0-fission reaction

In nuclear chemistry, a fission reaction (see atomic energy) may be initiated by a neutron and may also result in the production of one or more neutrons, which if they reacted in like manner could start a chain reaction. Normally, moderators such as cadmium rods which absorb neutrons are placed In the reactor to control the rate of fission. 

In the above examples the size of the chain can be measured by considering the number of automobile collisions that result from the first accident, or the number of fission reactions which follow from the first neutron capture. When we think about the number of monomers that react as a result of a single initiation step, we are led directly to the degree of polymerization of the resulting molecule. In this way the chain mechanism and the properties of the polymer chains are directly related. 

Del y for Dec y. Nuclear power plants generate radioactive xenon and krypton as products of the fission reactions. Although these products ate trapped inside the fuel elements, portions can leak out into the coolant (through fuel cladding defects) and can be released to the atmosphere with other gases through an air ejector at the main condenser. 

Unstable niobium isotopes that are produced in nuclear reactors or similar fission reactions have typical radiation hazards (see Radioisotopes). The metastable Nb, = 14 yr, decays by 0.03 MeV gamma emission to stable Nb Nb, = 35 d, a fission product of decays to stable Mo by... 

Control of the core is affected by movable control rods which contain neutron absorbers soluble neutron absorbers ia the coolant, called chemical shim fixed burnable neutron absorbers and the intrinsic feature of negative reactivity coefficients. Gross changes ia fission reaction rates, as well as start-up and shutdown of the fission reactions, are effected by the control rods. In a typical PWR, ca 90 control rods are used. These, iaserted from the top of the core, contain strong neutron absorbers such as boron, cadmium, or hafnium, and are made up of a cadmium—iadium—silver alloy, clad ia stainless steel. The movement of the control rods is governed remotely by an operator ia the control room. Safety circuitry automatically iaserts the rods ia the event of an abnormal power or reactivity transient. 

The technologically most important isotope, Pu, has been produced in large quantities since 1944 from natural or partially enriched uranium in production reactors. This isotope is characterized by a high fission reaction cross section and is useful for fission weapons, as trigger for thermonuclear weapons, and as fuel for breeder reactors. A large future source of plutonium may be from fast-neutron breeder reactors. 

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. 

Phenomene d Oklo, Proceedings of a Symposium on the Oklo Phenomenon, International Atomic Energy Agency, Vienna, Proceedings Series, 1975. Natural Fission Reactions, IAEA, Vienna, Panel Proceedings Series STI/PUB/475, 1978, 754 pp. R. West, Natural nuclear reactors. J. Chem. Ed. 53, 336-40 (1976). 

A nuclear fission reaction will not occur unless the following occur (1) the total mass of the reaction products is less than the total mass of the interacting nuclei, and (2) the sum of the neutrons and the sum of the protons in the interacting particles ecjuals the sum of the neutrons and the sum of the protons in the products of the fission. 

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

The products of nuclear fission reactions are radioactive and disintegrate according to their own time scales. Often disintegration leads to other radioactive products. A few of these secondary products emit neutrons that add to the pool of neutrons produced by nuclear fission. Very importantly, neutrons from nuclear fission occur before those from radioactive decay. The neutrons from nuclear fission are termed prompt. Those from radioacth e decay arc termed delayed. A nuclear bomb must function on only prompt neutrons and in so doing requires nearly 100 percent pure (or Pu) fuel. Although reactor... 

Reality Check Comparing the answers to (a) and (b), it appears that the fusion reaction produces about seven times as much energy per gram of reactant (57.2 X 107 versus 8.19 X 107 kj) as does the fission reaction. This factor varies from about 3 to 10, depending on the particular reactions chosen to represent the fusion and fission processes. 

Consider file fission reaction in which U-235 is bombarded by neutrons. The products of the bombardment are rubidium-89, cerium-144, beta particles, and more neutrons. 

Perhaps you have already recognized our nuclear reaction as a fission reaction. It is of (he type of reaction used in an atomic pile, the energy source of a nuclear... 

If we wish to gain some idea of the alteration of mass in a nuclear change, we cannot use the fission reaction because the exact masses of the nuclei involved are not known. Let us look at another type of reaction of possible importance in the production of nuclear energy ... 

The two nuclei on the right side are just two of the many possible products of the fission process. Since more than one neutron is released in each process, the fission reaction is a self-propagating, or chain reaction. Neutrons released by one fission event may induce other fissions. When fission reactions are run under controlled conditions in a nuclear reactor, the energy released by... 

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