Calutron
A calutron is a mass spectrometer originally designed and used for separating the isotopes of uranium. It was developed by Ernest Lawrence during the Manhattan Project and was based on his earlier invention, the cyclotron. Its name was derived from California University Cyclotron, in tribute to Lawrence's institution, the University of California, where it was invented. Calutrons were used in the industrial-scale Y-12 uranium enrichment plant at the Clinton Engineer Works in Oak Ridge, Tennessee. The enriched uranium produced was used in the Little Boy atomic bomb that was detonated over Hiroshima on 6 August 1945.
The calutron is a type of sector mass spectrometer, an instrument in which a sample is ionized and then accelerated by electric fields and deflected by magnetic fields. The ions ultimately collide with a plate and produce a measurable electric current. Since the ions of the different isotopes have the same electric charge but different masses, the heavier isotopes are deflected less by the magnetic field, causing the beam of particles to separate into several beams by mass, striking the plate at different locations. The mass of the ions can be calculated according to the strength of the field and the charge of the ions. During World War II, calutrons were developed to use this principle to obtain substantial quantities of high-purity uranium-235, by taking advantage of the small mass difference between uranium isotopes.
Electromagnetic separation for uranium enrichment was abandoned in the post-war period in favor of the more complicated, but more efficient, gaseous diffusion method. Although most of the calutrons of the Manhattan Project were dismantled at the end of the war, some remained in use to produce isotopically enriched samples of naturally occurring elements for military, scientific and medical purposes.
Postwar years[edit]
The workforce at Y-12 dropped from a wartime peak of 22,482 on 21 August 1945 to less than 1,700 in 1949.[69] All the calutrons were removed and dismantled, except for the XAX and XBX training tracks in Building 9731, and the Beta 3 racetracks in Building 9204–3.[90][91] In 1947, Eugene Wigner, the director of the Oak Ridge National Laboratory (ORNL), asked the Atomic Energy Commission for permission to use the Beta calutrons to produce isotopes for physics experiments. Permission was granted, and a wide range of isotopes was produced. Lithium-6 from the Beta calutrons was used for research into thermonuclear weapons. Many other isotopes were used for peaceful scientific and medical purposes.[92] The Beta 3 racetracks were transferred to the ORNL in March 1950.[91] By the mid-1950s, the Beta calutrons had produced quantities of all the naturally occurring stable isotopes except those of osmium, which had to wait until April 1960.[93] The calutrons continued to produce isotopes until 1998.[94] As of 2015, they are still on standby.[95]
Other countries[edit]
Soviet Union and China[edit]
Like the United States, the Soviet Union (USSR) carried out research on multiple enrichment technologies for the Soviet atomic bomb project. A trial electromagnetic process was carried out in 1946 with a calutron using a magnet taken from Germany. A site was chosen for an electromagnetic plant at Sverdlovsk-45 in 1946. The pilot plant, known as Plant 418, was completed in 1948. A more efficient design was developed in which the particle beams were bent by 225° instead of 180° as in the American calutron. It was used to complete the uranium enrichment process after technical difficulties were encountered with the gaseous diffusion process. Uranium enriched to about 40 percent uranium-235 was brought to Sverdlovsk-45 for final enrichment to between 92 and 98 percent. After the problems with the gaseous diffusion process were resolved in 1950, it was decided not to proceed with a full-scale electromagnetic plant.[96][97] As of 2009, it remains operational.[91] In 1969, a research calutron known as S-2 was built at Arzamas-16 for high-efficiency separation of isotopes of heavy elements like plutonium.[96][98][99]
Four research and production calutrons were built at the China Institute of Atomic Energy in Beijing of identical design to those of the USSR in the early 1960s.[100][101][102]
United Kingdom[edit]
In 1945, the British atomic bomb project built a 180° calutron, similar in design to an American Beta calutron, at the Atomic Energy Research Establishment at Harwell, Oxfordshire. Owing to the success of the gaseous diffusion plant at Capenhurst, electromagnetic separation was not pursued by the United Kingdom, and the calutron was used to separate isotopes for research. The 180° design was not ideal for this purpose, so Harwell built a 90° calutron, HERMES, the "Heavy Elements and Radioactive Material Electromagnetic Separator".[103] It was inspired by France's SIDONIE and PARIS separators at the Laboratoire René Bernas of the University of Paris IX in Orsay, and PARSIFAL at the military research laboratory of the Commissariat à l'énergie atomique et aux énergies alternatives in Bruyères-le-Châtel.[104][105]
Israel, Japan, and France[edit]
Israel, Japan and France also built some research calutrons, including the SOLIS and MEIRA separators at the Soreq Nuclear Research Center. There is also CERN's Isotope Separator On-Line Detector (ISOLDE), which was built in 1967.[106]
India[edit]
A calutron at the Saha Institute of Nuclear Physics at Bidhan Nagar in India was used to produce plutonium for India's first nuclear test on 18 May 1974.[96][107]
Iraq[edit]
After the 1990–91 Gulf War, UNSCOM determined that Iraq had been pursuing a calutron program to enrich uranium.[108] Iraq chose to develop the electromagnetic process over more modern, economic, and efficient methods of enrichment because calutrons were easier to build, with fewer technical challenges, and the components required to build them were not subject to export controls.[109][110] At the time the program was discovered, Iraq was estimated to be two or three years away from producing enough material for nuclear weapons. The program was destroyed in the Gulf War.[111] Consequently, the Nuclear Suppliers Group added the electromagnetic separation equipment to its guidelines for transfers of nuclear-related dual-use equipment, material and technology.[112][113]
