-lives that are less than 48 seconds. This element also has twelve known

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the existence or possibili ...

with the most stable being ^141mSm (t_1/2 22.6 minutes), ^143m1Sm (t_1/2 66 seconds) and ^139mSm (t_1/2 10.7 seconds). The long lived isotopes, ¹⁴⁶Sm, ¹⁴⁷Sm, and ¹⁴⁸Sm, primarily decay by

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an a ...

isotopes of neodymium Naturally occurring neodymium (60Nd) is composed of five stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and two long-lived radioisotopes, 144Nd and 150Nd. In all, 35 radioisotop ...

. Lighter unstable isotopes of samarium primarily decay by

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

isotopes of promethium Promethium (61Pm) is an artificial element, except in trace quantities as a product of spontaneous fission of 238U and 235U and alpha decay of 151Eu, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no s ...

, while heavier ones decay by

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

isotopes of europium Naturally occurring europium (63Eu) is composed of two isotopes, 151Eu and 153Eu, with 153Eu being the most abundant (52.2% natural abundance). While 153Eu is observationally stable (theoretically can undergo alpha decay with half-life over 5.5×1 ...

. A 2012 paper revising the estimated half-life of ¹⁴⁶Sm from 10.3(5)×10⁷ y to 6.8(7)×10⁷ y was retracted in 2023. Isotopes of samarium are used in

samarium–neodymium dating Samarium–neodymium dating is a radiometric dating method useful for determining the ages of rocks and meteorites, based on the alpha decay of the long-lived samarium isotope () to the stable radiogenic neodymium isotope (). Neodymium isotope ra ...

for determining the age relationships of rocks and meteorites. ¹⁵¹Sm is a

medium-lived fission product Long-lived fission products (LLFPs) are radioactive materials with a long half-life (more than 200,000 years) produced by nuclear fission of uranium and plutonium. Because of their persistent Ionizing radiation, radiotoxicity, it is necessary to is ...

and acts as a

neutron poison In applications such as nuclear reactors, a neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section. In such applications, absorbing neutrons is normally an undesirable ef ...

in the

nuclear fuel cycle The nuclear fuel cycle, also known as the nuclear fuel chain, describes the series of stages that nuclear fuel undergoes during its production, use, and recycling or disposal. It consists of steps in the ''front end'', which are the preparation o ...

. The stable

fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the releas ...

¹⁴⁹Sm is also a neutron poison. Samarium is theoretically the lightest element with even

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (''n''p) or the number of pro ...

with no stable isotopes (all isotopes of it can theoretically go either

double beta decay In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa, inside an atomic nucleus. As in single beta decay, this process allows the atom to move cl ...

), other such elements are those with atomic numbers > 66 (

dysprosium Dysprosium is a chemical element; it has symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it ...

, which is the heaviest theoretically stable nuclide).

List of isotopes

, -id=Samarium-129 , rowspan=2, ¹²⁹Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 67 , rowspan=2, 128.95456(54)# , rowspan=2, 550(100) ms , β⁺ (?%) , ¹²⁹Pm , rowspan=2, (1/2+,3/2+) , rowspan=2, , rowspan=2, , - , β⁺, p (?%) , ¹²⁸Nd , -id=Samarium-130 , ¹³⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 68 , 129.94879(43)# , 1# s , , , 0+ , , , -id=Samarium-131 , rowspan=2, ¹³¹Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 69 , rowspan=2, 130.94602(43)# , rowspan=2, 1.2(2) s , β⁺ , ¹³¹Pm , rowspan=2, 5/2+# , rowspan=2, , rowspan=2, , - , β⁺, p (?%) , ¹³⁰Nd , -id=Samarium-132 , ¹³²Sm , style="text-align:right" , 62 , style="text-align:right" , 70 , 131.94081(32)# , 4.0(3) s , β⁺ , ¹³²Pm , 0+ , , , -id=Samarium-133 , rowspan=2, ¹³³Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 71 , rowspan=2, 132.93856(32)# , rowspan=2, 2.89(16) s , β⁺ (?%) , ¹³³Pm , rowspan=2, (5/2+) , rowspan=2, , rowspan=2, , - , β⁺, p (?%) , ¹³²Nd , -id=Samarium-133m , style="text-indent:1em" , ^133mSm , colspan="3" style="text-indent:2em" , 120(60)# keV , 3.5(4) s , β⁺ , ¹³³Pm , (1/2−) , , , -id=Samarium-134 , ¹³⁴Sm , style="text-align:right" , 62 , style="text-align:right" , 72 , 133.93411(21)# , 9.5(8) s , β⁺ , ¹³⁴Pm , 0+ , , , -id=Samarium-135 , rowspan=2, ¹³⁵Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 73 , rowspan=2, 134.93252(17) , rowspan=2, 10.3(5) s , β⁺ (99.98%) , ¹³⁵Pm , rowspan=2, (7/2+) , rowspan=2, , rowspan=2, , - , β⁺, p (0.02%) , ¹³⁴Nd , -id=Samarium-136 , ¹³⁶Sm , style="text-align:right" , 62 , style="text-align:right" , 74 , 135.928276(13) , 47(2) s , β⁺ , ¹³⁶Pm , 0+ , , , -id=Samarium-136m , style="text-indent:1em" , ^136mSm , colspan="3" style="text-indent:2em" , 2264.7(11) keV , 15(1) μs , IT , ¹³⁶Sm , (8−) , , , -id=Samarium-137 , ¹³⁷Sm , style="text-align:right" , 62 , style="text-align:right" , 75 , 136.927008(31) , 45(1) s , β⁺ , ¹³⁷Pm , (9/2−) , , , -id=Samarium-138 , ¹³⁸Sm , style="text-align:right" , 62 , style="text-align:right" , 76 , 137.923244(13) , 3.1(2) min , β⁺ , ¹³⁸Pm , 0+ , , , -id=Samarium-139 , ¹³⁹Sm , style="text-align:right" , 62 , style="text-align:right" , 77 , 138.922297(12) , 2.57(10) min , β⁺ , ¹³⁹Pm , 1/2+ , , , -id=Samarium-139m , rowspan=2 style="text-indent:1em" , ^139mSm , rowspan=2 colspan="3" style="text-indent:2em" , 457.38(23) keV , rowspan=2, 10.7(6) s , IT (93.7%) , ¹³⁹Sm , rowspan=2, 11/2− , rowspan=2, , rowspan=2, , - , β⁺ (6.3%) , ¹³⁹Pm , -id=Samarium-140 , ¹⁴⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 78 , 139.918995(13) , 14.82(12) min , β⁺ , ¹⁴⁰Pm , 0+ , , , -id=Samarium-141 , ¹⁴¹Sm , style="text-align:right" , 62 , style="text-align:right" , 79 , 140.9184815(92) , 10.2(2) min , β⁺ , ¹⁴¹Pm , 1/2+ , , , -id=Samarium-141m , rowspan=2 style="text-indent:1em" , ^141mSm , rowspan=2 colspan="3" style="text-indent:2em" , 175.9(3) keV , rowspan=2, 22.6(2) min , β⁺ (99.69%) , ¹⁴¹Pm , rowspan=2, 11/2− , rowspan=2, , rowspan=2, , - , IT (0.31%) , ¹⁴¹Sm , -id=Samarium-142 , rowspan=2, ¹⁴²Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 80 , rowspan=2, 141.9152094(20) , rowspan=2, 72.49(5) min , EC (>95%) , rowspan=2, ¹⁴²Pm , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺ (<5%) , -id=Samarium-142m1 , style="text-indent:1em" , ^142m1Sm , colspan="3" style="text-indent:2em" , 2372.1(4) keV , 170(2) ns , IT , ¹⁴²Sm , 7− , , , -id=Samarium-142m2 , style="text-indent:1em" , ^142m2Sm , colspan="3" style="text-indent:2em" , 3662.2(7) keV , 480(60) ns , IT , ¹⁴²Sm , 10+ , , , -id=Samarium-143 , rowspan=2, ¹⁴³Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 81 , rowspan=2, 142.9146348(30) , rowspan=2, 8.75(6) min , EC (60.0%) , ¹⁴³Pm , rowspan=2, 3/2+ , rowspan=2, , rowspan=2, , - , β⁺ (40.0%) , ¹⁴³Pm , -id=Samarium-143m1 , rowspan=2 style="text-indent:1em" , ^143m1Sm , rowspan=2 colspan="3" style="text-indent:2em" , 753.99(16) keV , rowspan=2, 66(2) s , IT (99.76%) , ¹⁴³Sm , rowspan=2, 11/2− , rowspan=2, , rowspan=2, , - , β⁺ (0.24%) , ¹⁴³Pm , -id=Samarium-143m2 , style="text-indent:1em" , ^143m2Sm , colspan="3" style="text-indent:2em" , 2793.8(13) keV , 30(3) ms , IT , ¹⁴³Sm , 23/2− , , , -id=Samarium-144 , ¹⁴⁴Sm , style="text-align:right" , 62 , style="text-align:right" , 82 , 143.9120063(16) , colspan=3 align=center,

Observationally stable Stable nuclides are isotopes of a chemical element whose nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The nuclei of such isotopes are not radioactive and unlike radionuc ...

, 0+ , 0.0308(4) , , -id=Samarium-144m , style="text-indent:1em" , ^144mSm , colspan="3" style="text-indent:2em" , 2323.60(8) keV , 880(25) ns , IT , ¹⁴⁴Sm , 6+ , , , -id=Samarium-145 , ¹⁴⁵Sm , style="text-align:right" , 62 , style="text-align:right" , 83 , 144.9134172(16) , 340(3) d , EC , ¹⁴⁵Pm , 7/2− , , , -id=Samarium-145m , style="text-indent:1em" , ^145mSm , colspan="3" style="text-indent:2em" , 8815(1) keV , 3.52(16) μs , IT , ¹⁴⁵Sm , 49/2+ , , , -id=Samarium-146 , ¹⁴⁶Sm , style="text-align:right" , 62 , style="text-align:right" , 84 , 145.9130468(33) , 9.20(26) y , α , ¹⁴²Nd , 0+ , Trace , , - , ¹⁴⁷Sm Primordial

Fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the releas ...

Used in

Samarium–neodymium dating Samarium–neodymium dating is a radiometric dating method useful for determining the ages of rocks and meteorites, based on the alpha decay of the long-lived samarium isotope () to the stable radiogenic neodymium isotope (). Neodymium isotope ra ...

, style="text-align:right" , 62 , style="text-align:right" , 85 , 146.9149044(14) , 1.066(5) y , α , ¹⁴³Nd , 7/2− , 0.1500(14) , , -id=Samarium-148 , ¹⁴⁸Sm , style="text-align:right" , 62 , style="text-align:right" , 86 , 147.9148292(13) , 6.3(13) y , α , ''¹⁴⁴Nd'' , 0+ , 0.1125(9) , , - , ¹⁴⁹Sm

Neutron poison In applications such as nuclear reactors, a neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section. In such applications, absorbing neutrons is normally an undesirable ef ...

in reactors , style="text-align:right" , 62 , style="text-align:right" , 87 , 148.9171912(12) , colspan=3 align=center, Observationally stable , 7/2− , 0.1382(10) , , -id=Samarium-150 , ¹⁵⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 88 , 149.9172820(12) , colspan=3 align=center, Observationally stable , 0+ , 0.0737(9) , , - , ¹⁵¹Sm , style="text-align:right" , 62 , style="text-align:right" , 89 , 150.9199389(12) , 94.6(6) y , β⁻ , ''¹⁵¹Eu'' , 5/2− , , , -id=Samarium-151m , style="text-indent:1em" , ^151mSm , colspan="3" style="text-indent:2em" , 261.13(4) keV , 1.4(1) μs , IT , ¹⁵¹Sm , (11/2)− , , , -id=Samarium-152 , ¹⁵²Sm , style="text-align:right" , 62 , style="text-align:right" , 90 , 151.9197386(11) , colspan=3 align=center, Observationally stable , 0+ , 0.2674(9) , , - , ¹⁵³Sm , style="text-align:right" , 62 , style="text-align:right" , 91 , 152.9221036(11) , 46.2846(23) h , β⁻ , ¹⁵³Eu , 3/2+ , , , -id=Samarium-153m , style="text-indent:1em" , ^153mSm , colspan="3" style="text-indent:2em" , 98.39(10) keV , 10.6(3) ms , IT , ¹⁵³Sm , 11/2− , , , -id=Samarium-154 , ¹⁵⁴Sm , style="text-align:right" , 62 , style="text-align:right" , 92 , 153.9222158(14) , colspan=3 align=center, Observationally stable , 0+ , 0.2274(14) , , -id=Samarium-155 , ¹⁵⁵Sm , style="text-align:right" , 62 , style="text-align:right" , 93 , 154.9246466(14) , 22.18(6) min , β⁻ , ¹⁵⁵Eu , 3/2− , , , -id=Samarium-155m1 , style="text-indent:1em" , ^155m1Sm , colspan="3" style="text-indent:2em" , 16.5467(19) keV , 2.8(5) μs , IT , ¹⁵⁵Sm , 5/2+ , , , -id=Samarium-155m2 , style="text-indent:1em" , ^155m2Sm , colspan="3" style="text-indent:2em" , 538.03(19) keV , 1.00(8) μs , IT , ¹⁵⁵Sm , 11/2− , , , -id=Samarium-156 , ¹⁵⁶Sm , style="text-align:right" , 62 , style="text-align:right" , 94 , 155.9255382(91) , 9.4(2) h , β⁻ , ¹⁵⁶Eu , 0+ , , , -id=Samarium-156m , style="text-indent:1em" , ^156mSm , colspan="3" style="text-indent:2em" , 1397.55(9) keV , 185(7) ns , IT , ¹⁵⁶Sm , 5− , , , -id=Samarium-157 , ¹⁵⁷Sm , style="text-align:right" , 62 , style="text-align:right" , 95 , 156.9284186(48) , 8.03(7) min , β⁻ , ¹⁵⁷Eu , 3/2−# , , , -id=Samarium-158 , ¹⁵⁸Sm , style="text-align:right" , 62 , style="text-align:right" , 96 , 157.9299493(51) , 5.30(3) min , β⁻ , ¹⁵⁸Eu , 0+ , , , -id=Samarium-159 , ¹⁵⁹Sm , style="text-align:right" , 62 , style="text-align:right" , 97 , 158.9332171(64) , 11.37(15) s , β⁻ , ¹⁵⁹Eu , 5/2− , , , -id=Samarium-159m , style="text-indent:1em" , ^159mSm , colspan="3" style="text-indent:2em" , 1276.5(8) keV , 116(8) ns , IT , ¹⁵⁹Sm , (15/2+) , , , -id=Samarium-160 , ¹⁶⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 98 , 159.9353370(21) , 9.6(3) s , β⁻ , ¹⁶⁰Eu , 0+ , , , -id=Samarium-160m1 , style="text-indent:1em" , ^160m1Sm , colspan="3" style="text-indent:2em" , 1361.3(4) keV , 120(46) ns , IT , ¹⁶⁰Sm , (5−) , , , -id=Samarium-160m2 , style="text-indent:1em" , ^160m2Sm , colspan="3" style="text-indent:2em" , 2757.3(4) keV , 1.8(4) μs , IT , ¹⁶⁰Sm , (11+) , , , -id=Samarium-161 , ¹⁶¹Sm , style="text-align:right" , 62 , style="text-align:right" , 99 , 160.9391601(73) , , β⁻ , ¹⁶¹Eu , 7/2+# , , , -id=Samarium-161m , style="text-indent:1em" , ^161mSm , colspan="3" style="text-indent:2em" , 1388.1(6) keV , 2.6(4) μs , IT , ¹⁶¹Sm , (17/2−) , , , -id=Samarium-162 , ¹⁶²Sm , style="text-align:right" , 62 , style="text-align:right" , 100 , 161.9416217(38) , , β⁻ , ¹⁶²Eu , 0+ , , , -id=Samarium-162m , style="text-indent:1em" , ^162mSm , colspan="3" style="text-indent:2em" , 1009.4(5) keV , 1.78(7) μs , IT , ¹⁶²Sm , (4−) , , , -id=Samarium-163 , rowspan=2, ¹⁶³Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 101 , rowspan=2, 162.9456791(79) , rowspan=2, , β⁻ , ¹⁶³Eu , rowspan=2, 1/2−# , rowspan=2, , rowspan=2, , - , β⁻, n (<0.1%) , ¹⁶²Eu , -id=Samarium-164 , rowspan=2, ¹⁶⁴Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 102 , rowspan=2, 163.9485501(44) , rowspan=2, , β⁻ , ¹⁶⁴Eu , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (<0.7%) , ¹⁶³Eu , -id=Samarium-164m , style="text-indent:1em" , ^164mSm , colspan="3" style="text-indent:2em" , 1485.5(12) keV , 600(140) ns , IT , ¹⁶⁴Sm , (6−) , , , -id=Samarium-165 , rowspan=2, ¹⁶⁵Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 103 , rowspan=2, 164.95329(43)# , rowspan=2, , β⁻ (98.64%) , ¹⁶⁵Eu , rowspan=2, 5/2−# , rowspan=2, , rowspan=2, , - , β⁻, n (1.36%) , ¹⁶⁴Eu , -id=Samarium-166 , rowspan=2, ¹⁶⁶Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 104 , rowspan=2, 165.95658(43)# , rowspan=2, , β⁻ (95.62%) , ¹⁶⁶Eu , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (4.38%) , ¹⁶⁵Eu , -id=Samarium-167 , rowspan=2, ¹⁶⁷Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 105 , rowspan=2, 166.96207(54)# , rowspan=2, , β⁻ , ¹⁶⁷Eu , rowspan=2, 7/2−# , rowspan=2, , rowspan=2, , - , β⁻, n (<16%) , ¹⁶⁶Eu , -id=Samarium-168 , rowspan=2, ¹⁶⁸Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 106 , rowspan=2, 167.96603(32)# , rowspan=2, , β⁻ , ¹⁶⁸Eu , rowspan=2, 0+# , rowspan=2, , rowspan=2, , - , β⁻, n (<21%) , ¹⁶⁷Eu

Samarium-149

Samarium-149 (¹⁴⁹Sm) is an observationally stable isotope of

(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

¹⁴⁹Nd (yield 1.0888%). ¹⁴⁹Sm is a

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

-absorbing

nuclear poison In applications such as nuclear reactors, a neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section. In such applications, absorbing neutrons is normally an undesirable ef ...

with significant effect on

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

operation, second only to ¹³⁵Xe. Its

neutron cross section In nuclear physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. The neutron cross section σ can be defined as the area in cm2 for which the number of ...

is 40140

barn A barn is an agricultural building usually on farms and used for various purposes. In North America, a barn refers to structures that house livestock, including cattle and horses, as well as equipment and fodder, and often grain.Allen G ...

s for

thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium wit ...

s. 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 Xenon-135 (135Xe) is an Isotope#Radioactive, primordial, and stable isotopes, unstable isotope of xenon with a half-life of about 9.2 hours. 135Xe is a fission product of uranium and it is the most powerful known neutron-absorbing nuclear poison ...

, which accumulates from the beta decay of

iodine-135 There are 40 known isotopes of iodine (53I) from 108I to 147I; all undergo radioactive decay except 127I, which is stable. Iodine is thus a monoisotopic element. Its longest-lived radioactive isotope, 129I, has a half-life of 16.14 million yea ...

(a short lived

) 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.

Samarium-151

Samarium-151 (¹⁵¹Sm) has a

of 94.6 years, undergoing low-energy beta decay, and has a

fission product yield Nuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a fission product produced per fission. Yield can be broken down by: # Individual i ...

of 0.4203% for thermal neutrons and ²³⁵U, about 39% of ¹⁴⁹Sm's yield. The yield is somewhat higher for ²³⁹Pu. Its

neutron absorption Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture and engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **A ...

for

s is high at 15200

s, about 38% of ¹⁴⁹Sm's absorption cross section, or about 20 times that of ²³⁵U. Since the ratios between the production and absorption rates of ¹⁵¹Sm and ¹⁴⁹Sm are almost equal, the two isotopes should reach similar equilibrium concentrations. Since ¹⁴⁹Sm reaches equilibrium in about 500 hours (20 days), ¹⁵¹Sm should reach equilibrium in about 50 days. Since nuclear fuel is used for several years (

burnup In nuclear power technology, burnup is a measure of how much energy is extracted from a given amount of nuclear fuel. It may be measured as the fraction of fuel atoms that underwent fission in %FIMA (fissions per initial heavy metal atom) or %FIF ...

) in a

nuclear power plant A nuclear power plant (NPP), also known as a nuclear power station (NPS), nuclear generating station (NGS) or atomic power station (APS) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power st ...

, the final amount of ¹⁵¹Sm in the

spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and ...

at discharge is only a small fraction of the total ¹⁵¹Sm produced during the use of the fuel. According to one study, the mass fraction of ¹⁵¹Sm in spent fuel is about 0.0025 for heavy loading of

MOX fuel Mixed oxide fuel (MOX fuel) is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enr ...

and about half that for uranium fuel, which is roughly two orders of magnitude less than the mass fraction of about 0.15 for the

¹³⁷Cs. Figure 2, page 6 The

decay energy The decay energy is the energy change of a nucleus having undergone a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energ ...

of ¹⁵¹Sm is also about an order of magnitude less than that of ¹³⁷Cs. The low yield, low survival rate, and low

mean that ¹⁵¹Sm has insignificant

nuclear waste Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...

impact compared to the two main

s ¹³⁷Cs and ⁹⁰Sr.
ANL factsheet

Samarium-153

Samarium-153 (¹⁵³Sm) has a half-life of 46.3 hours, undergoing β⁻ decay into ¹⁵³Eu. As a component of samarium lexidronam, it is used in palliation of

bone cancer A bone tumor is an neoplastic, abnormal growth of tissue in bone, traditionally classified as benign, noncancerous (benign) or malignant, cancerous (malignant). Cancerous bone tumors usually originate from a cancer in another part of the body su ...

. It is treated by the body in a similar manner to calcium, and it localizes selectively to

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

References

{{Navbox element isotopes Samarium

Samarium Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of s ...

List of isotopes

Samarium-149

Samarium-151

Samarium-153

See also

References