Naturally occurring samarium (₆₂Sm) is composed of five stable

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass number ...

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 nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

s, ¹⁴⁷Sm (half life: 1.06 y) and ¹⁴⁸Sm (7 y), with ¹⁵²Sm being the most abundant (26.75% natural abundance). ¹⁴⁶Sm 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. Other than the naturally occurring isotopes, the longest-lived radioisotopes are ¹⁵¹Sm, which has a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

of 88.8 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 formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

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) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an a ...

to isotopes of neodymium. 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. T ...

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 ...

, while heavier ones decay by

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For e ...

to isotopes of europium. Isotopes of samarium are used in samarium–neodymium dating for determining the age relationships of rocks and meteorites. ¹⁵¹Sm is a medium-lived fission product and acts as a neutron poison in the

nuclear fuel cycle The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the ''front end'', which are the preparation of the fuel, steps in the ''service period'' in w ...

. 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 release ...

¹⁴⁹Sm is also a neutron poison.

List of isotopes

, - , ¹²⁹Sm , style="text-align:right" , 62 , style="text-align:right" , 67 , 128.95464(54)# , 550(100) ms , , , 5/2+# , , , - , ¹³⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 68 , 129.94892(43)# , 1# s , β⁺ , ¹³⁰Pm , 0+ , , , - , rowspan=2, ¹³¹Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 69 , rowspan=2, 130.94611(32)# , rowspan=2, 1.2(2) s , β⁺ , ¹³¹Pm , rowspan=2, 5/2+# , rowspan=2, , rowspan=2, , - , β⁺, p (rare) , ¹³⁰Nd , - , rowspan=2, ¹³²Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 70 , rowspan=2, 131.94069(32)# , rowspan=2, 4.0(3) s , β⁺ , ¹³²Pm , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺, p , ¹³¹Nd , - , rowspan=2, ¹³³Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 71 , rowspan=2, 132.93867(21)# , rowspan=2, 2.90(17) s , β⁺ , ¹³³Pm , rowspan=2, (5/2+) , rowspan=2, , rowspan=2, , - , β⁺, p , ¹³²Nd , - , ¹³⁴Sm , style="text-align:right" , 62 , style="text-align:right" , 72 , 133.93397(21)# , 10(1) s , β⁺ , ¹³⁴Pm , 0+ , , , - , 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 (.02%) , ¹³⁴Nd , - , style="text-indent:1em" , ^135mSm , colspan="3" style="text-indent:2em" , 0(300)# keV , 2.4(9) s , β⁺ , ¹³⁵Pm , (3/2+, 5/2+) , , , - , ¹³⁶Sm , style="text-align:right" , 62 , style="text-align:right" , 74 , 135.928276(13) , 47(2) s , β⁺ , ¹³⁶Pm , 0+ , , , - , style="text-indent:1em" , ^136mSm , colspan="3" style="text-indent:2em" , 2264.7(11) keV , 15(1) μs , , , (8−) , , , - , ¹³⁷Sm , style="text-align:right" , 62 , style="text-align:right" , 75 , 136.92697(5) , 45(1) s , β⁺ , ¹³⁷Pm , (9/2−) , , , - , style="text-indent:1em" , ^137mSm , colspan="3" style="text-indent:2em" , 180(50)# keV , 20# s , β⁺ , ¹³⁷Pm , 1/2+# , , , - , ¹³⁸Sm , style="text-align:right" , 62 , style="text-align:right" , 76 , 137.923244(13) , 3.1(2) min , β⁺ , ¹³⁸Pm , 0+ , , , - , ¹³⁹Sm , style="text-align:right" , 62 , style="text-align:right" , 77 , 138.922297(12) , 2.57(10) min , β⁺ , ¹³⁹Pm , 1/2+ , , , - , rowspan=2 style="text-indent:1em" , ^139mSm , rowspan=2 colspan="3" style="text-indent:2em" , 457.40(22) keV , rowspan=2, 10.7(6) s , IT (93.7%) , ¹³⁹Sm , rowspan=2, 11/2− , rowspan=2, , rowspan=2, , - , β⁺ (6.3%) , ¹³⁹Pm , - , ¹⁴⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 78 , 139.918995(13) , 14.82(12) min , β⁺ , ¹⁴⁰Pm , 0+ , , , - , ¹⁴¹Sm , style="text-align:right" , 62 , style="text-align:right" , 79 , 140.918476(9) , 10.2(2) min , β⁺ , ¹⁴¹Pm , 1/2+ , , , - , rowspan=2 style="text-indent:1em" , ^141mSm , rowspan=2 colspan="3" style="text-indent:2em" , 176.0(3) keV , rowspan=2, 22.6(2) min , β⁺ (99.69%) , ¹⁴¹Pm , rowspan=2, 11/2− , rowspan=2, , rowspan=2, , - , IT (.31%) , ¹⁴¹Sm , - , ¹⁴²Sm , style="text-align:right" , 62 , style="text-align:right" , 80 , 141.915198(6) , 72.49(5) min , β⁺ , ¹⁴²Pm , 0+ , , , - , ¹⁴³Sm , style="text-align:right" , 62 , style="text-align:right" , 81 , 142.914628(4) , 8.75(8) min , β⁺ , ¹⁴³Pm , 3/2+ , , , - , 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⁺ (.24%) , ¹⁴³Pm , - , style="text-indent:1em" , ^143m2Sm , colspan="3" style="text-indent:2em" , 2793.8(13) keV , 30(3) ms , , , 23/2(−) , , , - , ¹⁴⁴Sm , style="text-align:right" , 62 , style="text-align:right" , 82 , 143.911999(3) , colspan=3 align=center,

Observationally Stable Stable nuclides are nuclides that are not radioactive and so (unlike radionuclides) do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes. T ...

, 0+ , 0.0307(7) , , - , style="text-indent:1em" , ^144mSm , colspan="3" style="text-indent:2em" , 2323.60(8) keV , 880(25) ns , , , 6+ , , , - , ¹⁴⁵Sm , style="text-align:right" , 62 , style="text-align:right" , 83 , 144.913410(3) , 340(3) d , EC , ¹⁴⁵Pm , 7/2− , , , - , style="text-indent:1em" , ^145mSm , colspan="3" style="text-indent:2em" , 8786.2(7) keV , 990(170) ns
.96(+19−15) μs, , , (49/2+) , , , - , ¹⁴⁶Sm , style="text-align:right" , 62 , style="text-align:right" , 84 , 145.913041(4) , 6.8(7)×10⁷ y , α , ¹⁴²Nd , 0+ , Trace , , - , ¹⁴⁷Sm

Primordial Primordial may refer to: * Primordial era, an era after the Big Bang. See Chronology of the universe * Primordial sea (a.k.a. primordial ocean, ooze or soup). See Abiogenesis * Primordial nuclide, nuclides, a few radioactive, that formed before ...

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 release ...

Used in Samarium–neodymium dating , style="text-align:right" , 62 , style="text-align:right" , 85 , 146.9148979(26) , 1.06(2)×10¹¹ y , α , ¹⁴³Nd , 7/2− , 0.1499(18) , , - , ¹⁴⁸Sm , style="text-align:right" , 62 , style="text-align:right" , 86 , 147.9148227(26) , 7(3)×10¹⁵ y , α , ''¹⁴⁴Nd'' , 0+ , 0.1124(10) , , - , ¹⁴⁹Sm Neutron poison in reactors , style="text-align:right" , 62 , style="text-align:right" , 87 , 148.9171847(26) , colspan=3 align=center, Observationally Stable , 7/2− , 0.1382(7) , , - , ¹⁵⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 88 , 149.9172755(26) , colspan=3 align=center, Observationally Stable , 0+ , 0.0738(1) , , - , ¹⁵¹Sm , style="text-align:right" , 62 , style="text-align:right" , 89 , 150.9199324(26) , 88.8(24) y , β⁻ , ''¹⁵¹Eu'' , 5/2− , , , - , style="text-indent:1em" , ^151mSm , colspan="3" style="text-indent:2em" , 261.13(4) keV , 1.4(1) μs , , , (11/2)− , , , - , ¹⁵²Sm , style="text-align:right" , 62 , style="text-align:right" , 90 , 151.9197324(27) , colspan=3 align=center, Observationally Stable , 0+ , 0.2675(16) , , - , ¹⁵³Sm , style="text-align:right" , 62 , style="text-align:right" , 91 , 152.9220974(27) , 46.284(4) h , β⁻ , ¹⁵³Eu , 3/2+ , , , - , style="text-indent:1em" , ^153mSm , colspan="3" style="text-indent:2em" , 98.37(10) keV , 10.6(3) ms , IT , ¹⁵³Sm , 11/2− , , , - , ¹⁵⁴Sm , style="text-align:right" , 62 , style="text-align:right" , 92 , 153.9222093(27) , colspan=3 align=center, Observationally Stable , 0+ , 0.2275(29) , , - , ¹⁵⁵Sm , style="text-align:right" , 62 , style="text-align:right" , 93 , 154.9246402(28) , 22.3(2) min , β⁻ , ¹⁵⁵Eu , 3/2− , , , - , ¹⁵⁶Sm , style="text-align:right" , 62 , style="text-align:right" , 94 , 155.925528(10) , 9.4(2) h , β⁻ , ¹⁵⁶Eu , 0+ , , , - , style="text-indent:1em" , ^156mSm , colspan="3" style="text-indent:2em" , 1397.55(9) keV , 185(7) ns , , , 5− , , , - , ¹⁵⁷Sm , style="text-align:right" , 62 , style="text-align:right" , 95 , 156.92836(5) , 8.03(7) min , β⁻ , ¹⁵⁷Eu , (3/2−) , , , - , ¹⁵⁸Sm , style="text-align:right" , 62 , style="text-align:right" , 96 , 157.92999(8) , 5.30(3) min , β⁻ , ¹⁵⁸Eu , 0+ , , , - , ¹⁵⁹Sm , style="text-align:right" , 62 , style="text-align:right" , 97 , 158.93321(11) , 11.37(15) s , β⁻ , ¹⁵⁹Eu , 5/2− , , , - , ¹⁶⁰Sm , style="text-align:right" , 62 , style="text-align:right" , 98 , 159.93514(21)# , 9.6(3) s , β⁻ , ¹⁶⁰Eu , 0+ , , , - , ¹⁶¹Sm , style="text-align:right" , 62 , style="text-align:right" , 99 , 160.93883(32)# , , β⁻ , ¹⁶¹Eu , 7/2+# , , , - , ¹⁶²Sm , style="text-align:right" , 62 , style="text-align:right" , 100 , 161.94122(54)# , , β⁻ , ¹⁶²Eu , 0+ , , , - , ¹⁶³Sm , style="text-align:right" , 62 , style="text-align:right" , 101 , 162.94536(75)# , , β⁻ , ¹⁶³Eu , 1/2−# , , , - , ¹⁶⁴Sm , style="text-align:right" , 62 , style="text-align:right" , 102 , 163.94828(86)# , , β⁻ , ¹⁶⁴Eu , 0+ , , , - , rowspan=2, ¹⁶⁵Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 103 , rowspan=2, 164.95298(97)# , rowspan=2, , β⁻ (98.64%) , ¹⁶⁵Eu , rowspan=2, 5/2−# , rowspan=2, , rowspan=2, , - , β⁻, n (1.36%) , ¹⁶⁴Eu , - , rowspan=2, ¹⁶⁶Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 104 , rowspan=2, , rowspan=2, , β⁻ (95.62%) , ¹⁶⁶Eu , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n (4.38%) , ¹⁶⁵Eu , - , rowspan=2, ¹⁶⁷Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 105 , rowspan=2, , rowspan=2, , β⁻ , ¹⁶⁷Eu , rowspan=2, , rowspan=2, , rowspan=2, , - , β⁻, n , ¹⁶⁶Eu , - , rowspan=2, ¹⁶⁸Sm , rowspan=2 style="text-align:right" , 62 , rowspan=2 style="text-align:right" , 106 , rowspan=2, , rowspan=2, , β⁻ , ¹⁶⁸Eu , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁻, n , ¹⁶⁷Eu

Samarium-149

Samarium-149 (¹⁴⁹Sm) 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

¹⁴⁹Nd (yield 1.0888%). ¹⁴⁹Sm is a

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

-absorbing nuclear poison with significant effect on

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...

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 ...

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 with ...

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, which accumulates from the beta decay of iodine-135 (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 88.8 years, undergoing low-energy beta decay, and has a fission product yield 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 ...

cross section 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 (also known as fuel utilization) is a measure of how much energy is extracted from a primary nuclear fuel source. It is measured as the fraction of fuel atoms that underwent fission in %FIMA (fissions per init ...

) in a nuclear power plant, 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 an ...

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, commonly referred to as 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 ...

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 medium-lived fission product ¹³⁷Cs. Figure 2, page 6 The decay energy of ¹⁵¹Sm is also about an order of magnitude less than that of ¹³⁷Cs. The low yield, low survival rate, and low decay energy mean that ¹⁵¹Sm has insignificant

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

impact compared to the two main medium-lived fission products 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 abnormal growth of tissue in bone, traditionally classified as noncancerous (benign) or cancerous (malignant). Cancerous bone tumors usually originate from a cancer in another part of the body such as from lung, breast, th ...

. 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, an ...

References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Navbox element isotopes Samarium Samarium