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EXPLANATION An Isotope , is an element 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 or 58mCo). STABLE ISOMERS 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 Supernova s. When it relaxes to its base state, it releases energetic Photon s with wavelength of 16 Nanometers — X-ray Wavelength s. 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 Hafnium -178m, which has the highest excitation energy of any stable isomer. One Kilogram of pure Hf-178-2m would contain approximately 900 Megajoule s(?) of energy, the equivalent of about 226 kilograms (500 pounds) of TNT . Further, ''all'' of the energy released is in Gamma Ray s 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 Laser s ( GRASER s). 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 Exawatt s). As Of 2005 the claims that hafnium isomers can be used as potential energy storage devices or even weapons is generally regarded with derision in the general scientific community and future prospects for the idea's vindication appear very dim. Technetium isomers Tc-99m (with a half-life of 6.01 hours) and Tc-95m (with a half-life of 61 days) are used in Medical and Industrial applications. APPLICATIONS These hafnium and tantalum isomers have been considered in some quarters as weapons that could be used to circumvent the Nuclear Non-Proliferation Treaty , since they can be induced to very strongly emit gamma radiation. DARPA does now or has had a program to investigate this usage of both isomers. However, given the difference in speed between a photon and a neutron, they can't be induced to chain react like a nuclear weapon, so there will probably never be such a weapon. Ta-180m is also one of the most expensive substance to procure in the world, at approximately $17 million per gram. In 1999, the entire world's supply of Ta-180m was only 6.7 milligrams. DECAY PROCESSES They decay to lower energy states of the nuclide through two Isomeric Transitions :
SEE ALSO EXTERNAL LINKS
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