Nuclear chemistry radioactive decay

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

Nuclear chemistry is the study of changes in atomic nuclei. Such changes are termed nuclear reactions. Radioactive decay and nuclear transmutation are nuclear reactions. 

The conceptual problems start when considering materials such as plutonium, which is a by-product of the nuclear electricity industry. Plutonium is one of the most chemically toxic materials known to humanity, and it is also radioactive. The half-life of 238Pu is so long at 4.5 x 108 years (see Table 8.2) that we say with some certainty that effectively none of it will disappear from the environment by radioactive decay and if none of it decays, then it cannot have emitted ionizing a and f) particles, etc. and, therefore, cannot really be said to be a radioactive hazard. Unfortunately, the long half-life also means that the 238Pu remains more-or-less for ever to pollute the environment with its lethal chemistry. 

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). 

Both unimolecular and bimolecular reactions are common throughout chemistry and biochemistry. Binding of a hormone to a reactor is a bimolecular process as is a substrate binding to an enzyme. Radioactive decay is often used as an example of a unimolecular reaction. However, this is a nuclear reaction rather than a chemical reaction. Examples of chemical unimolecular reactions would include isomerizations, decompositions, and dis-associations. See also Chemical Kinetics Elementary Reaction Unimolecular Bimolecular Transition-State Theory Elementary Reaction... 

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. 

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... 

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). 

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. 

Rutherford s work has made him known as the father of nuclear physics with his research on radioactivity (alpha and beta particles and protons, which he named), and he was the first to describe the concepts of half-life and decay constant. He showed that elements such as uranium transmute (become different elements) through radioactive decay, and he was the first to observe nuclear reactions (split the atom in 1917). In 1908 he received the Nobel Prize in chemistry for his investigations into the disintegration of the elements, and the chemistry of radioactive substances. He was president of the Royal Society (1926-30) and of the Institute of Physics (1931-33) and was decorated with the Order of Merit (1925). He became Lord Rutherford in 1931. 

The fact that atoms were not eternally stable became evident in the discovery of radioactivity by Becquerel, followed by the extensive investigations of nuclear transformations by Marie Curie, Rutherford, Soddy, and others. Atoms thus are not indivisible eternal building blocks, but rather entities having a life history from their birth from simpler atomic nuclei by nuclear fusion to their decay or fusion to form other atoms. Radioactive decay is the conversion in time of some atoms into others and thus makes clear the inadequacy of using the atoms now known as starting points for the construction of chemistry. 

In the case of Tc pharmaceuticals, chemistry and safety have been compounded into kits, which have overcome the limitations set by radioactive decay and the risk of bacterial contamination. Kits are manufactured in advance in accordance with GMP requirements for the manufacture of sterile medicinal products, have a long shelf life, and facilitate ad hoc labeling whenever there is a demand in nuclear medicine. Kits provide safety and ease of preparation of highly complex molecules by using aseptic techniques for labeling. Consequently, quality control requirements for kit preparations rely merely on testing the radiochemical purity of a " Tc pharmaceutical to demonstrate stability in compliance with the purity requirements stated in the pharmacopeia. 

Tc pharmaceuticals mark the begiiming of diagnostic nuclear medicine and have contributed to patient care worldwide. Since the short-lived radionuclide was introduced for thyroid imaging in 1964, it has attracted much attention and stimulated clinical research. Little was known about element 43, except that it was an artificial radionuclide obtained by the radioactive decay of molybdenum-99. No wonder specialists from all fields joined medical institutions in the United States to participate in the exploration of its chemistry. 

The section Radioactive Methods in volume 9 of the Treatise on Analytical Chemistry (Kolthoff and Elving 1971) discusses radioactive decay, radiation detection, tracer techniques, and activation analysis. It has a brief but informative chapter on radiochemical separations. A more recent text. Nuclear and Radiochemistry Fundamentals and Applications (Lieser 2001), discusses radioelements, decay, counting instruments, nuclear reactions, radioisotope production, and activation analysis in detail. It includes a brief chapter on the chemistry of radionuclides and a few pages on the properties of the actinides and transactinides. 

Such a sequence is known as series or consecutive reactions. In this case, B is known as an intermediate because it is not the final product. A similar situation is very common in nuclear chemistry where a nuclide decays to a daughter nuclide that is also radioactive and undergoes decay (see Chapter 9). For simpficity, only the case of first-order reactions will be discussed. 

Special cases such as that arising from a nuclide decaying by more than one process simultaneously are treated exactly as the case for parallel reactions (see Chapter 2). In nuclear chemistry, this situation is referred to as branching because the overall process is taking different courses. After any given time, the ratio of the product nuclides is the same as the ratio of the decay constant producing them (see Section 2.3). However, there are some situations that arise when describing the kinetics of radioactivity that deserve special mention. 

Another subject which will be of interest for those who wish to apply nuclear chemistry for analytical purposes, is the sum peak method . The prindple of this method is based on a perturbed angular correlation (PAC) for two y-emissions in cascade decay from a radioactive nucleus. The emission angle betweoi the two y s has a distribution pattern which reflects the mode of radiative decay, as well as depetuling on the environmental conditions. The sum peak which is seen in a y-ray spectrum as a result of simultaneous detection of the twoy-rays as one event, is therefore influenced by the environments in which the source is placed. In the sum peak method, intendty ratios of the stun peak to the single peak can be used and chan in the ratios due to the environments can be observed. 

Nuclear chemistry is the study of nuclear reactions, with an emphasis on their uses in chemistry and their effects on biological systems. Nuclear chemistr) affects our lives in many ways, particularly in energy and medical applications. In radiation therapy, for example, gamma rays from a radioactive substance such as cobalt-60 are directed to cancerous tumors to destroy them. Positron emission tomography (PET) is one example of a medical diagnostic tool that relies on decay of a radioactive element injected into the body. 

Standardization matches the concept of calibration generally used in analytical chemistry. The number of radionuclides produced per unit time by irradiation of an infinitesimally thin target is determined by the balance of the increase due to nuclear reactions and the decrease due to radioactive decay ... 

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