In nuclear physics, the conversion of one nuclide to another, either by natural radioactive decay or by collision with other nuclei or particles. Loosely, one element can thus be transmuted into another. Alchemy failed, since it attempted to manipulate only chemical properties, not the nucleus, which is what controls the element's type. The first artificial transmutation was achieved by Ernest Rutherford, who in 1919 turned nitrogen into oxygen.
Transmutation of chemical elements occurs through nuclear reactions. Natural transmutation is when radioactive elements spontaneously decay over a long period of time and transform into other more stable elements. Artificial transmutation occurs in machinery that has enough energy to cause changes in nuclear structure of the elements. The machines that can cause artificial transmutation include the particle accelerator and tokamak reactor.Photoneutron process
Transmutation of the elements can occur naturally or artificially by the photoneutron process. A Gamma ray (high-energy photon) with an energy greater than the neutron binding force can eject a neutron from a stable nucleus to cause transmutation to another element. The Spallation Neutron Source completed in 2006 at Oak Ridge National Laboratory causes transmutation of Mercury to Gold and other precious metals below Gold in atomic mass.[]
Origin
The term dates back to the search for the philosopher's stone.
Overview
Transmutation of transuranium elements (actinides) such as the isotopes of plutonium, neptunium, americium, and curium has the potential to help solve the problems posed by the management of radioactive waste, by reducing the proportion of long-lived isotopes it contains. When irradiated with neutrons in a nuclear reactor, these isotopes can be made to undergo nuclear fission, destroying the original actinide isotope and producing a spectrum of radioactive and nonradioactive fission products.
Reactor types
For instance, plutonium can be reprocessed into MOX fuels and transmuted in standard reactors. The heavier elements could be transmuted in fast reactors, but probably more effectively in a subcritical reactor which is sometimes known as an energy amplifier and which was devised by Carlo Rubbia.
Reasoning behind transmutation
Isotopes of plutonium and other actinides tend to be long-lived with half-lives of many thousands of years, whereas radioactive fission products tend to be shorter-lived (most with half-lives of 30 years or less). From a waste management viewpoint, transmutation of actinides eliminates a very long-term radioactive hazard and replaces it with a much shorter-term one.
It is important to understand that the threat posed by a radioisotope is influenced by many factors including the chemical and biological properties of the element.
Many of the actinides are very radiotoxic because they have long biological half-lives and are alpha emitters. In transmutation the intention is to convert the actinides into fission products. The most worrying shortlived fission products are those that accumulate in the body, such as iodine-131 which accumulates in the thyroid gland, but it is hoped that by good design of the nuclear fuel and transmutation plant that such fission products can be isolated from man and his environment and allowed to decay.
In stars
Gold is actually created by supernovae, which however transmute a lot of it into lead - a much easier process. The alchemical belief in transmutation was based on a thoroughly wrong understanding of the underlying processes.
Genuine scientific transmutation is nicely described in Ken Croswell's book The Alchemy of the Heavens. He summarised the process as:
This summarises Synthesis of the Elements in Stars (Reviews of Modern Physics, vol.
Alchemy
In alchemy, it is believed that such transformations can be accomplished in table-top experiments and some researchers say they have found evidence of transmutation of elements in biological processes (see Kervran).
Modern nuclear experiments have successfully transmuted lead into gold.
Au (half life 2.7 days) -->
User Comments Add a comment…
3 months ago
I am interested in the concept of transmutation but could you explain how ejecting a neutron from the nucleus transmutates the atom? Isn't the atom defined by the number of protons it has?