Fission induced

Am undergo fission with thermal neutrons of these isotopes and Pu are the most important as they are most readily obtainable. Other heavy nuclei require fast neutrons to induce fission such neutrons are much more difficult to control into a self-sustaining chain-reaction. 

In early 1941, 0.5 )-lg of Pu was produced (eqs. 3 and 4) and subjected to neutron bombardment (9) demonstrating that plutonium undergoes thermal neutron-induced fission with a cross section greater than that of U. In 1942, a self-sustaining chain reaction was induced by fissioning 235u... 

The nucleus """U (uranium) does not fission spontaneously, but It can be induced to fission through interaction with a neutron. Pictorially, a typical neutron-induced fission of " U producing two nuclei and three neutrons is depicted in Figure 2. 

The pictorial depiction of the neutron-induced fission of " U can be summarized as an equation ... 

Induced nuclear fission is fission caused by bombarding a heavy nucleus with neutrons (Fig. 17.23). The nucleus breaks into two fragments when struck by a projectile. Nuclei that can undergo induced fission are called fissionable. For most nuclei, fission takes place only if the impinging neutrons travel so rapidly that they can smash into the nucleus and drive it apart with the shock of impact uranium-238 undergoes fission in this way. Fissile nuclei, however, are nuclei that can be nudged into breaking apart even by slow neutrons. They include uranium-235, uranium-233, and plutonium-239—the fuels of nuclear power plants. 

If the three product neutrons strike three other fissile nuclei, then after the next round of fission there will be nine neutrons, which can induce fission in nine more nuclei. In the language of Section 13.9, neutrons are carriers in a branched chain reaction (Fig. 17.24). 

FIGURE 17.24 A self-sustaining chain reaction, in which neutrons are the chain carriers, takes place when induced fission produces more than one neutron per fission event. These newly produced neutrons can stimulate fission in increasingly greater numbers of other nuclei. 

Fission gives a range of product nuclides. Neutron-induced fission of U yields the distribution shown... 

C22-0017. Calculate the energy that is released per gram of U when induced fission gives... 

Fission chambers use neutron-induced fission to detect neutrons. The chamber is usually similar in construction to that of an ionization chamber, except that the coating material is highly enriched U235. The neutrons interact with the U235, causing fission. One of the two fission fragments enters the chamber, while the other fission fragment embeds itself in the chamber wall. 

The reaction of some cluster ions did induce fission of C-C bonds with 1-butene, but addition was the dominant reaction. 

The reactions of butadiene were very similar to the reactions of butane and 1-butene with addition being the most common reaction. The [V204]+ ion was the only ion to induce fission of butadiene but this was a minor pathway compared with the addition reaction. Only [V307]+ was involved in a dehydration reaction with butadiene to give the [V306C2H3]+ ion. 

Fission of the nucleus, whereby it splits into two roughly equal halves, is accompanied by a huge release of energy. It was first observed by Hahn and Strassman (1939), who were bombarding uranium with neutrons. Many heavy elements are susceptible to induced fission, but spontaneous fission can occur in some of the heaviest elements, and is thought to be the principal mode of decay for the transuranic elements. 

Nevertheless, the earth s crust contains technetium. Tc is formed by spontaneous fission of U as well as by slow neutron-induced fission of The first isolation of naturally occurring technetium was reported by Kenna and Kuroda , who isolated about 10" ng Tc from 5.3 kg of pitchblende. 

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 . 

Finally, when we are running out of cyclohexane, the process terminates by the interaction of two radical species, e.g. two chlorine atoms, two cyclohexyl radicals, or one of each species. The combination of two chlorine atoms is probably the least likely of the termination steps, since the Cl-Cl bond would be the weakest of those possible, and it was light-induced fission of this bond that started off the radical reaction. Of course, once we have formed cyclohexyl chloride, there is no reason why this should not itself get drawn into the radical propagation steps, resulting in various dichlorocyclohexane products, or indeed polychlorinated compounds. Chlorination of an alkane will give many different products, even when the amount of chlorine used is limited to molar ratios, and in the laboratory it is not going to be a particularly useful process. 

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. 

Actinides, the chemical elements with atomic numbers ranging from 89 to 103, form the heaviest complete series in the Periodic Table. They are radioelements, either naturally occurring or synthesized by nuclear reactions. Their predominant practical application depends on the nuclear properties of their isotopes decay, spontaneous or induced fission. Their chemical and physical properties reflect a very complex electronic structure, and their study and understanding are a challenge to experimentalists and theoreticians. 

By this time, Rutherford had evidence that hydrogen nuclei could come from more complex nuclei (56). In 1919, he reported an anomalous effect when he subjected diy air to a particles H atoms seemed to be produced even when there was no hydrogen in the system Rutherford correctly interpreted the presence of H nuclei as a sign that the a particles caused some sort of transmutation, and that the H nuclei were fragments of that reaction. I infer from Rutherford s use of the term disintegration that he pictured the reaction as an induced fission of nitrogen. In fact, the reaction was + He — + H. Rutherford and his associates... 

Figure 11.8 Neutron total and subbarrier fission cross sections of 240Pu as a function of neutron energy between 0.5 and 3 keV. (From H. Weigmann, Neutron-Induced Fission Cross Sections in C. Wagemans, The Nuclear Fission Process. Copyright 1991 CRC Press. Reprinted by permission of CRC Press.)...

Figure 11.13 Smoothed fragment mass distributions for the thermal neutron-induced fission of 233U, 235U, and 239Pu. [From Seaborg and Loveland (1990).]...

Figure 11.18 Yields of products from the thermal neutron-induced fission of 235U. (From A. C. Wahl. Nuclear Charge Distribution in Fission, in New Directions in Physics, N. Metropolis, D. M. Kerr, and G. C. Rota, Eds. Copyright 1987 by Academic Press, Inc. Reprinted by permission of Elsevier.)...

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