Neutron irradiation of uranium

J. Bloch, Effect of neutron irradiation of uranium-iron alloys dilute in iron, J. Nuclear Mater. 6 (1962) 203-212. 

Fermi enlisted the services of Italian chemist Oscar D Agostino. By neutron irradiation of uranium they found a new beta-emitting source, which D Agostino showed was none of the known elements between uranium (atomic number 92) and lead (atomic number 82). In 1934 Fermi reported the possibility that the atomic number of the element may be greater than 92 . He was cautious in voicing his conclusions, but could not resist naming the two new elements... 

Fujii, T., Yamana, H., Watanabe, M., Moriyama, H. 2002. Extraction study for TRUEX process using short-lived radionuclides produced by neutron irradiation of uranium. Solvent Extraction and Ion Exchange 20(2) 151-175. 

The most important method of production of the first transuranium elements is neutron irradiation of uranium. After the discovery of the neutron by Chadwick in 1932, this method was applied since 1934 by Fermi in Italy and by Hahn in Berlin. The method is based on the concept that absorption of neutrons by nuclides with atomic number Z leads to formation of neutron-rich nuclides that change by fi decay into nuclides with atomic numbers Z - -1. Unexpectedly, the experiments carried out by Hahn and Strassmann led to the discovery of nuclear fission in 1938. 

But rationalization is a way of surviving, too, and Meitner may have understood this. She and Hahn remained friends and correspondents until their deaths, months apart, when they were in their nineties. Recently though, Meitner s contribution has received some acknowledgment. The museum in Munich that displays the apparatus she designed for the neutron irradiation of uranium has changed the plaque from Worktable of Otto Hahn to Worktable of Otto Hahn, Lise Meitner, and Fritz Strassmann. ... 

Another major turning point in the history of nuclear science came with the discovery of fission by Otto Hahn and Fritz Strassmann in December 1938 (Hahn and Strassmann 1939a, b). In several laboratories in Rome, Berlin, and Paris, a complex series of P-decay chains resulting from neutron irradiation of uranium had been investigated since 1934, and these chains had been assigned to putative transuranium elements formed by neutron capture in uranium with subsequent P" transitions increasing the atomic numbers (see Sect. 1.2.3). But then evidence appeared that known elements in the vicinity of uranium, such as radium, were produced as well. When Hahn and Strassmaim attempted to prove this by a classical fractional crystallization separation of radium from barium serving as its carrier, the radioactivity turned out to be barium, not radium hence, new and totally unexpected type of nuclear reaction had to be invoked. 

Extension of the periodic table beyond uranium by the transmutation of elements was first attempted by neutron irradiation of uranium. Because neutron capture reactions in heavy... 

Nuclear reactions and decays occurring by neutron irradiation of uranium. Numbers along the decay paths a, i, IT) are half-lives (where m is for minute). Numbers along reaction paths ((n.y), fission) are cross sections (in barns) for a neutron spectrum of a standard-power light-water reactor, cross sections in parentheses are for thermal neutrons (0.025 eV). (The different arrows are explained by the insert in the lower right corner.) (Choppin and Rydberg 1980)... 

Ac and U are produced by the neutron irradiation of uranium-cycle by-products such Pa. 

Stimulated by the discovery of the neutron in 1932 by J. Chadwick and the first synthesis of artificial radioactive nuclei using a particle-induced nuclear reactions in 1934 by F. JoUot and I. Curie, many attempts were made to produce transuranium elements by neutron irradiation of uranium. In 1934, E. Fermi and later O. Hahn, L. Meitner, and F. Strassmann reported that they had created transuranium elements. But in 1938, O. Hahn and F. Strassmann showed that the radioactive species produced by neutron... 

Production in Target Elements. Tritium is produced on a large scale by neutron irradiation of Li. The principal U.S. site of production is the Savaimah River plant near Aiken, South Carolina where tritium is produced in large heavy-water moderated, uranium-fueled reactors. The tritium may be produced either as a primary product by placing target elements of Li—A1 alloy in the reactor, or as a secondary product by using Li—A1 elements as an absorber for control of the neutron flux. 

High-energy radiation may be classified into photon and particulate radiation. Gamma radiation is utilized for fundamental studies and for low-dose rate irradiations with deep penetration. Radioactive isotopes, particularly cobalt-60, produced by neutron irradiation of naturally occurring cobalt-59 in a nuclear reactor, and caesium-137, which is a fission product of uranium-235, are the main sources of gamma radiation. X-radiation, of lower energy, is produced by electron bombardment of suitable metal targets with electron beams, or in a... 

Among the long-lived isotopes of technetium, only Tc can be obtained in weigh-able amounts. It may be produced by either neutron irradiation of highly purified molybdenum or neutron-induced fission of uraniimi-235. The nuclides Tc and Tc are exclusively produced in traces by nuclear reations. Because of the high fission yield of more than 6%, appreciable quantities of technetimn-99 are isolated from uranium fission product mixtures. Nuclear reactors with a power of 100 MW produce about 2.5 g of Tc per day . 

This, in turn is produced by successive slow neutron irradiation of curium-244 Californium-254 may be produced by thermonuclear explosion resulting in the reaction of uranium-238 with intense neutron flux followed by a sequence of p- decays (Cunningham, B. B. 1968. In Encyclopedia of Chemical Elements, ed. Clifford A. Hampel, New York Reinhold Book Co.)... 

Plutonium-239 also is produced from natural uranium by the so-called pile reactions in which irradiation of uranium-235 isotope with neutrons produces fission, generating more neutrons and high energy ( 200 MeV). These neutrons are captured by the uranium-238 to yield plutonium-239. 

The final answer came from the atomic pile. J. A. Marinsky, L. E. Glendenin, and C. D. Coryell at the Clinton Laboratories at Oak Ridge (20) obtained a mixture of fission products of uranium which contained isotopes of yttrium and the entire group of rare earths from lanthanum through europium. Using a method of ion-exchange on Amberlite resin worked out by E. R. Tompkins, J. X. Khym, and W. E. Cohn (21) they were able to obtain a mixture of praseodymium, neodymium, and element 61, and to separate the latter by fractional elution from the Amberlite column with 5 per cent ammonium citrate at pH 2.75. Neutron irradiation of neodymium also produced 61. 

How would you know if you have made a new element Neutron irradiation of a small sample of uranium could be expected to produce only an extremely tiny amount of element 93, perhaps a thousand atoms or so. Because they are radioactive, such atoms should be easy to spot with a Geiger counter. But first you need to separate them from the uranium, which is radioactive too. This is why the nuclear physicists needed the help of chemists. From its beginning with the work of the Curies, nuclear chemistry or radiochemistry has had to work with incredibly tiny samples of rare elements, and has required a skill at analysis - separating substances into their elemental components - that Antoine Lavoisier could never have dreamed of. 

The uranium-graphite nuclear reactor (or nuclear pile ) was important not merely because it proved the feasibility of a self-sustaining fission chain. It could be used, with minor modification, for neutron irradiation of a sample by placing the sample in the interior of the reactor. Also, the system could be used as a source for the easily fissionable Pu239. This isotope (half-life 24,100 years) is a product in the decay chain from U239, which in turn results from the (n,y) reaction on U238 ... 

Although the fission products could be recovered as byproducts from the waste from spent nuclear reactor fuel, special-purpose neutron irradiation of highly enriched uranium (isotopically separated uranium-235) followed by chemical separation is the normal production method. The major products, molybdenum-99 and iodine-131 with fission yields of 6.1 and 6.7 percent, respectively, have important medical applications. Mo-99,... 

Fission of uranium was discovered by Hahn and Strassmann in their attempts to produce transuranium elements by irradiation of uranium with neutrons followed by p transmutation of the products. Instead of the expected transuranium elements they found radioactive products with appreciably lower atomic mass such as Ba, indicating the fission of the uranium nuclei. 

Tellurium formed by irradiation of uranium with thermal neutrons may have reacted with carbon monoxide to give carbon oxide telluride. ... 

Origins. Most of the radioactive waste at SRP originates in the two separations plants, although some waste is produced in the reactor areas, laboratories, and peripheral installations. The principal processes used in the separations plants have been the Purex and the HM processes, but others have been used to process a variety of fuel and target elements. The Purex process recovers and purifies uranium and plutonium from neutron-irradiated natural uranium. The HM process recovers enriched uranium from uranium—aluminum alloys used as fuel in SRP reactors. Other processes that have been used include recovery of and thorium (from neutron-irradiated thorium), recovery of Np and Pu, separation of higher actinide elements from irradiated plutonium, and recovery of enriched uranium from stainless-steel-clad fuel elements from power reactors. Each of these processes produces a characteristic waste. 

The lithium is in the form of an alloy with magnesium or aluminium which retains much of the tritium until it is released by treatment with acid. Alternatively the tritium can be produced by neutron irradiation of enriched LiF at 450° in a vacuum and then recovered from the gaseous products by diffusion through a palladium barrier. As a result of the massive production of tritium for thermonuclear devices and research into energy production by fusion reactions, tritium is available cheaply on the megacurie scale for peaceful purposes. The most convenient way of storing the gas is to react it with finely divided uranium... 

Pu. The isotope Pu results from neutron capture in followed by two beta decays. It is the principal isotopic constituent of plutonium formed by the irradiation of low-enrichment uranium. It is the principal flssile corrstituent in plutonium fuel used in thermal and fast reactors. Pu alpha decays, with a half-life of 24,400 years, to form the U parent of the An+3 decay series discussed in Chap. 5. Relatively pure Pu can be made by the short-term low-exposure inadiation of natural uranium. Plutonium containing more than 99 percent Pu results from the irradiation of uranium at fuel exposures of less than 0.7 MWd/kg [K2]. Because of the hi ... 

The isotope Cm is the largest contributor to the alpha activity of irradiated uranium fuel from power reactors. It is an important source of the 2n + 2 decay chain in the high4evel wastes from fuel reprocessing. The alpha activity of Cm results in an internal heat-generation rate of 120 W/g of pure Cm. Separated Cm, prepared by the neutron irradiation of Am, provides a useful alternative for a thermoelectric source and for radionuclide batteries when relatively high outputs are desired over short periods of the order of its half-Ufe of 163 days. For example, a space power generator denoted as SNAP-11 contained 7.5 g of Cm and produced 20 W of thermoelectric power. Cm is also the decay source of Pu, which is used as a longer-lived radioisotope heat source. 

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