Nuclear chemistry fission

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. 

This useful technique has made many contributions to radio- and nuclear chemistry, although primarily for investigational purposes rather than those of separation for its own ends. Thode and his co-workers have made many investigations into the inert gases produced in fission and it was by these means that the fine structure of fission was first discovered (79), (121). Since then several other elements, the rare-earths, strontium, caesium, zirconium, and molybdenum (35), (50), (132) have been investigated, and the isotopic ratios obtained provide relative values of fission-yields which are more accurate than can be obtained by standard radiochemical means. The latter technique, however, requires rather less heavily irradiated material than the former. 

J Ju elements in the periodic table exist in unstable versions called radioisotopes (see Chapter 3 for details). These radioisotopes decay into other (usually more stable) elements in a process called radioactive decay. Because the stability of these radioisotopes depends on the composition of their nuclei, radioactivity is considered a form of nuclear chemistry. Unsurprisingly, nuclear chemistry deals with nuclei and nuclear processes. Nuclear fusion, which fuels the sun, and nuclear fission, which fuels a nuclear bomb, are examples of nuclear chemistry because they deal with the joining or splitting of atomic nuclei. In this chapter, you find out about nuclear decay, rates of decay called half-lives, and the processes of fusion and fission. 

Figure 11.1 Schematic view of the fission process. (From J. E. Gindler and J. R. Huizenga, Nuclear Fission in Nuclear Chemistry, Vol. II, L. Yaffe, Ed. Copyright 1968 Academic Press, Reprinted by permission of Elsevier.)...

Volatilization processes, combined with gas adsorption chromatographic investigations, are well established methods in nuclear chemistry. Fast reactions and high transport and separation velocities are crucial advantages of these methods. In addition, the fast sample preparation for a-spectroscopy and spontaneous fission measurements directly after the gas-phase separation is a very advantageous feature. Formation probabilities of defined chemical compounds and their volatility can be investigated on the basis of experimentally determined and of predicted thermochemical data, the latter are discussed in Part II of this chapter. 

In recent years hea w-ater has been used in the field of nuclear chemistry. It is mentioned in the Smyth Report (see Chap. 33) that heavy water can be used instead of graphite as the moderator in a uranium pile. The function of the moderator is to reduce the speed of the fast neutrons emitted when nuclei undergo fission. The Canadian pile at Chalk River is a heavy-water pile. 

As you learned in the previous section, using nuclear fission reactions to generate electrical power is an important application of nuclear chemistry. Another very important application is in medicine, where the use of radioisotopes has made dramatic changes in the way some diseases are treated. This sechon explores the detection, uses, and effects of radiation. 

The discovery of nuclear fission has overshadowed all other recent developments in nuclear chemistry and physics. 

With the development of nuclear reactors and charged particle accelerators (commonly referred to as atom smashers ) over the second half of the twentieth century, the transmutation of one element into another has become commonplace. In fact some two dozen synthetic elements with atomic numbers higher than naturally occurring uranium have been produced by nuclear transmutation reactions. Thus, in principle, it is possible to achieve the alchemist s dream of transmuting lead into gold, but the cost of production via nuclear transmutation reactions would far exceed the value of the gold. SEE ALSO Alchemy Nuclear Chemistry Nuclear Fission Radioactivity Transactinides. 

The discovery of radioactivity a century ago opened up a new field in science, that of the atomic nucleus, which culminated 40 years later in the discovery of fission, and its practical consequences in the form of nuclear weapons and nuclear power reactors. That remains still die focus of news media as it influences international politics and national energy policies. However, nuclear science has contributed much more to our daily life as it has penetrated into practically every important area, sometimes in a pioneering way sometimes by providing conqiletely new solutions to old problems from the history of the universe and our civilisation to methods of food production and to our health from youth to old age. It is a fascinating field continuously developing. Nuclear chemistry is an important part of this. 

The developments in nuclear chemistry during the 1930s, the observation of nuclear fission in 1938, and the urgency of the Manhattan Project will launch this discipline into a decade of breakthroughs. Uranium 235, rather than its more abundant isotope U-238, is rapidly fissionable by neutrons. In 1941, Glenn Seaborg and coworkers discovered that tbeir newly discovered element, plutonium (specifically Pu-239), has fission properties comparable to U-235. The Berkeley 60-inch cyclotron, employed between the years 1939 and 1941, is displayed in the accompa-... 

Otto Hahn (Germany) for his discovery of the fission of heavy nuclei. Hahn s and his colleague s work discovered nuclear fission, and in particular that uremium could be split in a chain reaction by nuclear fission. This discovery was perhaps recognized as much for its importance as it was for its potential cbnger to society if not properly used and controlled, and Hahn himself was keenly aware of the potential for danger. Nonetheless, this discovery paved the way for much future research into nuclear chemistry, as well as for the development of modern nuclear reactors. 

The element, with atomic number 43 in the periodic table, was named technetium, a word derived from Greek meaning artificial. Thus, the name reflects the artificial origin of being produced by nuclear reactions, as no stable isotope of the element exists. Twenty-one radioactive isotopes of technetium and seven isomers are known from nuclear chemistry. Of these, only three isotopes have long physical half-lives Tc (T1/2 = 2.6 x 10 years), Tc (Ti/2 = 4.2x 10 years), and Tc (Ti/2 = 2.1 X 10 years). Being a long-lived fission product from neutron-induced fission of and... 

Take a look at the equation for the fission of U-235 in the preceding section. Notice that one neutron was used, but three were produced. These three neutrons, if they encounter other U-235 atoms, can initiate other fissions, producing even more neutrons. It s the old domino effect. In terms of nuclear chemistry, it s a continuing cascade of nuclear fissions called a chain reaction. The chain reaction of U-235 is shown in Figure 5-3. 

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