Isotopes of uranium
Encyclopedia
Uranium
(U) is a naturally occurring radioactive element that has no stable isotope
s but two primordial isotopes (uranium-238
and uranium-235
) that have long half-life
and are found in appreciable quantity in the Earth's crust, along with the decay product
uranium-234. The average atomic mass
of natural uranium
is 238.02891(3) u. Other isotopes such as uranium-232 have been produced in breeder reactor
s.
Naturally occurring uranium is composed of three major isotope
s, uranium-238
(99.28% natural abundance
), uranium-235
(0.71%), and uranium-234 (0.0054%). All three isotopes are radioactive
, creating radioisotope
s, with the most abundant and stable being uranium-238 with a half-life
of 4.4683 years (close to the age of the Earth
), uranium-235 with a half-life of 7.038 years, and uranium-234 with a half-life of 2.48 years.
Uranium-238 is an α
emitter, decaying through the 18-member uranium series into lead-206. The decay series of uranium-235 (historically called actino-uranium) has 15 members that ends in lead-207. The constant rates of decay in these series makes comparison of the ratios of parent to daughter elements useful in radiometric dating
. Uranium-233
is made from thorium-232 by neutron
bombardment.
The isotope uranium-235 is important for both nuclear reactor
s and nuclear weapon
s because it is the only isotope existing in nature to any appreciable extent that is fissile
, that is, can be broken apart by thermal neutrons. The isotope uranium-238 is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope plutonium-239
, which also is fissile.
to neutron
radiation
in a nuclear reactor. 239U has a half-life of about 23.45 minutes and decays into neptunium-239 through beta decay
, with a total decay energy of about 1.29 Mev.. The most common gamma decay at 74.660 kev accounts for the difference in the two major channels of beta emission energy, at 1.28 and 1.21 Mev.
239Np further decays to plutonium-239
, in a second important step which ultimately produces fissile 239Pu (used in weapons and for nuclear power), from 238U in reactors.
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
(U) is a naturally occurring radioactive element that has no stable isotope
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
s but two primordial isotopes (uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
and uranium-235
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...
) that have long 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...
and are found in appreciable quantity in the Earth's crust, along with the decay product
Decay product
In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...
uranium-234. The average atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....
of natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...
is 238.02891(3) u. Other isotopes such as uranium-232 have been produced in breeder reactor
Breeder reactor
A breeder reactor is a nuclear reactor capable of generating more fissile material than it consumes because its neutron economy is high enough to breed fissile from fertile material like uranium-238 or thorium-232. Breeders were at first considered superior because of their superior fuel economy...
s.
Naturally occurring uranium is composed of three major 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, uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
(99.28% 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...
), uranium-235
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...
(0.71%), and uranium-234 (0.0054%). All three isotopes are radioactive
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
, creating radioisotope
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
s, with the most abundant and stable being uranium-238 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...
of 4.4683 years (close to the age of the Earth
Age of the Earth
The age of the Earth is 4.54 billion years This age is based on evidence from radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples...
), uranium-235 with a half-life of 7.038 years, and uranium-234 with a half-life of 2.48 years.
Uranium-238 is an 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...
emitter, decaying through the 18-member uranium series into lead-206. The decay series of uranium-235 (historically called actino-uranium) has 15 members that ends in lead-207. The constant rates of decay in these series makes comparison of the ratios of parent to daughter elements useful in radiometric dating
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
. Uranium-233
Uranium-233
Uranium-233 is a fissile isotope of uranium, bred from Thorium as part of the thorium fuel cycle. It has been used in a few nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of 160,000 years....
is made from thorium-232 by 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...
bombardment.
The isotope uranium-235 is important for both 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...
s and nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s because it is the only isotope existing in nature to any appreciable extent that is fissile
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
, that is, can be broken apart by thermal neutrons. The isotope uranium-238 is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope plutonium-239
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...
, which also is fissile.
Uranium-239
Uranium-239 is an isotope of uranium. It is usually produced by exposing 238UUranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
to 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...
radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
in a nuclear reactor. 239U has a half-life of about 23.45 minutes and decays into neptunium-239 through 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...
, with a total decay energy of about 1.29 Mev.. The most common gamma decay at 74.660 kev accounts for the difference in the two major channels of beta emission energy, at 1.28 and 1.21 Mev.
239Np further decays to plutonium-239
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...
, in a second important step which ultimately produces fissile 239Pu (used in weapons and for nuclear power), from 238U in reactors.
Table
| nuclide symbol |
historic name |
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-life | decay mode(s)Abbreviations: CD: Cluster decay Cluster decay Cluster decay is a type of nuclear decay in which a parent atomic nucleus with A nucleons and Z protons emits a cluster of Ne neutrons and Ze protons heavier than an alpha particle but lighter than a typical binary fission fragment Cluster decay (also named heavy particle radioactivity or heavy... 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.... SF: Spontaneous fission Spontaneous fission Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses... |
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 | ||||||||||
| 217U | 92 | 125 | 217.02437(9) | 26(14) ms [16(+21-6) ms] |
1/2-# | |||||
| 218U | 92 | 126 | 218.02354(3) | 6(5) ms | 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... |
214Th | 0+ | |||
| 219U | 92 | 127 | 219.02492(6) | 55(25) ms [42(+34-13) ms] |
α | 215Th | 9/2+# | |||
| 220U | 92 | 128 | 220.02472(22)# | 60# ns | α | 216Th | 0+ | |||
| β+ (rare) | 220Pa | |||||||||
| 221U | 92 | 129 | 221.02640(11)# | 700# ns | α | 217Th | 9/2+# | |||
| β+ (rare) | 221Pa | |||||||||
| 222U | 92 | 130 | 222.02609(11)# | 1.4(7) ms [1.0(+10-4) ms] |
α | 218Th | 0+ | |||
| β+ (10−6%) | 222Pa | |||||||||
| 223U | 92 | 131 | 223.02774(8) | 21(8) ms [18(+10-5) ms] |
α | 219Th | 7/2+# | |||
| 224U | 92 | 132 | 224.027605(27) | 940(270) ms | α | 220Th | 0+ | |||
| 225U | 92 | 133 | 225.02939# | 61(4) ms | α | 221Th | (5/2+)# | |||
| 226U | 92 | 134 | 226.029339(14) | 269(6) ms | α | 222Th | 0+ | |||
| 227U | 92 | 135 | 227.031156(18) | 1.1(1) min | α | 223Th | (3/2+) | |||
| β+ (.001%) | 227Pa | |||||||||
| 228U | 92 | 136 | 228.031374(16) | 9.1(2) min | α (95%) | 224Th | 0+ | |||
| EC Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... (5%) |
228Pa | |||||||||
| 229U | 92 | 137 | 229.033506(6) | 58(3) min | β+ (80%) | 229Pa | (3/2+) | |||
| α (20%) | 225Th | |||||||||
| 230U | 92 | 138 | 230.033940(5) | 20.8 d | α | 226Th | 0+ | |||
| SF Spontaneous fission Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses... (1.4×10−10%) |
(various) | |||||||||
| β+β+ (rare) | 230Th | |||||||||
| 231U | 92 | 139 | 231.036294(3) | 4.2(1) d | EC | 231Pa | (5/2)(+#) | |||
| α (.004%) | 227Th | |||||||||
| 232U | 92 | 140 | 232.0371562(24) | 68.9(4) y | α | 228Th | 0+ | |||
| CD Cluster decay Cluster decay is a type of nuclear decay in which a parent atomic nucleus with A nucleons and Z protons emits a cluster of Ne neutrons and Ze protons heavier than an alpha particle but lighter than a typical binary fission fragment Cluster decay (also named heavy particle radioactivity or heavy... (8.9×10−10%) |
208Pb 24Ne |
|||||||||
| CD (5×10−12%) | 204Hg 28Mg |
|||||||||
| SF (10−12%) | (various) | |||||||||
| 233U Uranium-233 Uranium-233 is a fissile isotope of uranium, bred from Thorium as part of the thorium fuel cycle. It has been used in a few nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of 160,000 years.... |
92 | 141 | 233.0396352(29) | 1.592(2)×105 y | α | 229Th | 5/2+ | |||
| SF (6×10−9%) | (various) | |||||||||
| CD (7.2×10−11%) | 209Pb 24Ne |
|||||||||
| CD (1.3×10−13%) | 205Hg 28Mg |
|||||||||
| 234UUsed in uranium-thorium dating Uranium-thorium dating Uranium-thorium dating, also called thorium-230 dating, uranium-series disequilibrium dating or uranium-series dating, is a radiometric dating technique commonly used to determine the age of calcium carbonate materials such as speleothem or coral... Used in uranium-uranium dating Uranium-uranium dating Uranium-uranium dating is a radiometric dating technique which compares two isotopes of uranium in a sample: 234U and 238U. 234U/238U dating is one of several radiometric dating techniques exploiting the uranium radioactive decay series, in which 238U undergoes 14 alpha and beta decay events... |
Uranium II | 92 | 142 | 234.0409521(20) | 2.455(6)×105 y | α | 230Th | 0+ | [0.000054(5)]Intermediate decay product Decay product In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps... of 238U Uranium-238 Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239... |
0.000050- 0.000059 |
| SF (1.73×10−9%) | (various) | |||||||||
| CD (1.4×10−11%) | 206Hg 28Mg |
|||||||||
| CD (9×10−12%) | 184Hf 26Ne 24Ne |
|||||||||
| 234mU | 1421.32(10) keV | 33.5(20) ms | 6- | |||||||
| 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... Primordial 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... radionuclide Radionuclide A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma... Used in Uranium-lead dating Uranium-lead dating Uranium-lead is one of the oldest and most refined of the radiometric dating schemes, with a routine age range of about 1 million years to over 4.5 billion years, and with routine precisions in the 0.1-1 percent range... Important in nuclear reactors |
Actin Uranium Actino-Uranium |
92 | 143 | 235.0439299(20) | 7.04(1)×108 y | α | 231Th | 7/2- | [0.007204(6)] | 0.007198- 0.007207 |
| SF (7×10−9%) | (various) | |||||||||
| CD (8×10−10%) | 186Hf 25Ne 24Ne |
|||||||||
| 235mU | 0.0765(4) keV | ~26 min | 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.... |
235U | 1/2+ | |||||
| 236U Uranium-236 - See also :* Depleted uranium* Uranium market* Nuclear reprocessing* United States Enrichment Corporation* Nuclear fuel cycle* Nuclear power-External links:* *... |
92 | 144 | 236.045568(2) | 2.342(3)×107 y | α | 232Th | 0+ | |||
| SF (9.6×10−8%) | (various) | |||||||||
| 236m1U | 1052.89(19) keV | 100(4) ns | (4)- | |||||||
| 236m2U | 2750(10) keV | 120(2) ns | (0+) | |||||||
| 237U | 92 | 145 | 237.0487302(20) | 6.75(1) d | β- | 237Np | 1/2+ | |||
| 238U Uranium-238 Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239... |
Uranium I | 92 | 146 | 238.0507882(20) | 4.468(3)×109 y | α | 234Th | 0+ | [0.992742(10)] | 0.992739- 0.992752 |
| SF (5.45×10−5%) | (various) | |||||||||
| β-β- (2.19×10−10%) | 238Pu | |||||||||
| 238mU | 2557.9(5) keV | 280(6) ns | 0+ | |||||||
| 239U | 92 | 147 | 239.0542933(21) | 23.45(2) min | β- | 239Np | 5/2+ | |||
| 239m1U | 20(20)# keV | >250 ns | (5/2+) | |||||||
| 239m2U | 133.7990(10) keV | 780(40) ns | 1/2+ | |||||||
| 240U | 92 | 148 | 240.056592(6) | 14.1(1) h | β- | 240Np | 0+ | |||
| α (10−10%) | 236Th | |||||||||
| 241U | 92 | 149 | 241.06033(32)# | 5# min | β- | 241Np | 7/2+# | |||
| 242U | 92 | 150 | 242.06293(22)# | 16.8(5) min | β- | 242Np | 0+ | |||