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Uranium-238 (238U or U-238) is the most common
isotope Isotopes are two or more types of atoms that have the same atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of ...
of
uranium Uranium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

uranium
found in nature, with a relative abundance of 99%. Unlike
uranium-235 Uranium-235 (235U) is an Isotopes of uranium, 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 th ...

uranium-235
, it is non-fissile, which means it cannot sustain 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 Positive feedback (exacerbating feedback, self-reinforcing feedback) is a pro ...
in a
thermal-neutron reactor A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and stru ...
. However, it is
fissionable In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutron The neutron is a subatomic particle, symbol or , which ha ...
by
fast neutrons The neutron detection temperature, also called the neutron energy, indicates a free neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a ...
, and is ''fertile'', meaning it can be transmuted to fissile
plutonium-239 Plutonium-239 (239Pu, Pu-239) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but differe ...

plutonium-239
. 238U cannot support a chain reaction because
inelastic scatteringIn chemistry, nuclear physics, and particle physics, inelastic scattering is a fundamental scattering process in which the kinetic energy of an incident particle is not conserved (in contrast to elastic scattering). In an inelastic scattering process ...
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 Neutron moderator, moderated ...
below the range where
fast fission Fast fission is nuclear fission, fission that occurs when a heavy atom absorbs a high-energy neutron, called a fast neutron, and splits. Most fissionable materials need thermal neutrons, which move more slowly. Fast reactors vs. thermal reactors Fa ...
of one or more next-generation nuclei is probable.
Doppler broadening In atomic physics, Doppler broadening is the broadening of spectral lines due to the Doppler effect caused by a distribution of velocities of atoms or molecules. Different velocities of the Spontaneous_emission, emitting particles result in differen ...
of 238U's
neutron absorption Neutron capture is a nuclear reaction In nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Other forms of nuclear matter are also studied. Nuclear physics should not ...
resonance Resonance describes the phenomenon of increased amplitude The amplitude of a Periodic function, periodic Variable (mathematics), variable is a measure of its change in a single Period (mathematics), period (such as frequency, time or Wavelen ...

resonance
s, increasing absorption as fuel temperature increases, is also an essential
negative feedback AB is negative. Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether cau ...
mechanism for reactor control. Around 99.284% of
natural uranium Natural uranium (NU, Unat) refers to uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and ...
's mass is uranium-238, which has a half-life of 1.41
second The second (symbol: s, also abbreviated: sec) is the base unit of time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, th ...
s (4.468 years, or 4.468 billion years). Due to its natural abundance and half-life relative to other
radioactive element A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by ...
s, 238U produces ~40% of the radioactive heat produced within the Earth. The 238U
decay chain In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most Radionuclide, radioisotopes do not de ...
contributes 6
electron anti-neutrinos
electron anti-neutrinos
per 238U nucleus (1 per
beta decay In , beta decay (''β''-decay) is a type of in which a (fast energetic or ) is emitted from an , transforming the original to an of that nuclide. For example, beta decay of a transforms it into a by the emission of an electron accompanie ...

beta decay
), resulting in a large detectable
geoneutrinoA geoneutrino is a neutrino or antineutrino emitted in decay of radionuclide naturally occurring in the Earth. Neutrinos, the lightest of the known subatomic particles, lack measurable electromagnetic properties and interact only via the Weak interac ...
signal when decays occur within the Earth. The decay of 238U to daughter isotopes is extensively used in
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "di ...
, particularly for material older than ~ 1 million years.
Depleted uranium Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is ...
has an even higher concentration of the 238U isotope, and even
low-enriched uranium Enriched uranium is a type of uranium Uranium is a chemical element with the Symbol (chemistry), 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 ...
(LEU), while having a higher proportion of the
uranium-235 Uranium-235 (235U) is an Isotopes of uranium, 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 th ...

uranium-235
isotope (in comparison to depleted uranium), is still mostly 238U.
Reprocessed uraniumReprocessed 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 actually makes up the bulk of the ...
is also mainly 238U, with about as much
uranium-235 Uranium-235 (235U) is an Isotopes of uranium, 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 th ...

uranium-235
as natural uranium, a comparable proportion of
uranium-236 Uranium-236 (236U) is an isotope of uranium that is neither fissile In nuclear engineering, fissile material is material capable of sustaining a nuclear fission In nuclear physics Nuclear physics is the field of physics that studies a ...

uranium-236
, and much smaller amounts of other
isotopes of uranium Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay pro ...
such as
uranium-234 Uranium-234 (234U, U-234) is an isotope of uranium. In natural uranium Natural uranium (NU, Unat) refers to uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemist ...

uranium-234
,
uranium-233 Uranium-233 (233U) is a fissile In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, i ...

uranium-233
, and
uranium-232 Uranium-232 () is an isotope of uranium. It has a half-life of around 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 ...

uranium-232
.


Nuclear energy applications

In a fission
nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction 300px, A possible nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron">uranium-235.html" ;"ti ...

nuclear reactor
, uranium-238 can be used to generate
plutonium-239 Plutonium-239 (239Pu, Pu-239) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but differe ...

plutonium-239
, which itself can be used in a
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics Nucl ...
or as a nuclear-reactor fuel supply. In a typical nuclear reactor, up to one-third of the generated power comes from the fission of 239Pu, which is not supplied as a fuel to the reactor, but rather, produced from 238U. A certain amount of production of from is unavoidable wherever it is exposed to
neutron radiation Neutron radiation is a form of ionizing radiation Ionizing radiation (ionising radiation) consists of subatomic particles or electromagnetic waves that have sufficient energy to ionization, ionize atoms or molecules by detaching electrons from the ...
, however, depending on
burnup In nuclear power technology, burnup (also known as fuel utilization) is a measure of how much energy is extracted from a primary nuclear fuel source. It is measured as the fraction of fuel atoms that underwent fission in %FIMA (fissions per initia ...

burnup
and
neutron temperature The neutron detection temperature, also called the neutron energy, indicates a free neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a ...
, different shares of the are in turn converted to , which determines the "grade" of produced Plutonium from weapons grade through reactor grade to Plutonium so high in (usually used "recycled"
MOX fuel Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alter ...
which entered the reactor containing significant amounts of Plutonium) that it cannot be used in current reactors operating with a thermal neutron spectrum.


Breeder reactors

238U is not usable directly as
nuclear fuel Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of Fissile mate ...
, though it can produce energy via "fast" fission. In this process, a neutron that has a kinetic energy in excess of 1 
MeV In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
can cause the nucleus of 238U to split in two. Depending on design, this process can contribute some one to ten percent of all fission reactions in a reactor, but too few of the average 2.5 neutrons produced in each fission have enough speed to continue a chain reaction. 238U can be used as a source material for creating plutonium-239, which can in turn be used as nuclear fuel.
Breeder reactor A breeder reactor is a nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants ...
s carry out such a process of transmutation to convert the
fertile Fertility is the capability to produce offspring through reproduction following the onset of sexual maturity. The fertility rate is the average number of children born by a female during her lifetime and is quantified Demography, demographicall ...
isotope 238U into fissile 239Pu. It has been estimated that there is anywhere from 10,000 to five billion years worth of 238U for use in these
power plantsPower Station or The Power Station may refer to: * Power station, a facility for the generation of electricity Music * The Power Station (band), a 1980s supergroup ** The Power Station (album), ''The Power Station'' (album), a 1985 album by The Pow ...

power plants
. Breeder technology has been used in several experimental nuclear reactors. By December 2005, the only breeder reactor producing power was the 600-megawatt
BN-600 reactor A cutaway model of the reactor. The core, that is the nuclear fuel at the heart of the reactor has dimensions of 2 meters in height by 0.75 meters in diameter, similar to the BN-800 reactor. The BN-600 reactor is a sodium-cooled fast breeder re ...
at the
Beloyarsk Nuclear Power Station The Beloyarsk Nuclear Power Station (NPS; russian: Белоярская атомная электростанция им. И. В. Курчатова []) was the third of the Soviet Union, Soviet Union's nuclear plants. It is situated by Zarechny, ...
in Russia. Russia later built another unit, BN-800 reactor, BN-800, at the Beloyarsk Nuclear Power Station which became fully operational in November 2016. Also, Japan's Monju breeder reactor, which has been inoperative for most of the time since it was originally built in 1986, was ordered for decommissioning in 2016, after safety and design hazards were uncovered, with a completion date set for 2047. Both China and India have announced plans to build nuclear breeder reactors. The breeder reactor as its name implies creates even larger quantities of 239Pu or 233U than the fission nuclear reactor. The Clean And Environmentally Safe Advanced Reactor (CAESAR), a nuclear reactor concept that would use steam as a moderator to control
delayed neutronIn nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicle ...
s, will potentially be able to use 238U as fuel once the reactor is started with
Low-enriched uranium Enriched uranium is a type of uranium Uranium is a chemical element with the Symbol (chemistry), 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 ...
(LEU) fuel. This design is still in the early stages of development.


Radiation shielding

238U is also used as a
radiation shield Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an international organization ''International Organization'' is a quarterly pe ...
– its alpha radiation is easily stopped by the non-
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the small, dense region consisting of s and s ...

radioactive
casing of the shielding and the uranium's high
atomic weight Relative atomic mass (symbol: ''A'') or atomic weight is a dimensionless physical quantity A physical quantity is a physical property of a material or system that can be Quantification (science), quantified by measurement. A physical quantity ...
and high number of
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s are highly effective in absorbing
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, it ...
s and
x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Moti ...

x-ray
s. It is not as effective as ordinary water for stopping
fast neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. It is defined as th ...
s. Both metallic
depleted uranium Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is ...
and depleted
uranium dioxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 ...

uranium dioxide
are used for radiation shielding. Uranium is about five times better as a gamma ray shield than
lead Lead is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elements ...

lead
, so a shield with the same effectiveness can be packed into a thinner layer. DUCRETE, a concrete made with uranium dioxide aggregate instead of gravel, is being investigated as a material for
dry cask storage Image:Nuclear dry storage.jpg, Dry cask storage area Dry cask storage is a method of storing high-level radioactive waste, such as spent nuclear fuel that has already been cooled in the spent fuel pool for at least one year and often as much as ten ...
systems to store
radioactive waste Radioactive waste is a type of hazardous waste Hazardous waste is waste Waste (or wastes) are unwanted or unusable materials. Waste is any substance which is discarded after primary use, or is worthless, defective and of no use. A by-pro ...
.


Downblending

The opposite of enriching is downblending. Surplus
highly enriched uranium Enriched uranium is a type of uranium Uranium is a chemical element with the Symbol (chemistry), 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 ...
can be downblended with depleted uranium or natural uranium to turn it into low-enriched uranium suitable for use in commercial nuclear fuel. 238U from depleted uranium and natural uranium is also used with recycled 239Pu from nuclear weapons stockpiles for making mixed oxide fuel (MOX), which is now being redirected to become fuel for nuclear reactors. This dilution, also called downblending, means that any nation or group that acquired the finished fuel would have to repeat the very expensive and complex chemical separation of uranium and plutonium process before assembling a weapon.


Nuclear weapons

Most modern
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics Nucl ...
s utilize 238U as a "tamper" material (see
nuclear weapon design Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as a ...
). A tamper which surrounds a fissile core works to reflect neutrons and to add
inertia Inertia is the resistance of any physical object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Entity, something that is tangible and within the grasp of the senses ** Object (abstract), an ob ...

inertia
to the compression of the 239Pu charge. As such, it increases the efficiency of the weapon and reduces the
critical mass In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, v ...
required. In the case of a
thermonuclear weapon A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon ...
, 238U can be used to encase the fusion fuel, the high flux of very energetic
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

neutron
s from the resulting
fusion
fusion
reaction causes 238U nuclei to split and adds more energy to the "yield" of the weapon. Such weapons are referred to as '' fission-fusion-fission'' weapons after the order in which each reaction takes place. An example of such a weapon is
Castle Bravo Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of ''Operation Castle''. Detonated on March 1, 1954, the device was the most powerful n ...
. The larger portion of the total explosive yield in this design comes from the final fission stage fueled by 238U, producing enormous amounts of radioactive
fission product Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium Uranium is a chemical element with the Symbol (chemistry), symbol U and atomic numbe ...
s. For example, an estimated 77% of the 10.4- megaton yield of the
Ivy Mike Ivy Mike was the codename given to the first full-scale test of a thermonuclear device, in which part of the explosive yield comes from nuclear fusion 400 px, The nuclear binding energy curve. The formation of nuclei with masses up to iron ...
thermonuclear test in 1952 came from fast fission of the depleted uranium
tamper Tamper may refer to: *Tamper, to use a tamp A tamp is a device used to compact or flatten an Aggregate (composite), aggregate or another powdered or granular material, typically to make it resistant to further compression or simply to increase it ...
. Because depleted uranium has no critical mass, it can be added to thermonuclear bombs in almost unlimited quantity. The
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a that spanned during its existence from 1922 to 1991. It was nominally a of multiple national ; in practice and were highly until its final years. The ...
's test of the
Tsar Bomba The Tsar Bomba (), (code name: ''Ivan'' or ''Vanya''), also known by the alphanumerical designation AN602, was a hydrogen bomb, hydrogen aerial bomb, and the most powerful nuclear weapon ever created and tested. Tsar Bomba was developed in the ...
in 1961 produced "only" 50 megatons of explosive power, over 90% of which came from fission caused by fusion-supplied neutrons, because the 238U final stage had been replaced with lead. Had 238U been used instead, the yield of the Tsar Bomba could have been well above 100 megatons, and it would have produced
nuclear fallout Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast Nuclear Blast is an independent record label and mail order record distributor with subsidiaries in Germany, the United St ...
equivalent to one third of the global total that had been produced up to that time.


Radium series (or uranium series)

The
decay chain In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most Radionuclide, radioisotopes do not de ...
of 238U is commonly called the "
radium series In nuclear science Nuclear physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, it ...
" (sometimes "uranium series"). Beginning with naturally occurring uranium-238, this series includes the following elements:
astatine Astatine is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavi ...

astatine
,
bismuth Bismuth is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that c ...

bismuth
,
lead Lead is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elements ...

lead
,
polonium Polonium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

polonium
,
protactinium Protactinium (formerly protoactinium) is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemic ...

protactinium
,
radium Radium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

radium
,
radon Radon is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that c ...

radon
,
thallium Thallium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

thallium
, and
thorium Thorium is a weakly radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the sma ...

thorium
. All of the
decay product In nuclear physics Nuclear physics is the field of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and ...
s are present, at least transiently, in any uranium-containing sample, whether metal, compound, or mineral. The decay proceeds as: :\begin\\ \ce \begin \ce \\ \ce \end \ce \\ \ce \end The
mean lifetime Image:Plot-exponential-decay.svg, upright=1.5, A quantity undergoing exponential decay. Larger decay constants make the quantity vanish much more rapidly. This plot shows decay for decay constant (λ) of 25, 5, 1, 1/5, and 1/25 for x from 0 to 5. A ...
of 238U is 1.41 seconds divided by 0.693 (or multiplied by 1.443), i.e. ca. 2 seconds, so 1
mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpidae ...
of 238U emits 3 alpha particles per second, producing the same number of thorium-234
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of ato ...

atom
s. In a closed system an equilibrium would be reached, with all amounts except for lead-206 and 238U in fixed ratios, in slowly decreasing amounts. The amount of 206Pb will increase accordingly while that of 238U decreases; all steps in the decay chain have this same rate of 3 decayed particles per second per mole 238U. Thorium-234 has a mean lifetime of 3 seconds, so there is equilibrium if one mole of 238U contains 9 atoms of thorium-234, which is 1.5 mole (the ratio of the two half-lives). Similarly, in an equilibrium in a closed system the amount of each decay product, except the end product lead, is proportional to its half-life. While 238U is minimally radioactive, its decay products, thorium-234 and protactinium-234, are
beta particle A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β ...
emitters with
half-lives Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics Nuclear physics is the field of physics Physics is the natural science that studies ...
of about 20 days and one minute respectively. Protactinium-234 decays to uranium-234, which has a half-life of hundreds of millennia, and this
isotope Isotopes are two or more types of atoms that have the same atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of ...
does not reach an equilibrium concentration for a very long time. When the two first isotopes in the decay chain reach their relatively small equilibrium concentrations, a sample of initially pure 238U will emit three times the radiation due to 238U itself, and most of this radiation is beta particles. As already touched upon above, when starting with pure 238U, within a human timescale the equilibrium applies for the first three steps in the decay chain only. Thus, for one mole of 238U, 3 times per second one alpha and two beta particles and a gamma ray are produced, together 6.7 MeV, a rate of 3 µW. Extrapolated over 2 seconds this is 600 gigajoules, the total energy released in the first three steps in the decay chain.


Radioactive dating

238U abundance and its decay to daughter isotopes comprises multiple "uranium dating" techniques and is one of the most common radioactive isotopes used in
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "di ...
. The most common dating method is uranium-lead dating, which is used to date rocks older than 1 million years old and has provided ages for the oldest rocks on Earth at 4.4 billion years old. The relation between 238U and 234U gives an indication of the age of
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
s and seawater that are between 100,000 years and 1,200,000 years in age. The 238U daughter product, 206Pb, is an integral part of
lead–lead datingLead–lead dating is a Chronological dating, method for dating geological samples, normally based on 'whole-rock' samples of material such as granite. For most dating requirements it has been superseded by uranium–lead dating (U–Pb dating), but ...
, which is most famous for the determination of the
age of the Earth The age of Earth is estimated to be 4.54 ± 0.05 billion A billion is a number with two distinct definitions: *1,000,000,000 1,000,000,000 (one billion A billion is a number with two distinct definitions: *1,000,000,000 1,000,000,00 ...
. The
Voyager program The Voyager program is an ongoing American scientific program that employs two robotic interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to Flyby ...
spacecraft carry small amounts of initially pure 238U on the covers of their
golden records Golden Records was a Simon & Schuster record label based in New York City. It was conceived and founded in 1948 by the Grammy Award-winning children's music producer, Arthur Shimkin, then a new recruit in the S&S business department. Shimkin we ...

golden records
to facilitate dating in the same manner.


Health concerns

Uranium emits
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proto ...

alpha particle
s through the process of
alpha decay
alpha decay
. External exposure has limited effect. Significant internal exposure to tiny particles of uranium or its decay products, such as thorium-230, radium-226 and radon-222 can cause severe health effects, such as cancer of the bone or liver. Uranium is also a toxic chemical, meaning that ingestion of uranium can cause kidney damage from its chemical properties much sooner than its radioactive properties would cause cancers of the bone or liver.''Uranium Mining in Virginia: Scientific, Technical, Environmental, Human Health and Safety, and Regulatory Aspects of Uranium Mining and Processing in Virginia''
Ch. 5. ''Potential Human Health Effects of Uranium Mining, Processing, and Reclamation''. National Academies Press (US); 2011 Dec 19.


See also

*
Depleted uranium Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium Uranium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is ...
* Uranium-lead dating


References


External links


NLM Hazardous Substances Databank – Uranium, Radioactive
{{Isotopes of uranium Actinides Fertile materials Isotopes of uranium Uranium Radionuclides used in radiometric dating