Uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

(U) is a naturally occurring radioactive element (radioelement) with no

stable isotope Stable nuclides are Isotope, isotopes of a chemical element whose Nucleon, nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The Atomic nucleus, nuclei of such isotopes are no ...

s. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in

Earth's crust Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper ...

. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors. In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from U to U (except for U). The standard atomic weight of natural uranium is . Natural uranium consists of three main

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, U (99.2739–99.2752% natural abundance), U (0.7198–0.7202%), and U (0.0050–0.0059%). All three isotopes are radioactive (i.e., they are radioisotopes), and the most abundant and stable is uranium-238, with a half-life of (about the

age of the Earth The age of Earth is estimated to be 4.54 ± 0.05 billion years. This age may represent the age of Earth's accretion (astrophysics), accretion, or Internal structure of Earth, core formation, or of the material from which Earth formed. This dating ...

). Uranium-238 is an alpha emitter, decaying through the 18-member uranium series into lead-206. The decay series of uranium-235 (historically called actino-uranium) has 15 members and 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, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...

. Uranium-233 is made from thorium-232 by

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 ...

bombardment. Uranium-235 is important for both

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 ...

s (energy production) and

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

s because it is the only isotope existing in nature to any appreciable extent that is fissile in response to thermal neutrons, i.e., thermal

neutron capture 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 ...

has a high probability of inducing fission. A chain reaction can be sustained with a large enough ( critical) mass of uranium-235. Uranium-238 is also important because it is fertile: it absorbs neutrons to produce a radioactive isotope that decays into plutonium-239, which also is fissile.

List of isotopes

, - , U , , style="text-align:right" , 92 , style="text-align:right" , 122 , , , α , Th , 0+ , , , -id=Uranium-215 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 123 , rowspan=2, 215.026720(11) , rowspan=2, 1.4(9) ms , α , Th , rowspan=2, 5/2−# , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-216 , U , , style="text-align:right" , 92 , style="text-align:right" , 124 , 216.024760(30) , , α , Th , 0+ , , , -id=Uranium-216m , style="text-indent:1em" , U , , colspan="3" style="text-indent:2em" , 2206 keV , , α , Th , 8+ , , , -id=Uranium-217 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 125 , rowspan=2, 217.024660(86)# , rowspan=2, , α , Th , rowspan=2, (1/2−) , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-218 , U , , style="text-align:right" , 92 , style="text-align:right" , 126 , 218.023505(15) , , α , Th , 0+ , , , -id=Uranium-218m , rowspan=2 style="text-indent:1em" , U , rowspan=2, , rowspan=2 colspan="3" style="text-indent:2em" , 2117 keV , rowspan=2, , α , Th , rowspan=2, 8+ , rowspan=2, , rowspan=2, , - , IT? , U , -id=Uranium-219 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 127 , rowspan=2, 219.025009(14) , rowspan=2, 60(7) μs , α , Th , rowspan=2, (9/2+) , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-221 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 129 , rowspan=2, 221.026323(77) , rowspan=2, 0.66(14) μs , α , Th , rowspan=2, (9/2+) , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-222 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 130 , rowspan=2, 222.026058(56) , rowspan=2, 4.7(7) μs , α , Th , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-223 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 131 , rowspan=2, 223.027961(63) , rowspan=2, 65(12) μs , α , Th , rowspan=2, 7/2+# , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-224 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 132 , rowspan=2, 224.027636(16) , rowspan=2, 396(17) μs , α , Th , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-225 , U , , style="text-align:right" , 92 , style="text-align:right" , 133 , 225.029385(11) , 62(4) ms , α , Th , 5/2+# , , , -id=Uranium-226 , U , , style="text-align:right" , 92 , style="text-align:right" , 134 , 226.029339(12) , 269(6) ms , α , Th , 0+ , , , -id=Uranium-227 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 135 , rowspan=2, 227.0311811(91) , rowspan=2, 1.1(1) min , α , Th , rowspan=2, (3/2+) , rowspan=2, , rowspan=2, , - , β? , Pa , -id=Uranium-228 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 136 , rowspan=2, 228.031369(14) , rowspan=2, 9.1(2) min , α (97.5%) , Th , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , EC (2.5%) , Pa , -id=Uranium-229 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 137 , rowspan=2, 229.0335060(64) , rowspan=2, 57.8(5) min , β (80%) , Pa , rowspan=2, (3/2+) , rowspan=2, , rowspan=2, , - , α (20%) , Th , -id=Uranium-230 , rowspan=3, U , rowspan=3, , rowspan=3 style="text-align:right" , 92 , rowspan=3 style="text-align:right" , 138 , rowspan=3, 230.0339401(48) , rowspan=3, 20.23(2) d , α , Th , rowspan=3, 0+ , rowspan=3, , rowspan=3, , - , SF ? , (various) , - , CD (4.8×10%) , Pb
Ne , -id=Uranium-231 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 139 , rowspan=2, 231.0362922(29) , rowspan=2, 4.2(1) d , EC , Pa , rowspan=2, 5/2+# , rowspan=2, , rowspan=2, , - , α (.004%) , Th , - , rowspan=4, U , rowspan=4, , rowspan=4 style="text-align:right" , 92 , rowspan=4 style="text-align:right" , 140 , rowspan=4, 232.0371548(19) , rowspan=4, 68.9(4) y , α , Th , rowspan=4, 0+ , rowspan=4, , rowspan=4, , - , CD (8.9×10%) , Pb
Ne , - , SF (10%) , (various) , - , CD? , Hg
Mg , - , rowspan=4, U , rowspan=4, , rowspan=4 style="text-align:right" , 92 , rowspan=4 style="text-align:right" , 141 , rowspan=4, 233.0396343(24) , rowspan=4, 1.592(2)×10 y , α , Th , rowspan=4, 5/2+ , rowspan=4, TraceIntermediate decay product of Np , rowspan=4, , - , CD (≤7.2×10%) , Pb
Ne , - , SF ? , (various) , - , CD ? , Hg
Mg , - , rowspan=5, UUsed in uranium–thorium datingUsed in uranium–uranium dating , rowspan=5, Uranium II , rowspan=5 style="text-align:right" , 92 , rowspan=5 style="text-align:right" , 142 , rowspan=5, 234.0409503(12) , rowspan=5, 2.455(6)×10 y , α , Th , rowspan=5, 0+ , rowspan=5, .000054(5)ref group="n">Intermediate decay product of U , rowspan=5, 0.000050–
0.000059 , - , SF (1.64×10%) , (various) , - , CD (1.4×10%) , Hg
Mg , - , CD (≤9×10%) , Pb
Ne , - , CD (≤9×10%) , Pb
Ne , -id=Uranium-234m , style="text-indent:1em" , U , , colspan="3" style="text-indent:2em" , 1421.257(17) keV , 33.5(20) ms , IT , U , 6− , , , - , rowspan=5, UPrimordial radionuclideUsed in Uranium–lead datingImportant in nuclear reactors , rowspan=5, Actin Uranium
Actino-Uranium , rowspan=5 style="text-align:right" , 92 , rowspan=5 style="text-align:right" , 143 , rowspan=5, 235.0439281(12) , rowspan=5, 7.038(1)×10 y , α , Th , rowspan=5, 7/2− , rowspan=5, .007204(6), rowspan=5, 0.007198–
0.007207 , - , SF (7×10%) , (various) , - , CD (8×10%) , Pb
Ne , - , CD (8×10%) , Pb
Ne , - , CD (8×10%) , Hg
Mg , -id=Uranium-235m1 , style="text-indent:1em" , U , , colspan="3" style="text-indent:2em" , 0.076737(18) keV , 25.7(1) min , IT , ''U'' , 1/2+ , , , -id=Uranium-235m2 , style="text-indent:1em" , U , , colspan="3" style="text-indent:2em" , 2500(300) keV , 3.6(18) ms , SF , (various) , , , , - , rowspan=4, U , rowspan=4, Thoruranium , rowspan=4 style="text-align:right" , 92 , rowspan=4 style="text-align:right" , 144 , rowspan=4, 236.0455661(12) , rowspan=4, 2.342(3)×10 y , α , ''Th'' , rowspan=4, 0+ , rowspan=4, TraceIntermediate decay product of Pu, also produced by

of U , rowspan=4, , - , SF (9.6×10%) , (various) , - , CD (≤2.0×10%) , Hg
Mg , - , CD (≤2.0×10%) , Hg
Mg , -id=Uranium-236m1 , style="text-indent:1em" , U , , colspan="3" style="text-indent:2em" , 1052.5(6) keV , 100(4) ns , IT , U , 4− , , , -id=Uranium-236m2 , rowspan=2 style="text-indent:1em" , U , rowspan=2, , rowspan=2 colspan="3" style="text-indent:2em" , 2750(3) keV , rowspan=2, 120(2) ns , IT (87%) , U , rowspan=2, (0+) , rowspan=2, , rowspan=2, , - , SF (13%) , (various) , - , U , , style="text-align:right" , 92 , style="text-align:right" , 145 , 237.0487283(13) , 6.752(2) d , β , Np , 1/2+ , TraceNeutron capture product, parent of trace quantities of Np , , -id=Uranium-237m , style="text-indent:1em" , U , , colspan="3" style="text-indent:2em" , 274.0(10) keV , 155(6) ns , IT , U , 7/2− , , , - , rowspan=3, U , rowspan=3, Uranium I , rowspan=3 style="text-align:right" , 92 , rowspan=3 style="text-align:right" , 146 , rowspan=3, 238.050787618(15) , rowspan=3, 4.468(3)×10 y , α , Th , rowspan=3, 0+ , rowspan=3, .992742(10), rowspan=3, 0.992739–
0.992752 , - , SF (5.44×10%) , (various) , - , ββ (2.2×10%) , Pu , -id=Uranium-238m , rowspan=2 style="text-indent:1em" , U , rowspan=2, , rowspan=2 colspan="3" style="text-indent:2em" , 2557.9(5) keV , rowspan=2, 280(6) ns , IT (97.4%) , ''U'' , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , SF (2.6%) , (various) , - , U , , style="text-align:right" , 92 , style="text-align:right" , 147 , 239.0542920(16) , 23.45(2) min , β , Np , 5/2+ , TraceNeutron capture product; parent of trace quantities of Pu , , -id=Uranium-239m1 , style="text-indent:1em" , U , , colspan="3" style="text-indent:2em" , 133.7991(10) keV , 780(40) ns , IT , U , 1/2+ , , , -id=Uranium-239m2 , rowspan=2 style="text-indent:1em" , U , rowspan=2, , rowspan=2 colspan="3" style="text-indent:2em" , 2500(900)# keV , rowspan=2, >250 ns , SF? , (various) , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , IT? , U , -id=Uranium-240 , rowspan=2, U , rowspan=2, , rowspan=2 style="text-align:right" , 92 , rowspan=2 style="text-align:right" , 148 , rowspan=2, 240.0565924(27) , rowspan=2, 14.1(1) h , β , Np , rowspan=2, 0+ , rowspan=2, TraceIntermediate decay product of Pu , rowspan=2, , - , α? , Th , - , U , , style="text-align:right" , 92 , style="text-align:right" , 149 , 241.06031(5) , ~40 min , β , Np , 7/2+# , , --> , -id=Uranium-242 , U , , style="text-align:right" , 92 , style="text-align:right" , 150 , 242.06296(10) , 16.8(5) min , β , Np , 0+ , ,

Actinides vs fission products

Uranium-214

Uranium-214 is the lightest known isotope of uranium. It was discovered at the Spectrometer for Heavy Atoms and Nuclear Structure (SHANS) at the Heavy Ion Research Facility in Lanzhou,

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

in 2021, produced by firing argon-36 at tungsten-182. It alpha-decays with a half-life of .

Uranium-232

Uranium-232 has a half-life of 68.9 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using U, because the intense gamma radiation from Tl (a daughter of U, produced relatively quickly) makes U contaminated with it more difficult to handle. Uranium-232 is a rare example of an even-even isotope that is fissile with both thermal and fast neutrons.

Uranium-233

Uranium-233 is a fissile isotope that is bred from thorium-232 as part of the thorium fuel cycle. U was investigated for use in nuclear weapons and as a reactor fuel. It was occasionally tested but never deployed in nuclear weapons and has not been used commercially as a nuclear fuel. It has been used successfully in experimental nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of around 160,000 years. Uranium-233 is produced by neutron irradiation of thorium-232. When thorium-232 absorbs a

, it becomes thorium-233, which has a half-life of only 22 minutes. Thorium-233

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 ...

s into protactinium-233. Protactinium-233 has a half-life of 27 days and beta decays into uranium-233; some proposed molten salt reactor designs attempt to physically isolate the protactinium from further neutron capture before beta decay can occur. Uranium-233 usually fissions on neutron absorption but sometimes retains the neutron, becoming uranium-234. The capture-to-fission ratio is smaller than the other two major fissile fuels, uranium-235 and plutonium-239; it is also lower than that of short-lived plutonium-241, but bested by very difficult-to-produce neptunium-236.

Uranium-234

U occurs in natural uranium as an indirect decay product of uranium-238, but makes up only 55 parts per million of the uranium because its

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 245,500 years is only about 1/18,000 that of U. The path of production of U is this: U

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 ...

s to thorium-234. Next, with a short

, Th

s to protactinium-234. Finally, Pa beta decays to U. U

s to thorium-230, except for a small percentage of nuclei that undergo spontaneous fission. Extraction of small amounts of U from natural uranium could be done using isotope separation, similar to normal uranium-enrichment. However, there is no real demand in

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

, or engineering for isolating U. Very small pure samples of U can be extracted via the chemical ion-exchange process, from samples of plutonium-238 that have aged somewhat to allow some alpha decay to U. Enriched uranium contains more U than natural uranium as a byproduct of the uranium enrichment process aimed at obtaining uranium-235, which concentrates lighter isotopes even more strongly than it does U. The increased percentage of U in enriched natural uranium is acceptable in current nuclear reactors, but (re-enriched) reprocessed uranium might contain even higher fractions of U, which is undesirable. This is because U is not fissile, and tends to absorb slow neutrons in a

—becoming U. U has a

cross section of about 100 barns for thermal neutrons, and about 700 barns for its resonance integral—the average over neutrons having various intermediate energies. In a nuclear reactor, non-fissile isotopes capture a neutron breeding fissile isotopes. U is converted to U more easily and therefore at a greater rate than uranium-238 is to plutonium-239 (via neptunium-239), because U has a much smaller neutron-capture cross section of just 2.7 barns.

Uranium-235

Uranium-235 makes up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a fission chain reaction. It is the only fissile isotope that is a primordial nuclide or found in significant quantity in nature. Uranium-235 has a

of 703.8

million years Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used ...

. It was discovered in 1935 by Arthur Jeffrey Dempster. Its (fission) nuclear cross section for slow thermal neutron is about 504.81 barns. For fast neutrons it is on the order of 1 barn. At thermal energy levels, about 5 of 6 neutron absorptions result in fission and 1 of 6 result in neutron capture forming uranium-236. The fission-to-capture ratio improves for faster neutrons.

Uranium-236

Uranium-236 has a half-life of about 23 million years; and is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived

radioactive 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 ...

. It is found in spent

nuclear fuel Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other atomic nucleus, nuclear devices to generate energy. Oxide fuel For fission reactors, the fuel (typically based on uranium) is ...

and in the reprocessed uranium made from spent nuclear fuel.

Uranium-237

Uranium-237 has a half-life of about 6.75 days. It decays into neptunium-237 by

. It was discovered by Japanese physicist Yoshio Nishina in 1940, who in a near-miss discovery, inferred the creation of element 93, but was unable to isolate the then-unknown element or measure its decay properties.

Uranium-238

Uranium-238 (U or U-238) is the most common

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

in nature. It is not fissile, but is fertile: it can capture a slow

and after two beta decays become fissile plutonium-239. Uranium-238 is fissionable by fast neutrons, but cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. Doppler broadening of U's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control. About 99.284% of natural uranium is uranium-238, which has a half-life of 1.41×10 seconds (4.468×10 years). Depleted uranium has an even higher concentration of U, and even low-enriched uranium (LEU) is still mostly U. Reprocessed uranium is also mainly U, with about as much uranium-235 as natural uranium, a comparable proportion of uranium-236, and much smaller amounts of other isotopes of uranium such as uranium-234, uranium-233, and uranium-232.

Uranium-239

Uranium-239 is usually produced by exposing U to neutron radiation in a nuclear reactor. U has a half-life of about 23.45 minutes and

s into neptunium-239, 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. Np then, with a half-life of about 2.356 days, beta-decays to plutonium-239.

Uranium-241

In 2023, in a paper published in ''

Physical Review Letters ''Physical Review Letters'' (''PRL''), established in 1958, is a peer-reviewed, scientific journal that is published 52 times per year by the American Physical Society. The journal is considered one of the most prestigious in the field of physics ...

'', a group of researchers based in South Korea reported that they had found uranium-241 in an experiment involving U+Pt multinucleon transfer reactions. Its half-life is about 40 minutes.

References

{{Authority control Uranium