Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of another element by a process which occurs either through nuclear reactions (in which an outside particle reacts with a nucleus), or through radioactive decay (where no outside particle is needed). Transmutation technology has the potential to greatly reduce the long-term negative effects of radioactive wastes on human populations by reducing its radioactive half-life.[1] Not all radioactive decay or nuclear reactions cause transmutation, but all transmutation is caused by either decay or nuclear reaction. The most common types of radioactive decay that do not cause transmutation are gamma decay and the related process internal conversion. However, most other types of decay do cause transmutation of the decaying radioisotope. Similarly, a few nuclear reactions do not cause transmutation (for example the gain or loss of a neutron might not cause transmutation), although in practice, most nuclear reactions, and types of nuclear re the creation of all the chemical elements we observe naturally. Most of this happened in the distant past, however (see section below on transmutation in the universe). One type of natural transmutation observable in the present occurs when certain radioactive elements present in nature spontaneously decay by a process that causes transmutation, such as alpha or beta decay. An example is the natural decay of potassium-40 to the argon-40, which forms most of the argon in air. Also on Earth, natural transmutations from the different mechanism of natural nuclear reactions occur, due to cosmic ray bombardment of elements (for example, to form carbon-14), and also occasionally from natural neutron bombardment (for example, see natural nuclear fission reactor). Artificial transmutation may occur in machinery that has enough energy to cause changes in the nuclear structure of the elements. Machines that can cause artificial transmutation include particle accelerators and tokamak reactors. Conventional fission power reactors also cause artificial transmutation, not from the power of the machine, but by exposing elements to neutrons produced by a fission from an artificially produced nuclear chain reaction. Artificial nuclear transmutation has been considered as a possible mechanism for reducing the volume and hazard of radioactive waste. Contents [hide] 1 History 2 Transmutation in the universe 3 Artificial transmutation of nuclear waste 3.1 Overview 3.2 Reactor types 3.3 Fuel types 3.4 Reasoning behind transmutation 3.5 Long-lived fission products 4 See also 5 External links 6 References History[edit] The term transmutation dates back to alchemy. Alchemists pursued the philosophers stone, capable of chrysopoeia – the transformation of base metals into gold. While alchemists often understood chrysopoeia as a metaphor for a mystical, or religious process, some practitioners adopted a literal interpretation, and tried to make gold through physical experiment. The impossibility of the metallic transmutation had been debated amongst alchemists, philosophers and scientists since the Middle Ages. Pseudo-alchemical transmutation was outlawed[2] and publicly mocked beginning in the fourteenth century. Alchemists like Michael Maier and Heinrich Khunrath wrote tracts exposing fraudulent claims of gold making. By the 1720s, there were no longer any respectable figures pursuing the physical transmutation of substances into gold.[3] Antoine Lavoisier, in the 18th century, replaced the alchemical theory of elements with the modern theory of chemical elements, and John Dalton further developed the notion of atoms (from the alchemical theory of corpuscles) to explain various chemical processes. The disintegration of atoms is a distinct process involving much greater energies than could be achieved by alchemists. It was first consciously applied to modern physics by Frederick Soddy when he, along with Ernest Rutherford, discovered that radioactive thorium was converting itself into radium in 1901. At the moment of realization, Soddy later recalled, he shouted out: Rutherford, this is transmutation! Rutherford snapped back, For Christs sake, Soddy, dont call it transmutation. Theyll have our heads off as alchemists.[4] Rutherford and Soddy were observing natural transmutation as a part of radioactive decay of the alpha decay type. However in 1919, Rutherford was able to accomplish transmutation of nitrogen into oxygen, using alpha particles directed at nitrogen 14N + α → 17O + p. This was the first observation of a nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. Eventually, in 1932, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherfords colleagues John Cockcroft and Ernest Walton, who used artificially accelerated protons against lithium-7 to split the nucleus into two alpha particles. The feat was popularly known as splitting the atom, although it was not the modern nuclear fission reaction discovered in 1938 by Otto Hahn, Lise Meitner and their assistant Fritz Strassmann in heavy elements.[5] Later in the twentieth century the transmutation of elements within stars was elaborated, accounting for the relative abundance of heavier elements in the universe. Save for the first five elements, which were produced in the Big Bang and other cosmic ray processes, stellar nucleosynthesis accounted for the abundance of all elements heavier than boron. In their 1957 paper Synthesis of the Elements in Stars,[6] William Alfred Fowler, Margaret Burbidge, Geoffrey Burbidge, and Fred Hoyle explained how the abundances of essentially all but the lightest chemical elements could be explained by the process of nucleosynthesis in stars. It transpired that, under true nuclear transmutation, it is far easier to turn gold into lead than the reverse reaction, which was the one the alchemists had ardently pursued. Nuclear experiments have successfully transmuted lead into gold, but the expense far exceeds any gain.[7] It would be easier to convert gold into lead via neutron capture and beta decay by leaving gold in a nuclear reactor for a long period of time. Glenn Seaborg produced several thousand atoms of gold from bismuth, but at a net loss. More information on gold synthesis, see Synthesis of precious metals.
Posted on: Tue, 11 Nov 2014 23:49:40 +0000
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