Radioactive atoms

A recoil-implanted metal atom (radioactive M) undergoes the following chemical reaction with a metal coordination compound in a film of catcher material ... 

TRANSMUTATION. The natural or artificial transformation of atoms of one element into atoms of a different element as the result of a nuclear reaction. The reaction may be one in which two nuclei interact, as in the formation of oxygen from nitrogen and helium nuclei (/3-particles), or one in which a nucleus reacts widi an elementary particle such as a neutron or proton. Thus, a sodium atom and a proton form a magnesium atom. Radioactive decay, e.g., of uranium, can be regarded as a type of transmutation. The first transmutation was performed bv the English physicist Rutherford in 1919. 

A nuclide containing numbers of protons and neutrons that place it outside this band of stability will be unstable until it undergoes one or more nuclear reactions that take it into the band of stability. We call these unstable atoms radioactive nuclides, and the changes they undergo to reach stability are called radioactive decay. Note that the band of stability stops at 83 protons. All of the known nuclides with more than 83 protons are radioactive, but scientists have postulated that there should be a small island of stability around the point representing 114 protons and 184 neutrons. The relative stability of the heaviest atoms that have so far been synthesized in the laboratory suggests that this is true. (See Special Topic 2.1 Why Create New Elements.)-... 

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. 

Radioactivity is caused by changes in the nucleus of the atom. Radioactivity is not a chemical activity, but rather it is a nuclear event. Chemical activity involves electrons orbiting around the nucleus of an atom, particularly the outer-shell electrons. It is within these outer-shell electrons that chemical reactions and chemical bonding take place. Radioactivity, on the other hand, involves the nucleus of the atom. There is normally a strong force that holds the nucleus of an atom together. 

The carbon-12 isotope with 6 protons and 6 neutrons in its nucleus, gC, constitutes 98.9% of all naturally occurring carbon. The gC isotope makes up 1.1% of all carbon atoms. Radioactive carbon-14, gC, is present in some carbon sources. 

As a common consequence of any interaction of nuclear radiation with matter, electron vacancies are created in the K, L, M shells of the atoms. Radioactive decay can also create vacancies in the daughter atoms (electron capture, internal conversion). Electron vacancies can cause X-ray transitions or - as shown by Auger (1925) - the vacancy is filled at the expense of a shell electron emission with the energy... 

To investigate the origin of the isonitrile carbon atoms, radioactive substances known to be Cj-precursors were added to xanthocillin-producing cultures. Surprisingly, there was no radioactivity incorporated either from methionine- CHg or from formate- C, a result which indicates that the isonitrile carbons do not... 

There are other less common types of radioactive decay. Positron emission results in a decrease by one unit in the atomic number K capture involves the incorporation of one of the extranuclear electrons into the nucleus, the atomic number is again decreased by one unit. 

All elements of atomic number greater than 83 exhibit radioactive decay K, Rb, Ir and a few other light elements emit p particles. The heavy elements decay through various isotopes until a stable nucleus is reached. Known half-lives range from seconds to 10 years. 

Radioactive elements may often be prepared artificially by bombarding the atoms of ordinary stable elements with, e.g. helium nuclei. See radioactivity, artificial. 

Classic examples are the spontaneous emission of light or spontaneous radioactive decay. In chemistry, an important class of monomolecular reactions is the predissociation of metastable (excited) species. An example is the fonnation of oxygen atoms in the upper atmosphere by predissociation of electronically excited O2 molecules [12, 13 and 14] ... 

Deuterium is used as a moderator to slow down neutrons. Tritium atoms are also present but in much smaller proportions. Tritium is readily produced in nuclear reactors and is used in the production of the hydrogen (fusion) bomb. It is also used as a radioactive agent in making luminous paints, and as a tracer. 

How many carbon atoms of citronellal would be radioactively labeled if the acetic acid used in the experiment were enriched with at C 1 instead of at C 2 Identify these carbon atoms... 

The data were extracted from M. Lederer and V. S. Shirley, Table of Isotopes, 7th ed., Wiley-Interscience, New York, 1978 A. H. Wapstra and G. Audi, The 1983 Atomic Mass Evaluation, Nucl. Phys. A432 l-54 (1985) V. S. Shirley, ed.. Table of Radioactive Isotopes, 8th ed., Wiley-Interscience, New York, 1986 and P. Raghavan, Table of Nuclear Moments, At. Data Nucl. Data Tables, 42 189 (1989). 

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol E, where E is the element s atomic symbol, Z is the element s atomic number (which is the number of protons), and A is the element s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form. 

The most important types of radioactive particles are alpha particles, beta particles, gamma rays, and X-rays. An alpha particle, which is symbolized as a, is equivalent to a helium nucleus, fHe. Thus, emission of an alpha particle results in a new isotope whose atomic number and atomic mass number are, respectively, 2 and 4 less than that for the unstable parent isotope. 

By measuring the activity at time f, therefore, we can determine the initial activity, Aq, or the number of radioactive atoms originally present in the sample, Nq. 

An important characteristic property of a radioactive isotope is its half-life, fj/2, which is the amount of time required for half of the radioactive atoms to disintegrate. For first-order kinetics the half-life is independent of concentration and is given as... 

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