Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes, for example separating natural uranium into enriched uranium and depleted uranium. This is the crucial process in the creation of a nuclear weapon. Isotopes are forms of an element whose nuclei have the same atomic number–-the number of protons in the nucleus--but different atomic masses because they contain different numbers of neutrons. ... A chemical element, often called simply element, is a chemical substance that cannot be divided or changed into other chemical substances by any ordinary chemical technique. ... Natural uranium (NU) refers to refined uranium with the same isotopic ratios as found in nature. ... Enriched uranium is uranium whose uranium-235 content has been increased through the process of isotope separation. ... // Depleted uranium (DU) is uranium which contains a reduced proportion of the fissile isotope U-235. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the hypocenter. ...

While in general chemical elements can be purified through chemical processes, isotopes of the same element have nearly identical chemical properties, which makes this type of separation impractical, except for separation of deuterium. A chemical reaction is a process that results in the interconversion of Chemical substances . ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance of one atom in 6500 of hydrogen. ...

There are three types of isotope separation techniques:

• Those based directly on the atomic weight of the isotope.
• Those based on the small differences in chemical reaction rates produced by different atomic weights.
• Those based on properties not directly connected to atomic weight, such as nuclear resonances.

The third type of separation is still experimental, practical separation techniques all depending in some way on the atomic mass. It is therefore generally easier to separate isotopes with a larger relative mass difference. For example deuterium has twice the mass of ordinary (light) hydrogen and it is generally easier to purify it than to separate Uranium-235 from the more common Uranium-238. On the other extreme, separation of fissile Plutonium-239 from the common impurity Plutonium-240, while desirable in that it would allow the creation of gun-type nuclear weapons from plutonium, is generally agreed to be impractical. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance of one atom in 6500 of hydrogen. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery gray metallic Atomic mass 238. ... General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery white Atomic mass (244) g/mol Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ...

See also: Enriched uranium

A LOAD OF NOTHING Enriched uranium is uranium whose uranium-235 content has been increased through the process of isotope separation. ...

Commercial materials

To date large-scale commercial isotope separation has occurred of only three elements. In each case, the rarer of the two most common isotopes of an element has been concentrated for use in nuclear technology:

• Uranium isotopes have been separated to prepare enriched uranium for use as nuclear reactor fuel and in nuclear weapons.
• Hydrogen isotopes have been separated to prepare heavy water for use as a moderator in nuclear reactors.
• Lithium-6 has been concentrated for use in thermonuclear weapons.

Isotope separation is an important process for both peaceful and military nuclear technology, and therefore the capability that a nation has for isotope separation is of extreme interest to the intelligence community. General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery gray metallic Atomic mass 238. ... Enriched uranium is uranium whose uranium-235 content has been increased through the process of isotope separation. ... Core of a nuclear reactor A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate (as opposed to a nuclear explosion, where the chain reaction occurs in a split second). ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the epicenter. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Heavy water is dideuterium oxide, or D2O or 2H2O. It is chemically the same as normal water, H2O, but the hydrogen atoms are of the heavy isotope deuterium, in which the nucleus contains a neutron in addition to the proton found in the nucleus of any hydrogen atom. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/gray Atomic mass 6. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, in 1945 lifted nuclear fallout some 18 km (60,000 feet) above the epicenter. ...

Alternatives

The only alternative to isotope separation is to manufacture the required isotope in its pure form. This may be done by irradiation of a suitable target, but care is needed in target selection and other factors to ensure that only the required isotope of the element of interest is produced. Isotopes of other elements are not so great a problem as they can be removed by chemical means.

This is particularly relevant in the preparation of high-grade plutonium-239 for use in weapons and in military propulsion reactors. It is not in practice possible to separate Pu-239 from Pu-240 or Pu-241. Fissile Pu-239 is produced following neutron capture by uranium-238, but further neutron capture will produce non-fissile Pu-240 and worse, then Pu-241 which is a fairly strong neutron emitter. Therefore, the uranium targets used to produce military plutonium must be irradiated for only a short time, to minimise the production of these unwanted isotopes. Conversely salting plutonium with Pu-241 renders it unsuitable for nuclear weapons. General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block ?, 7, f Appearance silvery white Atomic mass (244) g/mol Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ... This article or section should include material from Fissile material In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. ...

Techniques

Diffusion

Often done with gases, but also with liquids, the diffusion method relies on the fact that in thermal equilibrium, two isotopes with the same energy will have different average velocities. The lighter atoms (or the molecules containing them) will travel more quickly and be more likely to diffuse through a membrane. The difference in speeds is proportional to the square root of the mass ratio, so the amount of separation is small and many cascaded stages are needed to obtain high purity. This method is expensive due to the work needed to push gas through a membrane and the many stages necessary. Diffusion, being the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena. ...

The first large-scale separation of uranium isotopes was achieved by the United States in large gaseous diffusion separation plants at Oak Ridge Laboratories, which were established as part of the Manhattan Project. These used uranium hexafluoride gas as the process fluid, see gaseous diffusion. Oak Ridge National Laboratory (ORNL) is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle, LLC. ORNL is located in Oak Ridge, Tennessee, near Knoxville. ... Control panels and operators for calutrons at the Y-12 Plant in Oak Ridge, Tennessee. ... Uranium hexafluoride, or UF6, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. ... -1...

Centripetal effect

Centripetal effect schemes rapidly rotate the material allowing the heavier isotopes to go closer to an outer radial wall. This too is often done in gaseous form using a Zippe-type centrifuge. Centripetal force is the force pulling of an object toward the center of a circular path as the object goes around the circle. ... The Zippe-type centrifuge is a device designed to collect Uranium-235. ...

Gas centrifuges using uranium hexafluoride have largely replaced gaseous diffusion technology for uranium enrichment. As well as requiring less energy to achieve the same separation, far smaller scale plants are possible, making them an economic possibility for a small nation attempting to produce a nuclear weapon. Pakistan is believed to have used this method in developing its nuclear weapons. The gas centrifuge is a hyper-centrifuge used to produce enriched uranium. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the hypocenter. ...

Vortex tubes were used by South Africa in their Helikon Vortex Separation process. The gas is injected tangentially into a chamber with special geometry that further increases its rotation to a very high rate, causing the isotopes to separate. The method is simple because vortex tubes have no moving parts, but energy intensive (about 50 times greater than gas centrifuges). A similar process, known as Jet Nozzle, was created in Germany, with a demonstration plant built in Brazil, and they gone as far as developing a site to fuel the country's nuclear plants. The vortex tube, also known as the Ranque-Hilsch vortex tube, is a heat pump with no moving parts. ...

Electromagnetic

This method is a form of mass spectrometry, and is sometimes referred to by that name. It uses the fact that charged particles are deflected in a magnetic field and the amount of deflection depends upon the particle's mass. It is very expensive for the quantity produced, as it has an extremely low throughput, but it can allow very high purities to be achieved. This method is often used for processing small amounts of pure isotopes for research or specific use (such as isotopic tracers), but is impractical for industrial use. Mass spectrometry is an analytical technique which determines the mass-to-charge (m/z) ratio of ions. ... Current flowing through a wire produces a magnetic field (M) around the wire. ... An isotopic tracer, (also isotopic marker or isotopic label), is used in chemistry and biochemistry to help understand chemical reactions and interactions. ...

At Oak Ridge and at the University of California, Berkeley, Ernest O. Lawrence developed electromagnetic separation for much of the uranium used in the first United States atomic bomb (see Manhattan Project). Devices using his principle are named calutrons. After the war the method was largely abandoned as impractical. It had only been undertaken (along with diffusion and other technologies) to guarantee there would be enough material for use, whatever the cost. Its main eventual contribution to the war effort was to further concentrate material from the gaseous diffusion plants to even higher levels of purity. Oak Ridge is a city located in Anderson and Roane Counties in eastern Tennessee, about 25 miles west of Knoxville. ... University of California, Berkeley The University of California, Berkeley (also known as California, Cal, UCB, UC Berkeley, The University of California, or simply Berkeley) is a public coeducational university situated east of the San Francisco Bay in Berkeley, California, overlooking the Golden Gate. ... Ernest Orlando Lawrence (August 8, 1901 - August 27, 1958) was an American physicist and Nobel laureate best known for his invention of the cyclotron. ... Control panels and operators for calutrons at the Y-12 Plant in Oak Ridge, Tennessee. ... Schematic diagram of uranium isotope separation in the calutron. ...

Laser

In this method a laser is tuned to a wavelength which excites only one isotope of the material and ionizes those atoms preferentially. The resonant absorption of light for an isotope is dependent upon its mass and certain hyperfine interactions between electrons and the nucleus, allowing finely tuned lasers to only interact with one isotope. After the atom is ionized it can be removed from the sample by applying an electric field. This method is often abbreviated as AVLIS (atomic vapor laser isotope separation). This method has only recently been developed as laser technology has improved, and is currently not used extensively. However, it is a major concern to those in the field of nuclear proliferation because it may be cheaper and more easily hidden than other methods of isotope separation. The range of sizes in which lasers exist is immense, extending from microscopic diode lasers (top) to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion. ... In atomic physics, hyperfine structure is a small perturbation in the energy levels (or spectrum) of atoms or molecules due to the magnetic dipole-dipole interaction, arrising from the interaction of the nuclear magnetic dipole with the magnetic field of the electron. ... In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ... AVLIS Is an acronym which stands for atomic vapor laser isotope separation and is a method by which specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions. ... World map with nuclear weapons development status represented by color. ...

A second method of laser separation is known as MLIS, Molecular Laser Isotope Separation. In this method, an infrared laser is directed at uranium hexafluoride gas, exciting molecules that contain a U-235 atom. A second laser frees a fluorine atom, leaving uranium pentafluoride which then precipitates out of the gas. Cascading the MLIS stages is more difficult than with other methods because the UF₅ must be refluorinated (back to UF₆) before being introduced into the next MLIS stage. Alternative MLIS schemes are currently being developed (using a first laser in the near-infrared or visible region) where an enrichment of over 95% can be obtained in a single stage, but the methods have not (yet) reached industrial feasability. This method is called OP-IRMPD (Overtone Pre-excitation - IR Multiple Photon Dissociation). Molecular laser isotope separation (MLIS) is a method of isotope separation, where specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions of uranium hexafluoride molecules. ... Uranium hexafluoride, or UF6, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. ... Uranium-235 is an isotope of uranium that differs from the elements other common isotope, uranium-238, by its ability to cause a rapidly expanding fission chain reaction. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance pale greenish-yellow gas Atomic mass 18. ... Infrared multiphoton dissociation (IRMPD) is a technique used in mass spectrometry to fragment molecules in the gas phase usually for structural anaylsis of the original (parent) molecule. ...

Chemical methods

Although isotopes of a single element are normally described as having the same chemical properties, this is not strictly true. In particular, reaction rates are very slightly affected by atomic mass. The reaction rate for a reactant or product in a particular reaction is defined as the amount (in moles or mass units) per unit time per unit volume that is formed or removed. ...

Techniques using this are most effective for light atoms such as hydrogen. Lighter isotopes tend to react or evaporate more quickly than heavy isotopes, allowing them to be separated. This is how heavy water is produced commercially, see Girdler sulfide process for details. Lighter isotopes also disassociate more rapidly under an electric field. This process in a large cascade was used at the heavy water production plant at Rjukan. Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... Heavy water is dideuterium oxide, or D2O or 2H2O. It is chemically the same as normal water, H2O, but the hydrogen atoms are of the heavy isotope deuterium, in which the nucleus contains a neutron in addition to the proton found in the nucleus of any hydrogen atom. ... The Girdler Sulfide process is an industrial production method for making heavy water (dideuterium oxide), an important component of many nuclear reactors because it acts as a neutron moderator. ... A cascade is a term for a waterfall, or series of waterfalls, and is applied abstractly to many different concepts involving a series of steps or effects that follow one after the other. ... Map showing the position of Rjukan between lakes Møsvatn (West, upstream) and Tinnsjø (East) Rjukan is the centre of Tinn municipality in Telemark, Norway. ...

One candidate for the largest kinetic isotopic effect ever measured at room temperature, 305, may eventually be used for the separation of tritium (T). The effects for the oxidation of triated formate anions to HTO were measured as: The kinetic isotope effect is a difference in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes. ... Tritium (symbol T or 3H) is a radioactive isotope of hydrogen. ...

The SWU (separative work unit)

Separative Work Unit (SWU) is a complex unit which is a function of the amount of uranium processed and the degree to which it is enriched, ie the extent of increase in the concentration of the U-235 isotope relative to the remainder.

The unit is strictly: Kilogram Separative Work Unit, and it measures the quantity of separative work (indicative of energy used in enrichment) when feed and product quantities are expressed in kilograms. The effort expended in separating a mass F of feed of assay xf into a mass P of product assay xp and waste of mass W and assay xw is expressed in terms of the number of separative work units needed, given by the expression SWU = WV(xw) + PV(xp) - FV(xf), where V(x) is the "value function," defined as V(x) = (1 - 2x) ln((1 - x)/x).

Separative work is expressed in SWUs, kg SW, or kg UTA (from the German Urantrennarbeit )

• 1 SWU = 1 kg SW = 1 kg UTA
• 1 kSWU = 1.0 tSW = 1 t UTA
• 1 MSWU = 1 ktSW = 1 kt UTA

If, for example, you begin with 100 kilograms (220 pounds) of natural uranium, it takes about 60 SWU to produce 10 kilograms (22 pounds) of uranium enriched in U-235 content to 4.5%

External links

• Utilization of kinetic isotope effects for the concentration of tritium, GM Brown, TJ Meyer et al, 2001.
• Uranium Production
• Uranium Enrichment from the Uranium Information Centre Ltd