Uranium fissioning

Many of the uranium fission fragments are radioactive. Of special interest are technetium-99 [14133-76-7] and iodine-129 [15046-84-1] having half-Hves of 2.13 X 10 yr and 1.7 x 10 yr, respectively. Data on all isotopes are found in Reference 6 (see also Radioisotopes). 

Bi-functional radio-analytical scheme, based on exchange and extraction column chromatography, which provides the reliable information on molybdenum and uranium contents in biological materials has been elaborated. The contribution of uranium fission reaction has been strictly monitored. The uncertainty of the results of Mo determination by the presented method is very low. 

The last missing element Z = 61 (Pm) discovered among uranium fission products... 

Uranium is used as the primai-y source of nuclear energy in a nuclear reactor, although one-third to one-half of the power will be produced from plutonium before the power plant is refueled. Plutonium is created during the uranium fission cycle, and after being created will also fission, contributing heat to make steam in the nuclear power plant. These two nuclear fuels are discussed separately in order to explore their similarities and differences. Mixed oxide fuel, a combination of uranium and recovered plutonium, also has limited application in nuclear fuel, and will be briefly discussed. 

Jacob A. Marinsky ( 1918) as well as L. E. Glendenin and Charles D. Coryll ( 1912) detected the element at Oak Ridge. The first conclusive proof was in uranium piles. Uranium fission gives rise to fragments with nuclei of atomic number 61. 

Element 43 from Uranium Fission. U. S. Atomic Energy Commiss. Doc., AECD. 2043 (June 1948). 

Separation of Technetium from Uranium Fission Products.114... 

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 . 

Table 4. Distribution coefllcients of uranium fission products in pyridine. Extraction from 0.25 M NaOH + 2.0 M Na COj ...

For the extraction of Tc from molybdemun irradiated by neutrons or separated from uranium fission products, inorganic sorbents, especially aliuninum oxide have widely been applied. In preparing a Tc generator from irradiated molybdenum , MoOj is dissolved in cone, nitric acid, the solution is diluted and passed through an aluminum oxide column. The column is then eluted by 0.2 N H2SO4 to extract Tc. If molybdenum is adsorbed by AljOj as molybdatophos-phate instead of molybdate, the exchange capacity of molybdenum increases from... 

For the rapid determination of Tc in a mixture of uranium fission products. Love and Greendale have used the method of amalgam polarography. It consists in a selective reduction of technetium at a dropping mercury electrode at a potential of —1.55 V vs. SCE in a medium of 1 M sodium citrate and 0.1 M NaOH. Under these conditions, technetium is reduced to an oxidation state which is soluble in mercury. The amalgam is removed from the solution of fission fragments and the amount of Tc determined in nitric acid solution of the amalgam by a y count. For Tc the measurement accuracy is within 1 %, and the decontamination factor from other fission products 10 . 

The major characteristic of technetium is that it is the only element within the 29 transition metal-to-nonmetal elements that is artificially produced as a uranium-fission product in nuclear power plants. It is also the tightest (in atomic weight) of all elements with no stable isotopes. Since all of technetiums isotopes emit harmful radiation, they are stored for some time before being processed by solvent extraction and ion-exchange techniques. The two long-lived radioactive isotopes, Tc-98 and Tc-99, are relatively safe to handle in a well-equipped laboratory. 

Promethium is a silvery-white, radioactive metal that is recovered as a by-product of uranium fission. Promethium-147 is the only isotope generally available for smdy. The spectral lines of promethium can be observed in the light from a distant star in the constellation Andromeda. Even so, it is not found naturally on Earth, and scientists consider it to be an artificial element. Its melting point is 1,042°C, its boiling point is estimated at 3,000°C, and its density is 7.3 g/cm. ... 

Promethium does not occur in metallic form in nature. Minute quantities are associated with other rare earths. It also is detected in uranium fission products. It is probably the rarest of the lanthanide elements. 

The discovery of uranium fission by Enrico Fermi and L. Szilard at Columbia University opened the way for further advances. This work was done under the cloak of wartime secrecy and led directly to the atomic bomb, but its significance for the discovery of new elements was very great. 

Subsequently is was prepared by bombardment of molybdenum by neutrons, and of niobium with helium ions, as well as by uranium fission (5). 

Here is the equation for a typical uranium fission reaction ... 

C.A. Arrhenius, in 1787, noted an unusual black mineral in a quarry near Ytterby. Sweden, This was identified later as containing yttrium and rare-earth oxides. With the exception of promethium, all members of the Lanthanide Series had been discovered by 1907, when lutetium was isolated. In 1947. scientists at the Atomic Energy Commission at Oak Ridge National Laboratory (Tennessee) produced atomic number 61 from uranium fission products and named it promethium. No stable isotopes of promethium have been found in the earth s crust. 

At the same time, the study of uranium fission guided Ya.B. toward problems of microphysics, the theory of elementary particles and the nucleus. Thus, the work of 1939-1941 became a decisive turning point in Ya.B. s life and career. 

Forming a natural group with Ya.B. s papers on uranium fission and elementary particles are a small, but fundamentally important group of papers on nuclear physics which have had major repercussions. 

Solvent extraction was first applied to metal separation in the nuclear industry in the late 1940s. Nuclear power generation by uranium fission produces spent fuel containing 238U, 235U, 239Pu, 232Th, and many other radioactive elements collectively known as fission products. 

The nuclear fuels were created in the cosmic event that created the universe and were deposited in the earth as it took form. There are two families of nuclear fuels, those for fission (uranium and thorium) and those for fusion (protium [[//], deuterium, helium-3, and lithium). Only uranium fission has been developed as a commercial source of nuclear energy. Although fusion has been developed as a military weapon, the hydrogen bomb, it is premature to include the fusion fuels in the world s inventory of capital energy. The technology for controlled fusion is not available, nor is development of a controlled fusion process expected in the next several decades. When available it would increase the capital supply to a level greater than that from all other sources combined.16... 

The possibility of a chain reaction obsessed nuclear physicists. Why had not the chain reaction of uranium fission actually occurred Niels Bohr and a former student, John A. Wheeler of Princeton University, puzzled over this question. 

At a meeting of the American Physical Society at Columbia University on February 17, 1939, they advanced a theory of uranium fission which postulated that not all the uranium employed as target actually fissioned. They believed that less than one percent of their uranium target disintegrated because only one of the three isotopes of uranium was actually capable of fission. This fissionable isotope first discovered in 1935 by Arthur Dempster of the University of Chicago, has an atomic weight of 235 instead of 238 which is the atomic weight of 99.3% of the uranium mixture found in nature. U-238 is extremely stable its half-life has been estimated to be four billion years. 

A direct synthesis of N2F2 in low yield and admixed with other nitrogen fluorides has been reported from the irradiation of N2-F2 mixtures with ra-y-radiation from a nuclear reactor admixed with other high-energy radiation from uranium fission products (85). There is also a radiochemical synthesis of N2F2 (1.5%) and NF3 (42%) when an N2-F2 mixture is irradiated with 30-MeV electrons in an electron linear accelerator (86). Reaction of fluorine diluted with N2 and NH3 also gives some N2F2 (159,213). 

The existence of the element was recognized by Klaproth in 1789, but only in 1841 did Peligot actually isolate the metal itself. However, it was not until the discovery of uranium fission by Meitner, Hahn, and Strassmann in 1939 that it became commercially important. Its most important ores are uraninite (usually called pitchblend, and approximating to U02) and uranium vanadates. 

The development of cyclotrons and nuclear reactors in the middle of the 20th century made possible the production of radioactive isotopes which are not naturally present in any significant quantity on Earth. Thus in a nuclear reactor some of the neutrons released by uranium fission may be absorbed by leading to the formation of Pu. 

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