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 Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

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 isotope In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...

uranium-238 Uranium-238 ( or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it i ...

and

uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...

, that have long

half-lives 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), a 2008 independent film by Jennifer Phang * '' Half Life: A Parable for t ...

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 In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps ( d ...

uranium-234 Uranium-234 ( or U-234) is an isotope of uranium. In natural uranium and in uranium ore, 234U occurs as an indirect decay product of uranium-238, but it makes up only 0.0055% (55 parts per million, or 1/18,000) of the raw uranium because its half ...

is also found. Other isotopes such as

uranium-233 Uranium-233 ( or U-233) is a fissile isotope of uranium that is bred from thorium-232 as part of the thorium fuel cycle. Uranium-233 was investigated for use in nuclear weapons and as a Nuclear fuel, reactor fuel. It has been used successfully ...

have been produced in

breeder reactor A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. These reactors can be fueled with more-commonly available isotopes of uranium and thorium, such as uranium-238 and thorium-232, as opposed to the ...

s. 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 The standard atomic weight of a chemical element (symbol ''A''r°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, ...

natural uranium Natural uranium (NU or Unat) is uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes from ura ...

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 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 ...

), U (0.7198–0.7202%), and U (0.0050–0.0059%). All three isotopes are

(i.e., they are

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), 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 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 produced ...

, decaying through the 18-member

uranium series In nuclear science a decay chain refers to the predictable series of radioactive disintegrations undergone by the nuclei of certain unstable chemical elements. Radioactive isotopes do not usually decay directly to stable isotopes, but rather ...

into

lead-206 Lead (82Pb) has four observationally stable isotopes: 204Pb, 206Pb, 207Pb, 208Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay ch ...

. 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 Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14.05 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its de ...

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 nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal Nuclear chain reaction#Fission chain reaction, chain reaction can only be achieved with fissil ...

in response to

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, 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 A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. Chain reactions are one way that sys ...

can be sustained with a large enough (

critical Critical or Critically may refer to: *Critical, or critical but stable, medical states **Critical, or intensive care medicine * Critical juncture, a discontinuous change studied in the social sciences. *Critical Software, a company specializing i ...

) mass of uranium-235. Uranium-238 is also important because it is

fertile Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate is ...

: it absorbs neutrons to produce a radioactive isotope that decays into

plutonium-239 Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main iso ...

, 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 dating Uranium–thorium dating, also called thorium-230 dating, uranium-series disequilibrium dating or uranium-series dating, is a radiometric dating technique established in the 1960s which has been used since the 1970s to determine the age of calcium ...

Used 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

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

radionuclide 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 ...

Used in

Uranium–lead dating Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routi ...

Important 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 Lanzhou is the capital and largest city of Gansu province in northwestern China. Located on the banks of the Yellow River, it is a key regional transportation hub, connecting areas further west by rail to the eastern half of the country. His ...

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 Nuclear proliferation is the spread of nuclear weapons to additional countries, particularly those not recognized as List of states with nuclear weapons, nuclear-weapon states by the Treaty on the Non-Proliferation of Nuclear Weapons, commonl ...

using U, because the intense

gamma radiation A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

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

with both thermal and fast neutrons.

Uranium-233

Uranium-233 is a fissile isotope that is bred from

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 (91Pa) has no stable isotopes. The four naturally occurring isotopes allow a standard atomic weight to be given. Thirty radioisotopes of protactinium have been characterized, ranging from 210Pa to 239Pa. The most stable isotope is 2 ...

. 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

. The capture-to-fission ratio is smaller than the other two major fissile fuels,

and

; it is also lower than that of short-lived

plutonium-241 Plutonium-241 ( or Pu-241) is an isotope of plutonium formed when plutonium-240 captures a neutron. Like some other plutonium isotopes (especially 239Pu), 241Pu is fissile, with a neutron absorption cross section about one-third greater than t ...

, but bested by very difficult-to-produce

neptunium-236 Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be syn ...

Uranium-234

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

million 1,000,000 (one million), or one thousand thousand, is the natural number following 999,999 and preceding 1,000,001. The word is derived from the early Italian ''millione'' (''milione'' in modern Italian), from ''mille'', "thousand", plus the ...

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 Thorium (90Th) has seven naturally occurring isotopes but none are stable. One isotope, 232Th, is ''relatively'' stable, with a half-life of 1.405×1010 years, considerably longer than the age of the Earth, and even slightly longer than the gen ...

. Next, with a short

, Th

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

s to

thorium-230 Thorium (90Th) has seven naturally occurring isotopes but none are stable. One isotope, 232Th, is ''relatively'' stable, with a half-life of 1.405×1010 years, considerably longer than the age of the Earth, and even slightly longer than the gen ...

, except for a small percentage of nuclei that undergo

spontaneous fission Spontaneous fission (SF) is a form of radioactive decay in which a heavy atomic nucleus splits into two or more lighter nuclei. In contrast to induced fission, there is no inciting particle to trigger the decay; it is a purely probabilistic proc ...

. Extraction of small amounts of U from natural uranium could be done using

isotope separation Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is varied. The largest variety is used in research (e.g. in chemistry where atoms of "marker" n ...

, 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 Plutonium-238 ( or Pu-238) is a radioactive isotope of plutonium that has a half-life of 87.7 years. Plutonium-238 is a very powerful alpha emitter; as alpha particles are easily blocked, this makes the plutonium-238 isotope suitable for usage ...

that have aged somewhat to allow some alpha decay to U.

Enriched uranium Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (23 ...

contains more U than natural uranium as a byproduct of the uranium enrichment process aimed at obtaining

, 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 Reprocessed uranium (RepU) is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium makes up the bulk of the material ...

might contain even higher fractions of U, which is undesirable. This is because U is not

, and tends to absorb slow

neutrons The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The neutron was discovered by James Chadwick in 1932, leading to the discovery of nuclear fission in 1938, the f ...

in a

—becoming U. U has a

cross section of about 100

barns 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. ...

for

thermal neutrons 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 ...

, and about 700 barns for its

resonance integral 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 ...

—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

is to

(via

neptunium-239 Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be ...

), because U has a much smaller neutron-capture

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 ...

of just 2.7 barns.

Uranium-235

Uranium-235 makes up about 0.72% of natural uranium. Unlike the predominant isotope

, it is

, i.e., it can sustain a fission

. It is the only fissile isotope that is a

primordial nuclide In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...

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 Arthur Jeffrey Dempster (August 14, 1886 – March 11, 1950) was a Canadian-American physicist best known for his work in mass spectrometry and his discovery in 1935 of the uranium isotope 235U. Early life and education Dempster was born in ...

. Its (fission) nuclear

for slow

is about 504.81

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 fast

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 Uranium-236 ( or U-236) is an isotope of uranium that is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in ...

. 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 Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be ...

. It was discovered by Japanese physicist

Yoshio Nishina was a Japanese physicist who was called "the founding father of modern physics research in Japan". He led the efforts of Japan to develop an atomic bomb during World War II. Early life and career Nishina was born in Satoshō, Okayama. He rece ...

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

, but is

: it can capture a slow

and after two beta decays become fissile

. Uranium-238 is fissionable by fast neutrons, but cannot support a chain reaction because inelastic scattering reduces

neutron energy 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 ...

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

, and

uranium-232 Uranium-232 () is an isotope of uranium. It has a half-life of around 69 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using 233U as the fissile material, because the intense gamma ...

Uranium-239

Uranium-239 is usually produced by exposing U to

neutron radiation Neutron radiation is a form of ionizing radiation that presents as free neutrons. Typical phenomena are nuclear fission or nuclear fusion causing the release of free neutrons, which then react with nuclei of other atoms to form new nuclides— ...

in a nuclear reactor. U has a half-life of about 23.45 minutes and

s into

, 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

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