Nuclear chemistry radioactivity

Multimedia Nuclear Chemistry—radioactive half-life. 

In 1921, Irene Curie (1897-1956) began research at the Radium Institute. Five years later she married Frederic Joliot (1900-1958). a brilliant young physicist who was also an assistant at the Institute. In 1931, they began a research program in nuclear chemistry that led to several important discoveries and at least one near miss. The Joliot-Curies were the first to demonstrate induced radioactivity. They also discovered the positron, a particle that scientists had been seeking for many years. They narrowly missed finding another, more fundamental particle, the neutron. That honor went to James Chadwick in England. In 1935,... 

Some isotopes that occur in nature are unstable and are said to be radioactive. A few radioactive isotopes, such as uranium-238 and carbon-14, are found on Earth, and many others can be synthesized in nuclear chemistry laboratories, as we describe in Chapter 22. Over time, radioactive isotopes decompose into other stable isotopes. Unstable isotopes decompose in several ways. Most nuclei that have Z > 83 decompose by giving off a helium... 

Nuclear chemistry nuclear equations, half-lives, and radioactivity chemical applications... 

Radioactive decay is a first-order process, and the half-lives of the radioisotopes are well documented (see the chapter on Nuclear Chemistry for a discussion of half-lives with respect to nuclear reactions). 

Despite their instability, some unstable atoms may last a long time the half-life of uranium 238, for example, is about 4.5 billion years. Other unstable atoms decay in a few seconds. Radioactive decay is one of the topics of nuclear chemistry, and it involves nuclear forces, as governed by advanced concepts in chemistry and physics, such as quantum mechanics. Researchers do not fully understand why some atoms are stable and others are not, but most radioactive nuclei have an unusually large (or small) number of neutrons, which makes the nucleus unstable. And all heavy nuclei found so far are radioactive—nuclides with an atomic number of 83 or greater decay. 

How would you know if you have made a new element Neutron irradiation of a small sample of uranium could be expected to produce only an extremely tiny amount of element 93, perhaps a thousand atoms or so. Because they are radioactive, such atoms should be easy to spot with a Geiger counter. But first you need to separate them from the uranium, which is radioactive too. This is why the nuclear physicists needed the help of chemists. From its beginning with the work of the Curies, nuclear chemistry or radiochemistry has had to work with incredibly tiny samples of rare elements, and has required a skill at analysis - separating substances into their elemental components - that Antoine Lavoisier could never have dreamed of. 

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. 

Chart of the nuclides organizing elements by their nuclear properties Radioactive elements and their modes of decay The periodic table organizing elements by their chemistry properties Chemical bonding... 

The Sr-82 used in these studies was produced by spallation of a molybdenum target with 800 MeV protons at the Los Alamos Meson Physics Facility (LAMPF) and radiochemically separated by the Nuclear Chemistry Group at Los Alamos Scientific Laboratory (LASL) (22). The major radionuclidic contaminant in the Sr-82 is Sr-85 which is present in at least 1 1 ratio relative to Sr-82. The actual ratio depends upon the length of time after the production of radioactive strontium. Because of the 65 day half life of Sr-85 and the 25 day half life of Sr-82, the Sr-85 Sr-82 ratio increases with time. Other radionuclides found by the Hammersmith group in the processed Sr-82/85 shipment were Sr-89 ( 1%), Sr-90 ( 0.01%), Co-58 ( 1%) and Rb-84 ( 1%) from (17). 

Inevitably developments in all fields of analytical chemistry find their applications to the problems of the chemist in the field of petroleum. Thus ion exchange, microwave techniques, nuclear resonance, radioactive isotopes, activation analysis, high frequency vibrations, and other developments of fundamental research should find applications in the field of petroleum analysis. 

All the chemical changes and many of the physical changes that we have studied so far involve alterations in the electronic structures of atoms. Electron-transfer reactions, emission and absorption spectra, and X rays result from the movement of electrons from one energy level to another. In all of these, the nuclei of the atoms remain unchanged, and different isotopes of the same element have the same chemical activity. Nuclear chemistry, or radioactivity, differs from other branches of chemistry in that the important changes occur in the nucleus. These nuclear changes also are represented by chemical equations. However, because the isotopes of the same element may, from a nuclear standpoint, be very different in reactivity, it is necessary that the equations show which isotopes are involved. 

Nuclear chemistry consists of a four-pronged endeavor made up of (a) studies of the chemical and physical properties of the heaviest elements where detection of radioactive decay is an essential part of the work, (b) studies of nuclear properties such as structure, reactions, and radioactive decay by people trained as chemists, (c) studies of macroscopic phenomena (such as geochronology or astrophysics) where nuclear processes are intimately involved, and (d) the application of measurement techniques based upon nuclear phenomena (such as nuclear medicine, activation analysis or radiotracers) to study scientific problems in a variety of fields. The principal activity or mainstream of nuclear chemistry involves those activities listed under part (b). 

One term that is frequently associated with nuclear chemistry is that of radiochemistry. The term radiochemistry refers to the chemical manipulation of radioactivity and associated phenomena. All radiochemists are, by definition, nuclear chemists, but not all nuclear chemists are radiochemists. Many nuclear chemists use purely nonchemical, that is, physical techniques, to study nuclear phenomena, and thus their work is not radiochemistry. 

Why do some nuclei undergo radioactive decay while others do not Why, for instance, does a carbon-24 nucleus, with six protons and eight neutrons, spontaneously emit a /3 particle, whereas a carbon-23 nucleus, with six protons and seven neutrons, is stable indefinitely Before answering these questions, it s important to define what we mean by "stable." In the context of nuclear chemistry, we ll use the word stable to refer to isotopes whose half-lives can be measured, even if that half-life is only a fraction of a second. We ll call those isotopes that decay too rapidly for their half-lives to be measured unstable, and those isotopes that do not undergo radioactive decay nonradioactive, or stable indefinitely. 

The field of nuclear medicine actively uses several different techniques involving radioactive materials and high-energy electromagnetic radiation to effectively diagnose and treat disease. Our treatment of nuclear medicine presented here is very brief and far from comprehensive. The interested student should refer to a modern nuclear chemistry or nuclear medicine textbook for more details of the various techniques discussed in this section. 

Late in 1938, in Berlin-Dahlem, an experimenter in nuclear chemistry touched off a wave of excitement throughout the world which even reached the front pages of the most conservative newspapers. At the Kaiser Wilhelm Institute for Chemistry, only a few miles from Hitler s Chancellery, three researchers had proceeded to repeat some experiments first performed by Enrico Fermi in Rome in 1934. The Italian scientist, in an attempt to produce the Curies artificial radioactivity in the very heavy elements by bombarding them with neutrons, believed he had created an element (No. 93) even heavier than uranium. 

Nuclear chemistry describes reactions involving changes in atomic nuclei. In Lesson 2, elements were defined as matter that cannot be broken down by simple means. Some isotopes are radioactive and are broken down by nuclear processes. Radioactivity is the process by which unstable nuclei break down spontaneously, emitting particles and/or electromagnetic radiation (i.e., energy), also called nuclear radiation. Heavy elements (from atomic number 83) are naturally radioactive, and many more (the transuranium elements, atomic numbers 93 to 116) have been generated in laboratories. 

K. Bachmann, Messung radioaktiver Nuklide (Ed. K. II. Lieser), Verlag Chemie, Weinheim, 1970 J. H. Hamilton (Ed.), Radioactivity in Nuclear Spectroscopy, Modern Techniques and Applications, Vols. I and II, Gordon and Breach, New York, 1972 J. Krugers (Ed.), Instrumentation in Applied Nuclear Chemistry. Plenum Press, New York. 1973 J. Ceniy (Ed.), Nuclear Spectro.scopy and Reactions, Vols. A, B and C, Academic Press, New York, 1974... 

O. Hahn, Applied Radiochemistrry, Cornell University Press, Ithaca, NY, 1936 A. C. Wahl, N, A. Bonner, Radioactivity Applied to Chemistry, Wiley, New York, 1951 M. Haissinsky, Nuclear Chemistry and its Applications, Addison-Wesley, Reading, MA, 1964 E. A. Evans, M. Muramatsu (Eds.), Radiotracer Techniques and Applications, Marcel Dekker, New York, 1977... 

Hot-atom chemistry Chemical effects of nuclear transfonnations (radioactive decay or nuclear reactions)... 

Nuclear Chemistry the chemistry of radioactive elements and of reactions involving the nuclei of atoms. 

Nuclear chemistry (radiochemistry) has now become a large and very important branch of science. Over four hundred radioactive isotopes have been made in the laboratory, whereas only about three hundred stable isotopes have been detected in nature. Three elements —technetium (43), astatine (85), and promethium (61), as well as some trans-uranium elements, seem not to occur in nature, and are available only as products of artificial transmutation. The use of radioactive isotopes as tracers has become a valuable technique in scientific and medical research. The controlled release of nuclear energy promises to lead us into a new world, in which the achievement of man is no longer limited by the supply of energy available to him. 

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