Isotopes of samarium
Encyclopedia
Naturally occurring samarium
(Sm) is composed of five stable isotope
s, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (1.06y) and 148Sm (7y), with 152Sm being the most abundant (26.75% natural abundance
). 146Sm is also fairly long-lived (1.03×108y), but occurs naturally as only the tiniest trace remains from its original supernova nucleosynthesis
.
Other than the naturally occurring isotopes, the longest-lived radioisotopes are 151Sm, which has a half-life
of 90 years, and 145Sm, which has a half-life of 340 days. All of the remaining radioisotopes 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
with the most stable being 141mSm (t½ 22.6 minutes), 143m1Sm (t½ 66 seconds) and 139mSm (t½ 10.7 seconds).
The long lived isotopes,146Sm, 147Sm, and 148Sm primarily decay by alpha decay
to isotopes of neodymium
. Lighter unstable isotopes of samarium primarily decay by electron capture
to isotopes of promethium
, while heavier ones decay by beta minus decay 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 stable fission product
149Sm is also a neutron poison.
Standard atomic mass: 150.36(2) u
, and a fission product
(yield 1.0888%) which is also a neutron
-absorbing nuclear poison
with significant effect on nuclear reactor
operation, second only to 135Xe
. Its neutron cross section is 40140 barn
s for thermal neutrons.
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.
of 90 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 cross section
for thermal neutrons is high at 15200 barn
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 of151Sm 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 a nuclear power plant
, the final amount of 151Sm in the spent nuclear fuel
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 Sm-151 in spent fuel is about 0.0025 for heavy loading of MOX fuel
and about half that for uranium fuel, which is roughly two orders of magnitude less than the mass fraction of about .15 for the medium-lived fission product Cs-137.
The decay energy
of151Sm 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 impact compared to the two main medium-lived fission products 137Cs
and 90Sr
.
Samarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...
(Sm) is composed of five stable isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (1.06y) and 148Sm (7y), with 152Sm being the most abundant (26.75% natural abundance
Natural abundance
In chemistry, natural abundance refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass of these isotopes is the atomic weight listed for the element in the periodic table...
). 146Sm is also fairly long-lived (1.03×108y), but occurs naturally as only the tiniest trace remains from its original supernova nucleosynthesis
Supernova nucleosynthesis
Supernova nucleosynthesis is the production of new chemical elements inside supernovae. It occurs primarily due to explosive nucleosynthesis during explosive oxygen burning and silicon burning...
.
Other than the naturally occurring isotopes, the longest-lived radioisotopes are 151Sm, which has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 90 years, and 145Sm, which has a half-life of 340 days. All of the remaining radioisotopes 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
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
with the most stable being 141mSm (t½ 22.6 minutes), 143m1Sm (t½ 66 seconds) and 139mSm (t½ 10.7 seconds).
The long lived isotopes,146Sm, 147Sm, and 148Sm primarily decay by alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
to isotopes of neodymium
Isotopes of neodymium
Naturally occurring neodymium is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant , and 2 radioisotopes, 144Nd and 150Nd...
. Lighter unstable isotopes of samarium primarily decay by electron capture
Electron capture
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...
to isotopes of promethium
Isotopes of promethium
Promethium has no stable isotopes, and does not exist in nature, except in trace quantities as a product of spontaneous fission. It is a synthetic element, first produced in 1945. Thirty-eight radioisotopes have been characterized, with the most stable being 145Pm with a half-life of 17.7 years,...
, while heavier ones decay by beta minus decay to isotopes of europium
Isotopes of europium
Naturally occurring europium is composed of 2 isotopes, 151Eu and 153Eu, with 153Eu being the most abundant . While 153Eu is stable, 151Eu was recently found to be unstable and to undergo alpha decay with half-life of...
Isotopes of samarium are used in samarium-neodymium dating
Samarium-neodymium dating
Samarium-neodymium dating is useful for determining the age relationships of rocks and meteorites, based on decay of a long-lived samarium isotope to a radiogenic neodymium isotope. Nd isotope ratios are used to provide information on the source of igneous melts as well as to provide age data...
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
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 which the fuel is used during reactor operation, and steps in...
. The stable fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
149Sm is also a neutron poison.
Standard atomic mass: 150.36(2) u
Samarium-149
149Sm is a stable isotope of samariumSamarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...
, and a fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
(yield 1.0888%) which is also a neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
-absorbing nuclear poison
Nuclear poison
A neutron poison is a substance with a large neutron absorption cross-section in applications, such as nuclear reactors. In such applications, absorbing neutrons is normally an undesirable effect...
with significant effect on nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
operation, second only to 135Xe
Xenon-135
Xenon-135 is an unstable isotope of xenon with a half-life of about 9.2 hours. 135Xe is a fission product of uranium and Xe-135 is the most powerful known neutron-absorbing nuclear poison , with a significant effect on nuclear reactor operation...
. Its neutron cross section is 40140 barn
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
s for thermal neutrons.
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.
Samarium-151
has a half-lifeHalf-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 90 years, undergoing low-energy beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
, and has a fission product yield
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 isotope...
of 0.4203% for thermal neutrons and 235U
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
, about 39% of 149Sm's yield. The yield is somewhat higher for 239Pu
Plutonium-239
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
.
Its neutron absorption cross section
Neutron cross-section
In nuclear and particle physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. In conjunction with the neutron flux, it enables the calculation of the reaction rate, for example to derive the thermal power...
for thermal neutrons is high at 15200 barn
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
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 of151Sm 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
Burnup
In nuclear power technology, burnup is a measure of how much energy is extracted from a primary nuclear fuel source...
) in a nuclear power plant
Nuclear power plant
A nuclear power plant is a thermal power station in which the heat source is one or more nuclear reactors. As in a conventional thermal power station the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity.Nuclear power plants are usually...
, the final amount of 151Sm in the spent nuclear fuel
Spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor...
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 Sm-151 in spent fuel is about 0.0025 for heavy loading of MOX fuel
MOX fuel
Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material. MOX fuel contains plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium fuel used in the...
and about half that for uranium fuel, which is roughly two orders of magnitude less than the mass fraction of about .15 for the medium-lived fission product Cs-137.
The decay energy
Decay energy
The decay energy is the energy released by a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation...
of151Sm is also about an order of magnitude less than that of 137Cs. The low yield, low survival rate, and low decay energy
Decay energy
The decay energy is the energy released by a radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation...
mean that 151Sm has insignificant nuclear waste impact compared to the two main medium-lived fission products 137Cs
Caesium-137
Caesium-137 is a radioactive isotope of caesium which is formed as a fission product by nuclear fission.It has a half-life of about 30.17 years, and decays by beta emission to a metastable nuclear isomer of barium-137: barium-137m . Caesium-137 is a radioactive isotope of caesium which is formed...
and 90Sr
Strontium-90
Strontium-90 is a radioactive isotope of strontium, with a half-life of 28.8 years.-Radioactivity:Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...
.
Table
| nuclide symbol |
Z(p Proton The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number.... ) |
N(n Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... ) |
isotopic mass (u) |
half-lifeBold for isotopes with half-lives longer than the age of the universe (nearly stable) | decay mode(s)Abbreviations: EC: Electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... IT: Isomeric transition Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer.... |
daughter isotope(s)Bold for stable isotopes, bold italics for nearly stable isotopes (half-life longer than the age of the universe Age of the universe The age of the universe is the time elapsed since the Big Bang posited by the most widely accepted scientific model of cosmology. The best current estimate of the age of the universe is 13.75 ± 0.13 billion years within the Lambda-CDM concordance model... ) |
nuclear spin |
representative isotopic composition (mole fraction) |
range of natural variation (mole fraction) |
|---|---|---|---|---|---|---|---|---|---|
| excitation energy | |||||||||
| 128Sm | 62 | 66 | 127.95808(54)# | 0.5# s | 0+ | ||||
| 129Sm | 62 | 67 | 128.95464(54)# | 550(100) ms | 5/2+# | ||||
| 130Sm | 62 | 68 | 129.94892(43)# | 1# s | β+ Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
130Pm | 0+ | ||
| 131Sm | 62 | 69 | 130.94611(32)# | 1.2(2) s | β+ | 131Pm | 5/2+# | ||
| β+, p Proton emission Proton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very... (rare) |
130Nd | ||||||||
| 132Sm | 62 | 70 | 131.94069(32)# | 4.0(3) s | β+ | 132Pm | 0+ | ||
| β+, p | 131Nd | ||||||||
| 133Sm | 62 | 71 | 132.93867(21)# | 2.90(17) s | β+ | 133Pm | (5/2+) | ||
| β+, p | 132Nd | ||||||||
| 134Sm | 62 | 72 | 133.93397(21)# | 10(1) s | β+ | 134Pm | 0+ | ||
| 135Sm | 62 | 73 | 134.93252(17) | 10.3(5) s | β+ (99.98%) | 135Pm | (7/2+) | ||
| β+, p (.02%) | 134Nd | ||||||||
| 135mSm | 0(300)# keV | 2.4(9) s | β+ | 135Pm | (3/2+,5/2+) | ||||
| 136Sm | 62 | 74 | 135.928276(13) | 47(2) s | β+ | 136Pm | 0+ | ||
| 136mSm | 2264.7(11) keV | 15(1) µs | (8-) | ||||||
| 137Sm | 62 | 75 | 136.92697(5) | 45(1) s | β+ | 137Pm | (9/2-) | ||
| 137mSm | 180(50)# keV | 20# s | β+ | 137Pm | 1/2+# | ||||
| 138Sm | 62 | 76 | 137.923244(13) | 3.1(2) min | β+ | 138Pm | 0+ | ||
| 139Sm | 62 | 77 | 138.922297(12) | 2.57(10) min | β+ | 139Pm | 1/2+ | ||
| 139mSm | 457.40(22) keV | 10.7(6) s | IT Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer.... (93.7%) |
139Sm | 11/2- | ||||
| β+ (6.3%) | 139Pm | ||||||||
| 140Sm | 62 | 78 | 139.918995(13) | 14.82(12) min | β+ | 140Pm | 0+ | ||
| 141Sm | 62 | 79 | 140.918476(9) | 10.2(2) min | β+ | 141Pm | 1/2+ | ||
| 141mSm | 176.0(3) keV | 22.6(2) min | β+ (99.69%) | 141Pm | 11/2- | ||||
| IT (.31%) | 141Sm | ||||||||
| 142Sm | 62 | 80 | 141.915198(6) | 72.49(5) min | β+ | 142Pm | 0+ | ||
| 143Sm | 62 | 81 | 142.914628(4) | 8.75(8) min | β+ | 143Pm | 3/2+ | ||
| 143m1Sm | 753.99(16) keV | 66(2) s | IT (99.76%) | 143Sm | 11/2- | ||||
| β+ (.24%) | 143Pm | ||||||||
| 143m2Sm | 2793.8(13) keV | 30(3) ms | 23/2(-) | ||||||
| 144Sm | 62 | 82 | 143.911999(3) | Observationally StableBelieved to undergo α decay to 140Nd or β+β+ decay to 144Nd | 0+ | 0.0307(7) | |||
| 144mSm | 2323.60(8) keV | 880(25) ns | 6+ | ||||||
| 145Sm | 62 | 83 | 144.913410(3) | 340(3) d | EC | 145Pm | 7/2- | ||
| 145mSm | 8786.2(7) keV | 990(170) ns [0.96(+19-15) µs] |
(49/2+) | ||||||
| 146SmPrimordial Primordial nuclide In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known... radioisotope |
62 | 84 | 145.913041(4) | 1.03(5)×108 a | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
142Nd | 0+ | Trace | |
| 147SmFission product Fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The... Used in Samarium-neodymium dating Samarium-neodymium dating Samarium-neodymium dating is useful for determining the age relationships of rocks and meteorites, based on decay of a long-lived samarium isotope to a radiogenic neodymium isotope. Nd isotope ratios are used to provide information on the source of igneous melts as well as to provide age data... |
62 | 85 | 146.9148979(26) | 1.06(2)×1011 a | α | 143Nd | 7/2- | 0.1499(18) | |
| 148Sm | 62 | 86 | 147.9148227(26) | 7(3)×1015 a | α | 144Nd | 0+ | 0.1124(10) | |
| 149SmNeutron poison in reactors | 62 | 87 | 148.9171847(26) | Observationally StableBelieved to undergo α decay to 145Nd with a half-life over 2×1015 years | 7/2- | 0.1382(7) | |||
| 150Sm | 62 | 88 | 149.9172755(26) | Observationally StableBelieved to undergo α decay to 146Nd | 0+ | 0.0738(1) | |||
| 151Sm | 62 | 89 | 150.9199324(26) | 90(8) a | β- | 151Eu | 5/2- | ||
| 151mSm | 261.13(4) keV | 1.4(1) µs | (11/2)- | ||||||
| 152Sm | 62 | 90 | 151.9197324(27) | Observationally StableBelieved to undergo α decay to 148Nd | 0+ | 0.2675(16) | |||
| 153Sm | 62 | 91 | 152.9220974(27) | 46.284(4) h | β- | 153Eu | 3/2+ | ||
| 153mSm | 98.37(10) keV | 10.6(3) ms | IT | 153Sm | 11/2- | ||||
| 154Sm | 62 | 92 | 153.9222093(27) | Observationally StableBelieved to undergo β-β- decay to 154Gd with a half-life Half-life Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to... over 2.3×1018 years |
0+ | 0.2275(29) | |||
| 155Sm | 62 | 93 | 154.9246402(28) | 22.3(2) min | β- | 155Eu | 3/2- | ||
| 156Sm | 62 | 94 | 155.925528(10) | 9.4(2) h | β- | 156Eu | 0+ | ||
| 156mSm | 1397.55(9) keV | 185(7) ns | 5- | ||||||
| 157Sm | 62 | 95 | 156.92836(5) | 8.03(7) min | β- | 157Eu | (3/2-) | ||
| 158Sm | 62 | 96 | 157.92999(8) | 5.30(3) min | β- | 158Eu | 0+ | ||
| 159Sm | 62 | 97 | 158.93321(11) | 11.37(15) s | β- | 159Eu | 5/2- | ||
| 160Sm | 62 | 98 | 159.93514(21)# | 9.6(3) s | β- | 160Eu | 0+ | ||
| 161Sm | 62 | 99 | 160.93883(32)# | 4.8(8) s | β- | 161Eu | 7/2+# | ||
| 162Sm | 62 | 100 | 161.94122(54)# | 2.4(5) s | β- | 162Eu | 0+ | ||
| 163Sm | 62 | 101 | 162.94536(75)# | 1# s | β- | 163Eu | 1/2-# | ||
| 164Sm | 62 | 102 | 163.94828(86)# | 500# ms | β- | 164Eu | 0+ | ||
| 165Sm | 62 | 103 | 164.95298(97)# | 200# ms | β- | 165Eu | 5/2-# | ||