Uranium-238
Encyclopedia
Uranium-238 is the most common isotope
of uranium
found in nature. It is not fissile
, but is a fertile material
: it can capture
a slow neutron
and after two beta decay
s become fissile plutonium-239
. 238U is fissionable by fast neutrons, but cannot support a chain reaction
because inelastic scattering
reduces neutron energy below the range where fast fission
is probable.
Around 99.284% of natural uranium
is uranium-238, which has a half-life of 1.41 second
s (4.468 years, or 4.468 billion years).
Depleted uranium
has an even higher concentration of the 238U isotope, and even low-enriched uranium, while having a higher proportion of the uranium-235
isotope, is still mostly 238U. Reprocessed uranium
is also mainly 238U, 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-238 can be used to breed Pu-239, which itself can be used in a nuclear weapon or as a nuclear-reactor fuel supply. In fact, in atypical nuclear reactor, up to one-third of the generated power does come from the fission of Pu-239, which is not supplied as a fuel to the reactor, but rather, produced
from 238U.
, though it can produce energy via "fast" fission. In this process, a neutron that has a kinetic energy in excess of 1 MeV 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 about 1.7 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
s carry out such a process of transmutation to convert the fertile
isotope 238U into fissile Pu-239. It has been estimated that there is anywhere from 10,000 to five billion years worth of 238U for use in these power plants
. Breeder technology has been used in several experimental nuclear reactors.
As of December 2005, the only breeder reactor producing power is the 600-megawatt BN-600 reactor
at the Beloyarsk Nuclear Power Station
in Russia
. Russia has planned to build another unit, BN-800, at the Beloyarsk nuclear power plant. Also, Japan
's Monju breeder reactor is planned to be started, having been shut down since 1995, and both China
and India
have announced plans to build nuclear breeder reactors.
The breeder reactor as its name implies creates even larger quantities of Pu-239 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 neutron
s, will potentially be able to burn 238U as fuel once the reactor is started with LEU fuel
. This design is still in the early stages of development.
and high number of electron
s are highly effective in absorbing gamma ray
s and x-ray
s. It is not as effective as ordinary water for stopping fast neutrons. Both metallic depleted uranium and depleted uranium dioxide
are used for radiation shielding. Uranium is about five times better as a gamma ray shield than 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
systems to store radioactive waste
.
.
238U from depleted uranium and natural uranium is also used with recycled Pu-239 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 enrichment and separation processes before assembling a weapon.
s utilize 238U as a "tamper" material (see nuclear weapon design
). A tamper which surrounds a fissile core works to reflect neutrons
and to add inertia
to the compression of the Pu-239 charge. As such, it increases the efficiency of the weapon and reduces the critical mass required. In the case of a thermonuclear weapon 238U
can be used to encase the fusion fuel, the high flux of very energetic neutron
s from the resulting 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 three consecutive stages of the explosion
. An example of such a weapon is Castle Bravo
although the fission of its unenriched uranium tamper was not intentional.
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
s. For example, an estimated 77% of the 10.4-megaton yield of the Ivy Mike
thermonuclear test in 1952 came from fast fission
of the depleted uranium tamper. Because depleted uranium has no critical mass, it can be added to thermonuclear bombs in almost unlimited quantity. The Soviet Union's
test of the "Tsar Bomba
" in 1961 produced "only" 60 megatons of explosive power, over 90% of which came from fusion, 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
equivalent to one third of the global total that had been produced up to that time.
and decays (by way of thorium
-234 and protactinium
-234) into uranium-234. 234U has a half-life
of 245,500 years. The relation between 238U and 234U gives an indication of the age of sediment
s that are between 100,000 years and 1,200,000 years in age.
238U occasionally decays by spontaneous fission
or double beta decay
with probabilities of 5 and 2 per 100 alpha decays, respectively.
-238, this series includes the following elements: astatine
, bismuth
, lead
, polonium
, protactinium
, radium
, radon
, thallium
, and thorium
. All are present, at least transiently, in any uranium-containing sample, whether metal, compound, or mineral.
The mean lifetime of 238U is 1.41 seconds divided by 0.693 (or multiplied by 1.443), i.e. ca. 2 seconds, so 1 mole
of 238U emits 3 alpha particles per second, producing the same number of thorium-234 (Th-234) 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 Pb-206 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.
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 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.
Isotopes of uranium
Uranium is a naturally occurring radioactive element that has no stable isotopes but two primordial isotopes that have long half-life and are found in appreciable quantity in the Earth's crust, along with the decay product uranium-234. The average atomic mass of natural uranium is 238.02891 u...
of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
found in nature. It is not fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...
, but is a fertile material
Fertile material
Fertile material is a term used to describe nuclides which generally themselves do not undergo induced fission but from which fissile material is generated by neutron absorption and subsequent nuclei conversions...
: it can capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...
a slow neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
and after two beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
s become fissile plutonium-239
Plutonium-239
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
. 238U is fissionable by fast neutrons, but cannot support a chain reaction
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....
because inelastic scattering
Inelastic scattering
In particle physics and chemistry, inelastic scattering is a fundamental scattering process in which the kinetic energy of an incident particle is not conserved . In an inelastic scattering process, some of the energy of the incident particle is lost or gained...
reduces neutron energy below the range where fast fission
Fast fission
Fast fission is 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 slower.-Fast reactors vs. thermal reactors:...
is probable.
Around 99.284% of natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...
is uranium-238, which has a half-life of 1.41 second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
s (4.468 years, or 4.468 billion years).
Depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...
has an even higher concentration of the 238U isotope, and even low-enriched uranium, while having a higher proportion of the uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
isotope, is still mostly 238U. Reprocessed uranium
Reprocessed uranium
Reprocessed uranium 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 material separated during reprocessing...
is also mainly 238U, with about as much uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
as natural uranium, a comparable proportion of uranium-236
Uranium-236
- See also :* Depleted uranium* Uranium market* Nuclear reprocessing* United States Enrichment Corporation* Nuclear fuel cycle* Nuclear power-External links:* *...
, and much smaller amounts of other isotopes of uranium such as uranium-234, uranium-233
Uranium-233
Uranium-233 is a fissile isotope of uranium, bred from Thorium as part of the thorium fuel cycle. It has been used in a few nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of 160,000 years....
, and uranium-232.
Nuclear energy applications
In a fission nuclear reactorNuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
, uranium-238 can be used to breed Pu-239, which itself can be used in a nuclear weapon or as a nuclear-reactor fuel supply. In fact, in a
Nuclear transmutation
Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of other element by 'transmutation'...
from 238U.
Breeder reactors
238U is not usable directly as nuclear fuelNuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...
, though it can produce energy via "fast" fission. In this process, a neutron that has a kinetic energy in excess of 1 MeV 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 about 1.7 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
Breeder reactor
A breeder reactor is a nuclear reactor capable of generating more fissile material than it consumes because its neutron economy is high enough to breed fissile from fertile material like uranium-238 or thorium-232. Breeders were at first considered superior because of their superior fuel economy...
s carry out such a process of transmutation to convert the fertile
Fertile material
Fertile material is a term used to describe nuclides which generally themselves do not undergo induced fission but from which fissile material is generated by neutron absorption and subsequent nuclei conversions...
isotope 238U into fissile Pu-239. It has been estimated that there is anywhere from 10,000 to five billion years worth of 238U for use in these power plants
Power station
A power station is an industrial facility for the generation of electric energy....
. Breeder technology has been used in several experimental nuclear reactors.
As of December 2005, the only breeder reactor producing power is the 600-megawatt BN-600 reactor
BN-600 reactor
The BN-600 reactor is a sodium-cooled fast breeder reactor, built at the Beloyarsk Nuclear Power Station, in Zarechny, Sverdlovsk Oblast, Russia. Designed to generate electrical power of 600 MW in total, the plant dispatches 560 MW to the Middle Urals power grid...
at the Beloyarsk Nuclear Power Station
Beloyarsk Nuclear Power Station
The Beloyarsk Nuclear Power Station , was the second of the then Soviet Union's nuclear plants. It is situated by Zarechny in Sverdlovsk Oblast, Russia. Zarechny township was created to service the station, which is named after the Beloyarsky District...
in Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. Russia has planned to build another unit, BN-800, at the Beloyarsk nuclear power plant. Also, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
's Monju breeder reactor is planned to be started, having been shut down since 1995, and both China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
have announced plans to build nuclear breeder reactors.
The breeder reactor as its name implies creates even larger quantities of Pu-239 than the fission nuclear reactor.
The Clean And Environmentally Safe Advanced Reactor
Clean And Environmentally Safe Advanced Reactor
The Clean And Environmentally Safe Advanced Reactor is a nuclear reactor concept that uses steam as a moderator. Steam's density can be controlled very finely so, according to its developer Dr...
(CAESAR), a nuclear reactor concept that would use steam as a moderator to control delayed neutron
Delayed neutron
In nuclear engineering, a delayed neutron is a neutron emitted after a nuclear fission event by one of the fission products anytime from a few milliseconds to a few minutes later....
s, will potentially be able to burn 238U as fuel once the reactor is started with LEU fuel
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...
. This design is still in the early stages of development.
Radiation shielding
238U is also used as a radiation shield — its alpha radiation is easily stopped by the non-radioactive casing of the shielding and the uranium's high atomic weightAtomic weight
Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12...
and high number of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s are highly effective in absorbing gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s and x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s. It is not as effective as ordinary water for stopping fast neutrons. Both metallic depleted uranium and depleted uranium dioxide
Uranium dioxide
Uranium dioxide or uranium oxide , also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used...
are used for radiation shielding. Uranium is about five times better as a gamma ray shield than lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, so a shield with the same effectiveness can be packed into a thinner layer.
DUCRETE
Ducrete
DUCRETE is a high density concrete alternative investigated for use in construction of casks for storage of radioactive waste...
, a concrete made with uranium dioxide aggregate
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...
instead of gravel, is being investigated as a material for dry cask storage
Dry cask storage
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.. These casks are typically steel cylinders that are either welded or bolted closed. When inside, the fuel rods are surrounded...
systems to store radioactive waste
Radioactive waste
Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...
.
Downblending
The opposite of enriching is downblending. Surplus highly-enriched uranium can be downblended with depleted uranium or natural uranium to turn it into low enriched uranium suitable for use in commercial nuclear fuelNuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...
.
238U from depleted uranium and natural uranium is also used with recycled Pu-239 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 enrichment and separation processes before assembling a weapon.
Nuclear weapons
Most modern nuclear weaponNuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s utilize 238U as a "tamper" material (see nuclear weapon design
Nuclear weapon design
Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three basic design types...
). A tamper which surrounds a fissile core works to reflect neutrons
Neutron reflector
A neutron reflector is any material that reflects neutrons. This refers to elastic scattering rather than to a specular reflection. The material may be graphite, beryllium, steel, and tungsten carbide, or other materials...
and to add inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
to the compression of the Pu-239 charge. As such, it increases the efficiency of the weapon and reduces the critical mass required. In the case of a thermonuclear weapon 238U
can be used to encase the fusion fuel, the high flux of very energetic neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s from the resulting fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
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 three consecutive stages of the explosion
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
. An example of such a weapon is Castle Bravo
Castle Bravo
Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,...
although the fission of its unenriched uranium tamper was not intentional.
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
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
s. For example, an estimated 77% of the 10.4-megaton yield of the Ivy Mike
Ivy Mike
Ivy Mike was the codename given to the first United States test of a thermonuclear weapon, in which a major part of the explosive yield came from nuclear fusion. It was detonated on November 1, 1952 by the United States at on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy...
thermonuclear test in 1952 came from fast fission
Fast fission
Fast fission is 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 slower.-Fast reactors vs. thermal reactors:...
of the depleted uranium tamper. Because depleted uranium has no critical mass, it can be added to thermonuclear bombs in almost unlimited quantity. The Soviet Union's
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
test of the "Tsar Bomba
Tsar Bomba
Tsar Bomba is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. It was also referred to as Kuz'kina Mat , in this usage meaning "something that has not been seen before"....
" in 1961 produced "only" 60 megatons of explosive power, over 90% of which came from fusion, 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
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
equivalent to one third of the global total that had been produced up to that time.
Radioactivity and decay
238U radiates alpha-particlesAlpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
and decays (by way of thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
-234 and protactinium
Protactinium
Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume...
-234) into uranium-234. 234U has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 245,500 years. The relation between 238U and 234U gives an indication of the age of sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s that are between 100,000 years and 1,200,000 years in age.
238U occasionally decays by spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
or double beta decay
Double beta decay
Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...
with probabilities of 5 and 2 per 100 alpha decays, respectively.
Radium series (or uranium series)
The 4n+2 chain of 238U is commonly called the "radium series" (sometimes "uranium series"). Beginning with naturally occurring uraniumUranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
-238, this series includes the following elements: astatine
Astatine
Astatine is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table...
, bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, polonium
Polonium
Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
, protactinium
Protactinium
Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume...
, radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
, radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...
, thallium
Thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray poor metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy...
, and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
. All are present, at least transiently, in any uranium-containing sample, whether metal, compound, or mineral.
| Nuclide | Historic name (short) | Historic name (long) | Decay mode | Half-life Half-life Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to... |
MeV | Decay product |
|---|---|---|---|---|---|---|
| 238U | U | Uranium | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
4.468·109 a Julian year (astronomy) In astronomy, a Julian year is a unit of measurement of time defined as exactly 365.25 days of 86 400 SI seconds each, totaling 31 557 600 seconds. The Julian year is the average length of the year in the Julian calendar used in Western societies in previous centuries, and for which the unit is... |
4.270 | 234Th |
| 234Th | UX1 | Uranium X1 | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
24.10 d Day A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun... |
0.273 | 234mPa |
| 234mPa | UX2 | Uranium X2 | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... 99.84 % IT Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer.... 0.16 % |
1.16 min Minute A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units... |
2.271 0.074 |
234U 234Pa |
| 234Pa | UZ | Uranium Z | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
6.70 h Hour The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds... |
2.197 | 234U |
| 234U | UII | Uranium two | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
245500 a | 4.859 | 230Th |
| 230Th | Io | Ionium | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
75380 a | 4.770 | 226Ra |
| 226Ra | Ra | Radium | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
1602 a | 4.871 | 222Rn |
| 222Rn | Rn | Radon | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
3.8235 d | 5.590 | 218Po |
| 218Po | RaA | Radium A | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... 99.98 % β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... 0.02 % |
3.10 min Minute A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units... |
6.115 0.265 |
214Pb 218At |
| 218At | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... 99.90 % β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... 0.10 % |
1.5 s Second The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock.... |
6.874 2.883 |
214Bi 218Rn |
||
| 218Rn | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
35 ms Millisecond A millisecond is a thousandth of a second.10 milliseconds are called a centisecond.... |
7.263 | 214Po | ||
| 214Pb | RaB | Radium B | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
26.8 min | 1.024 | 214Bi |
| 214Bi | RaC | Radium C | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... 99.98 % α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... 0.02 % |
19.9 min | 3.272 5.617 |
214Po 210Tl |
| 214Po | RaC' | Radium C' | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
0.1643 ms | 7.883 | 210Pb |
| 210Tl | RaC" | Radium C" | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
1.30 min | 5.484 | 210Pb |
| 210Pb | RaD | Radium D | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
22.3 a | 0.064 | 210Bi |
| 210Bi | RaE | Radium E | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... 99.99987% α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... 0.00013% |
5.013 d | 1.426 5.982 |
210Po 206Tl |
| 210Po | RaF | Radium F | α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... |
138.376 d | 5.407 | 206Pb |
| 206Tl | β- Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a... |
4.199 min | 1.533 | 206Pb | ||
| 206Pb | – | stable | – | – |
The mean lifetime of 238U is 1.41 seconds divided by 0.693 (or multiplied by 1.443), i.e. ca. 2 seconds, so 1 mole
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
of 238U emits 3 alpha particles per second, producing the same number of thorium-234 (Th-234) atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
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 Pb-206 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.
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 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.