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A nuclear isomer is a metastable state of an atom caused by the excitation of a proton or neutron in its nucleus so that it requires a change in spin before it can release its extra energy. Contrast this with the definition of a chemical isomer, the more common use of the word. Also contrast with the meaning of isotope, in which the difference is the number of neutrons in the nucleus. Metastable isomers of a particular atom are usually designated with an "m" (or, in the case of atoms with more than one isomer, 2m, 3m, and so on). This designation is usually placed after the atomic symbol and number of the atom (e.g., Co-58m), but is sometimes placed as a superscript before (e.g., mCo-58).Most nuclear isomers are very unstable, and radiate away the extra energy immediately (on the order of 10-12 seconds). As a result, the term is usually restricted to mean isomers with half-lives of 10-9 seconds or more. Quantum mechanics predicts that certain atomic species will possess isomers with unusually long lifetimes even by this stricter standard, and so have interesting properties.
The only stable nuclear isomer is Ta-180m, which occurs naturally in tantalum at about 1 part in 8300. Its half-life is at least 1015 years, and it may in fact be entirely stable. The origin of this isomer is mysterious, though it is believed to have something to do with supernovas. When it relaxes to its base state, it releases energetic photons with wavelength of 16 nanometers— x-ray wavelengthThe wavelength is the distance between repeating units of a wave pattern. It is commonly designated by the greek letter lambda (λ). In a sine wave, the wavelength is the distance between peaks: The x axis represents distance, and I would be some vas. There are reports that Ta-180m can be forced to release its energy by much weaker x-rays, but these are currently in scientific dispute.
Another reasonably stable nuclear isomer (with a half-life of 31 years) is hafniumHafnium is a chemical element in the periodic table that has the symbol Hf and atomic number 72. A lustrous, silvery gray tetravalent transition metal, hafnium resembles zirconium chemically and is found in zirconium minerals. Hafnium is used in tungsten-178m, which has the highest excitation energy of any stable isomer. One kilogramThe kilogram (symbol: kg is the SI base unit of mass. A gram is defined as one thousandth of a kilogram. Conversion of units describes equivalent units of mass in other systems. Multiples SI prefixes are used to name multiples and subdivisions of the kilo of pure Hf-178-2m contains approximately 900 gigajouleThe joule (symbol J also called newton metre or coulomb volt is the SI unit of energy and work. The unit is pronounced to rhyme with "tool", and is named in honour of the physicist James Prescott Joule (1818-1889). 1 joule 1 N · 1 m 1 newton · 1 metre 1 ks of energy, or about a quarter of a kiloton. Further, all of the energy released is in gamma rayThis article is about electromagnatic radiation. For the power metal band, see Gamma Ray (band Gamma rays (often denoted by the Greek letter gamma, γ) are an energetic form of electromagnetic radiation (see Electromagnetic spectrum) produced by radis at 0.05 nanometers. As with Ta-180m, there are disputed reports that Hf-178-2m can be stimulated into releasing its energy, and as a result the substance is being studied as a possible source for gamma ray laserFor alternative meanings see laser (disambiguation). A laser light amplification by stimulated emission of radiation is a device which uses a quantum mechanical effect, stimulated emission, to generate a coherent beam of light. Light from a laser is oftens. These reports also indicate that the energy is released very quickly, so that Hf-178-2m can produce extremely high powers (on the order of exawattThe watt (symbol: W is the SI derived unit for power. It is equivalent to 1 joule per second (1 J/s), or in electrical units, 1 volt- ampere (1 V · A). It is the rate in joules per second at which energy is being converted, used or dissipated. Equations :s).
Both of these isomers, as well as others, are currently being explored as a means of energy storage, as it is possible to "pump" standard atoms of the type into their higher states. However, all currently known methods of doing so are very inefficient, and knowledge of how to trigger a release of energy is still in its infancy.
