Isotope separation
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 fission weapons from plutonium, is generally agreed to be impractical.
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.
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 through a membrane, whose pore diameters are not larger than the mean free path length (Knudsen flow).
[4] The Paducah Gaseous Diffusion Plant was a US government effort to generate highly enriched uranium to power military reactors and create nuclear bombs which led to the establishment of the facility in 1952.
The goal of Paducah and its sister facility in Piketon was adjusted in the 1960s when they started to enrich uranium for use in commercial nuclear reactors to produce energy.
[5] Centrifugal schemes rapidly rotate the material allowing the heavier isotopes to go closer to an outer radial wall.
In modern times it is the main method used throughout the world to enrich uranium and as a result remains a fairly secretive process, hindering a more widespread uptake of the technology.
[9] Use of gaseous centrifugal technology to enrich isotopes is desirable as power consumption is greatly reduced when compared to more conventional techniques such as diffusion plants since fewer cascade steps are required to reach similar degrees of separation.
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.
[10] The method is simple because vortex tubes have no moving parts, but energy intensive, about 50 times greater than gas centrifuges.
At Oak Ridge National Laboratory and at the University of California, Berkeley, Ernest O. Lawrence developed electromagnetic separation for much of the uranium used in the first atomic bombs.
Its main eventual contribution to the war effort was to further concentrate material from the gaseous diffusion plants to higher levels of purity.
[13][14] 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.
A second laser, either also in the IR (infrared multiphoton dissociation) or in the UV, frees a fluorine atom, leaving uranium pentafluoride which then precipitates out of the gas.
But due to the small absorption probability in the overtones, too many photons remain unused, so that the method did not reach industrial feasibility.
For uranium, it uses a cold molecular beam with UF6 in a carrier gas, in which the 235UF6 is selectively excited by an infrared laser near 16 μm.
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 tritiated formate anions to HTO were measured as: Isotopes of hydrogen, carbon, oxygen, and nitrogen can be enriched by distilling suitable light compounds over long columns.
Deuterium enrichment by water distillation is only done, if it was preenriched by a process (chemical exchange) with lower energy demand.
Radioactive beams of specific isotopes are widely used in the fields of experimental physics, biology and materials science.
The production and formation of these radioactive atoms into an ionic beam for study is an entire field of research carried out at many laboratories throughout the world.
Arguably the principal Isotope Separator On Line (ISOL) is ISOLDE at CERN,[21] which is a joint European facility spread across the Franco-Swiss border near the city of Geneva.
This laboratory uses mainly proton spallation of uranium carbide targets to produce a wide range of radioactive fission fragments that are not found naturally on earth.
During spallation (bombardment with high energy protons), a uranium carbide target is heated to several thousand degrees so that radioactive atoms produced in the nuclear reaction are released.
Refractory metals such as tungsten and rhenium do not emerge from the target even at high temperatures due to their low vapour pressure.
The Ion Guide Isotope Separator On Line (IGISOL) technique was developed in 1981 at the University of Jyväskylä cyclotron laboratory in Finland.
This method of production and extraction takes place on a shorter timescale compared to the standard ISOL technique and isotopes with short half-lives (sub millisecond) can be studied using an IGISOL.
An IGISOL has also been combined with a laser ion source at the Leuven Isotope Separator On Line (LISOL) in Belgium.
This technique is used, for example, at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University and at the Radioactive Isotope Beam Factory (RIBF) at RIKEN, in Japan.
