Fission induced nuclear

Some heavy nuclei will fission spontaneously. Others can be induced to fission through interaction with a neutron. In both spontaneous nuclear fission and induced nuclear fission the pool of neutrons and protons is conseiwed. For example, the nucleus "" Cf (Californium) fissions spontaneously. The 98 protons and 154 neutrons in the nucleus of Cf are reconfigured into other nuclei. Usually a few neu-... 

Any combination of reaction products consistent with these conseiwation principles is possible. For example, in the neutron-induced nuclear fission of it is possible to produce Xe, Sr, two neutrons, and 185 MeV of energy. The most likely reaction products are close in atomic number to xenon pCe) and strontium (Sr), but the possibilities number in the hundreds. 

Describing a neutron-induced nuclear fission reaction such as... 

The fission ofor Tu liberates, on average, two to three neutrons. One neutron is required to sustain the nuclear fission chain reaction. In a nuclear breeder reactor, the extra neutrons are used to induce nuclear reactions that lead to the production of Tu. The sequence begins by arranging for... 

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. 

FIGURE 17.23 In induced nuclear fission, the impact of an incoming neutron causes the nucleus to break apart. 

Structural materials for fission reactors (as well as for future fusion reactors) are being exposed to intense neutron flux for many years. In the case of fusion reactor, 14-MeV neutrons, produced by the fusion reaction of d + t He + n, induce nuclear reactions of... 

Additional interactions of neutrons with nuclei include die release of charged particles by neutron-induced nuclear disintegration, Commonly known reactions are n-p. n — d. and n—ct. In these cases, the incident neutrons may contribute part of their kinetic energy to the target nucleus to effect the disintegration. Hence, more than mere neutron capture is involved, Then, there is usually a lower threshold for the neutron energy below which the reaction fails to occur, Another important reaction involving neutrons is fission, which may occur under different conditions for eidier slow or fast neutrons with appropriate fissionable material. 

Nuclear fission reactors ( nuclear power reactors ) are devices that use controlled neutron-induced fission to generate energy. While a complete description of the design of these devices is beyond the scope of this book, there are certain basic principles related to nuclear reactors that are worth studying and that can be described and understood with a moderate effort. 

Radioactive xenon (radioxenon) is produced by the fissioning of nuclear material, either via neutron-induced or spontaneous fission, and also via neutron activation or other nuclear reactions involving xenon gas. The most abundant radioactive xenon isotopes in... 

Induced nuclear fission reactions depend on chain reactions the fission reaction is maintained by the two or three neutrons set free in each fission. 

Nuclear fission is the breaking apart of atomic nuclei into two or more pieces. This can take place spontaneously in the case of the heaviest atoms. Neutron bombardment of atoms can also cause the nuclei to break apart. This process is called induced nuclear fission. Atoms that undergo this process are called fissionable. Some nuclides can undergo fission with slow (not very energetic, or thermal) neutrons. These atoms are called fissile. 

A nuclear reactor is a device in which the fission process is controlled, either to produce power, radionuclides, or both. All nuclear reactors depend upon an initial load of fuel that contains fissile materials. Absorption of a neutron by a fissile nucleus produces another fission event with high probability, accompanied by the emission of more neutrons. If one of the neutrons emitted in each fission induces another fission, the number of neutrons in each succeeding generation will remain constant and the neutron economy is balanced. This is referred to as a self-sustaining chain reaction, and is the normal operating condition of a nuclear reactor. (See O Chaps. 57 and O 58 in this Volume.)... 

Neutron-induced nuclear fission can be described by the general equation (according to Lieser, 1991)... 

Another secondary effect is the production of radionuclides which themselves are not fission products but which are generated by neutron capture in long-lived or stable fission product nuclides. Examples of the products of such reactions are Cs and Cs, which are separated from the true members of the isobaric chains by the stable nuclides Xe and Xe, and which are formed by neutron capture in the fission products Cs and Cs, respectively. Because of the two-fold neutron-induced nuclear reaction which is necessary for their production, their concentration in the irradiated fuel depends approximately on the square of the local neutron fluence. 

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