Primary fission products

An earlier study by Baumgartner and Reichold (11) shows further that even single metal atoms can react with available CO molecules to produce carbonyls. By irradiating a mixture of powdered Cr(CO)j and UjOg, they were able to catch the fission product Mo and isolate it as Mo(CO)g. This clearly indicates that molecule formation is not dependent on previously formed bonds. The yields of Mo(CO)6 (60%) were too high to represent only the primary fission product molybdenum atoms, and indicate that some short-lived precursors of Mo ( Zr, Nb) may also have formed at least tentative metal-CO bonds, and produced Mo(CO)g after )3-decay. 

Primary fission products, secondary Sl deexcited fission fragments in their V ground state. These nuclei are far removed from beta stability and are radioactive. 

In discussions of fission, one frequently hears the terms cumulative yield and independent yield. The independent yield of a nuclide is just what it appears, the yield of that nucleus as a primary fission product. Because the fission products are all (3 emitters, they decay toward the bottom of the valley of (3 stability, populating several different members of an isobaric series, as, for example, with A = 140 fragments ... 

The same cleavage reaction occurs in rotenoids containing the chromanochromanone system (105).63,57 From the primary fission product of the retro-Diels-Alder decomposition [107], containing rings A and B, a highly stabilized aromatic system is formed by loss of a hydrogen atom, (105)->[107]->[108]. 

Fission of heavy nuclei always results in a high neutron excess of the hssion products, because the neutron-to-proton ratio in heavy nuclides is much larger than in stable nuclides of about half the atomic number, as already explained for spontaneous hssion (Fig. 5.15). The primary fission products formed in about 10 " s by fission and emission of prompt neutrons and y rays decay by a series of successive / transmutations into isobars of increasing atomic number Z. The final products of these decay chains are stable nuclides. 

The oxidative cleavage of unsaturated ketones takes place under the same conditions as that of alkenes or other unsaturated derivatives. The fate of the primary fission product depends on the position of the double bond with respect to the carbonyl group and on the subsequent reactions. Ozonization of A -cholestenone in acetic acid and ethyl acetate, followed by treatment with 30% hydrogen peroxide, gives a keto acid, evidently resulting from the decomposition of the primarily formed diketo acid (equation 444) [1176]. 

The yield of primary fission products in relation to their mass number is shown in Fig. 8. Most of the radioactive fission products have short half-lives, but some decay slowly technetium-99 has 2.2 x 10 yr and promethium-147, 2.6 yr. Two of the most useful fission products obtained in the operation of a pile are caesium-137 (/ -, 33 yr) and strontium-90 ( +, 22 yr). The former is used in medicine and the latter in medicine and industry both are separated from shorter-lived material. 

More than 300 different nuclides have been observed as the primary products of fission. The term fission products usually refers to the primary fission products, i.e., the fission fragments and their daughters resulting from radioactive decay and neutron absorption. Only a few of the primary fission products are stable, the rest being beta-emitting radionuclides. As a fission-product radionuclide undergoes beta decay, its atomic number increases whereas its mass number remains constant. The direct yield of a fission-product nuclide is the fraction of the total fissions that yield this nuclide, essentially as a direct-fission fragment. The cumulative... 

To convert olefins into carboxylic acids in this way it is preferable to oxidize the primary fission products of the ozonide in a subsidiary reaction. Particularly good results were obtained by Asinger using a hot suspension of silver oxide116 and by Wilms using peracetic acid 117 Wilms thus obtained adipic acid in yields of about 90% from cyclohexene ... 

The primary fission products A and B are formed with a proton-to-neutron ratio which is less than that for stable nuclei of the same mass. The fragments are therefore proton deficient and undergo a series of j3 -decays in a chain until they attain stability. Each mode of fission, therefore, leads to two such chains. For example, mass chains 133 and 101 may be complementary masses in the above fission process where v the average number of neutrons emitted per fission is 2. In this case, the mass chains are as follows... 

As an example, is not formed to any appreciable extent in fission because it is shielded by the stable Xe. Hence, no Cs is normally observed in the remains after a nuclear explosion in the atmosphere. However, primary fission products in the A 133 isobar chain have time to decay to stable Cs during reactor operation and Cs is produced by the reaction Cs (n,y) Cs. Giv the cooling time, the ratio between the decay rates of Cs and Cs can be used to estimate the bumup of fuel from a given reactor, see Figure 21.6. 

Fission. The splitting of an atomic nucleus into two fragments that usually releases neutrons and y rays. Eission may occur spontaneously or may be induced by capture of bombarding particles. Primary fission products usually decay by particle emission to radioactive daughter products. The chain reaction that may result in controlled burning of nuclear fuel or in an uncontrolled nuclear weapons explosion results from the release of 2 or 3 neutrons/fission. Neutrons cause additional fissile nuclei in the vicinity to fission, producing still more neutrons, in turn producing still... 

So far, essentially mass-yield curves were dealt with. Each point of such a curve represents the formation cross section of isobaric nuclei of mass number A, composed of different combinations of protons and neutrons. Because heavy, fissile nuclei are generally more neutron rich than stable nuclides with about half their mass, fission products are generally also more neutron rich than stable nuclides of the same mass, even after the loss of a few prompt neutrons. (Example The symmetric fission of the compound nucleus (Z - 92, N -144) would form two/raiment nuclei of Pd (Z = 46, iV= 72). Assuming the emission of one prompt neutron, the corresponding primary fission product would be Pd. The stable isobar in mass chain with A = 117 is, however, Sn (Z -50, N- 67). As a consequence, the nucleus Pd would have to undergo a sequence of four P decays to reach stability.) Thus, the products... 

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