Uranium, neutron bombardment

The new elements neptunium and plutonium have been produced in quantity by neutron bombardment of uranium. Subsequently many isotopes have been obtained by transmutation and synthetic isotopes of elements such as Ac and Pa are more easily obtained than the naturally occurring species. Synthetic species of lighter elements, e.g. Tc and Pm are also prepared. 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

ThSiO "Th and Th are present in naturally occurring uranium Th and Th occur in uranium minerals as members of the decay chain. The remaining isotopes are formed upon neutron bombardment of those isotopes discussed, or by charged particle bombardment of various targets. 

In 1938 Niels Bohr had brought the astounding news from Europe that the radiochemists Otto Hahn and Fritz Strassmann in Berlin had conclusively demonstrated that one of the products of the bom-bardmeiit of uranium by neutrons was barium, with atomic number 56, in the middle of the periodic table of elements. He also announced that in Stockholm Lise Meitner and her nephew Otto Frisch had proposed a theory to explain what they called nuclear fission, the splitting of a uranium nucleus under neutron bombardment into two pieces, each with a mass roughly equal to half the mass of the uranium nucleus. The products of Fermi s neutron bombardment of uranium back in Rome had therefore not been transuranic elements, but radioactive isotopes of known elements from the middle of the periodic table. 

Actually, then, by our symbol jjU we are representing not an atom, but a nucleus. Our equation is written in terms of nuclei and particles associated with them. This nuclear equation tells us nothing about what compound ol uranium was bombarded with neutrons or what compound of barium is formed. We are summarizing only the nuclear changes. During the nuclear change there is much disruption of other atoms because of the tremendous amounts of energy liberated. We do not know in detail what happens but eventually we return to electrically neutral substances (chemical compounds) and the neutrons are consumed by other nuclei. 

As Z increases, the overall yield of the target element falls sharply, because many steps are required. Plutonium (element 94) has been produced in ton quantities by neutron bombardment of uranium-238. Up to curium (element 96), production in kilogram quantities is possible, but the yields fall by about one order of magnitude for each successive element beyond Z = 96. 

Beyond Z = 100, synthesis by neutron bombardment of uranium is no longer effective. Instead, nuclides in the Z = 95 to 99 range are bombarded with beams of light nuclei. For example, mendelevium (Z = 101) was first... 

The development of chemistry itself has progressed significantly by analytical findings over several centuries. Fundamental knowledge of general chemistry is based on analytical studies, the laws of simple and multiple proportions as well as the law of mass action. Most of the chemical elements have been discovered by the application of analytical chemistry, at first by means of chemical methods, but in the last 150 years mainly by physical methods. Especially spectacular were the spectroscopic discoveries of rubidium and caesium by Bunsen and Kirchhoff, indium by Reich and Richter, helium by Janssen, Lockyer, and Frankland, and rhenium by Noddack and Tacke. Also, nuclear fission became evident as Hahn and Strassmann carefully analyzed the products of neutron-bombarded uranium. 

Thorex [Thorium extraction] A process for separating the products from the nuclear breeder reaction in which uranium-233 is produced by the neutron bombardment of thorium-232. It uses solvent extraction into tri-n-butyl phosphate. Developed at the Oak Ridge National Laboratory, TN, in the early 1960s. See also Butex, Purex, Redox. 

Only a small fraction of Bk-249 is obtained by the above reaction because neutrons also induce fission. Alternatively, uranium—238 may be converted to Bk-249 by very short but intense neutron bombardment followed by five successive beta decays. 

Neptunium-239 may be obtained from uranium-238 by neutron bombardment as it was first produced ... 

Plutonium is produced from natural uranium which is a mixture of nonfis-sionable uranium-238 (99.3%) and fissionable uranium-235(0.7%). The first synthesis of this element was in a cyclotron generating plutonium in microgram quantities. The isotope Pu-239 can be produced in much larger quantities in a nuclear reactor, either a conventional thermal reactor or a breeder type reactor by neutron bombardment of uranium- 238. The nuclear reactions are shown below. 

Neutron bombardment converts thorium-232 to its isotope of mass 233. The thorium-233 formed undergoes two successive beta decays to form uranium-233, a fissionable material, similar to uranium-235 and plutonium-239. 

The element was discovered in the pitchblende ores by the German chemist M.S. Klaproth in 1789. He named this new element uranium after the planet Uranus which had just been discovered eight years earlier in 1781. The metal was isolated first in 1841 by Pehgot by reducing the anhydrous chloride with potassium. Its radioactivity was discovered by Henry Becquerel in 1896. Then in the 1930 s and 40 s there were several revolutionary discoveries of nuclear properties of uranium. In 1934, Enrico Fermi and co-workers observed the beta radioactivity of uranium, following neutron bombardment and in 1939, Lise Meitner, Otto Hahn, and Fritz Strassmann discovered fission of uranium nucleus when bombarded with thermal neutrons to produce radioactive iso-... 

Xenon occurs in the atmosphere at trace concentrations. It also occurs in gases from certain mineral springs. Xenon also is a fission product of uranium, plutonium, and thorium isotopes induced by neutron bombardment. The radioactive fission product, xenon-135, has a very high thermal neutron cross-section. The element has been detected in Mars atmosphere. 

The creation, by neutron bombardment of uranium, of the so-called transuraniums is based on the discovery of artificial radioactivity by M. and Mme. Joliot-Curie. Irene Curie was bom in Paris in September, 1897, the elder daughter of M. and Mme. Pierre Curie of honored memory. Both in Poland and in France she had many relatives who were devoting their lives to science, and from her earliest childhood she lived in a scientific atmosphere, among distinguished chemists and physicists. When Irene was less than a year old, her mother discovered the radioactive element polonium, which was destined to play an important part in the later researches of both mother and daughter. A few months later M. and Mme. Curie discovered another element of even greater importance, which they named radium. 

In 1934, Fermi (44) found that when uranium was bombarded with neutrons, it showed evidence of neutron capture and the production of... 

This element has not been found in any naturally occurring mineral but Seaborg believes it may exist in minute amounts as the result of neutron bombardment in uranium ores (63). Neptunium is not absorbed from the digestive tract of animals, but when it is injected it tends to accumulate in the bones. Subsequent loss from this site is very slow (64, 65). 

The three neutrons produced when uranium splits have the ability to split other U-235 nuclei and start a self-sustaining chain reaction. Whether a chain reaction takes place depends on the amount of fissionable material present. The more fissionable material that is present, the greater the probability that a neutron will interact with another U-235 nucleus. The reason for this involves the basic relationship between surface area and volume as mass increases. If a cube with a length of 1 unit is compared to a cube of 2 units, it is found that the surface area to volume ratio of the 1 unit cube is twice that of the 2 unit cube (Figure 17.6). This shows that volume increases at a greater rate than surface area as size increases. The probability that neutrons escape rather than react also depends on the surface area to volume ratio. The higher this ratio is the more likely neutrons escape. When a U-235 nucleus contained in a small mass of fissionable uranium is bombarded by a neutron, the... 

The rarity of polonium is evident from a calculation (1) which shows that the outermost mile of the earth s crust contains only 4000 tons of the element, whereas radium, usually classed as rare, is present to the extent of 1.8 X 107 tons. The abundance of polonium in uranium ores is only about 100 Mg per ton and hence separation of the element from such mineral sources cannot seriously be considered. However, radium, at equilibrium with its daughters, contains 0.02 wt % of polonium and, until recently, most of the element was obtained either from radium itself or, more usually, from expended radon ampoules which, after the radon decay is complete, contain radium-D and its daughters. Fortunately, however, the parent of polonium in these sources, bismuth-210, can be synthesized by neutron bombardment of natural bismuth [Bi209 (n,y) Bi210] and with the advent of the nuclear reactor it has become practicable to prepare milligram amounts of polonium. Almost all of the chemistry of the element recorded in the recent literature has been the result of studies carried out with polonium-210 prepared in this way. 

The lanthanide elements are very difficult to separate because of their highly similar chemistry, but the earlier actinide elements have sufficiently different redox chemistry to allow easy chemical separations. This is important in the nuclear power industry, where separations have to be made of the elements produced in fuel rods of nuclear power stations as fission products, and of the products Np and Pu, which arise from the neutron bombardment of the uranium fuel. 

P. Fabre, C. Magnor H. Muraour, Detonation of Nitrogen Iodide hv Fragments of the Uranium Nucleus Bombarded by Neutrons ,... 

After 1933 Fermi turned increasingly to experimental physics. Inspired by recent work in which artificial radioactive substances were produced by a-particle bombardment, Fermi and several collaborators used neutron bombardment to create several transuranic elements heavier than uranium, including plutonium. This work, and his finding that slow neutrons produce nuclear reactions more efficiently than fast ones, earned Fermi wide acclaim and the 1938 Nobel Prize in physics. After accepting the prize in Sweden, Fermi and his Jewish wife immigrated to the United States to escape the Nazis. 

In breeder reactors, the most common isotope of uranium, U-238, can be converted by neutron bombardment into fissionable Pu-239 (plutonium-239). The excess nuclear fuel can be used in other reactors or to build nuclear weapons. 

By using neutron and positive-ion bombardment, scientists have been able to extend the periodic table. Prior to 1940 the heaviest known element was uranium (Z = 92). However, in 1940 neptunium (Z = 93) was produced by neutron bombardment of The process initially gives 292U, which then decays to Np by /3-particle production ... 

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