A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state (higher energy) levels. "Metastable" describes nuclei whose excited states have half-lives 100 to 1000 times longer than the half-lives of the excited nuclear states that decay with a "prompt" half life (ordinarily on the order of 10−12 seconds). The term "metastable" is usually restricted to isomers with half-lives of 10−9 seconds or longer. Some references recommend 5 × 10−9 seconds to distinguish the metastable half life from the normal "prompt" gamma-emission half-life.[1] Occasionally the half-lives are far longer than this and can last minutes, hours, or years. For example, the 180m 73Ta nuclear isomer survives so long (at least 1015 years) that it has never been observed to decay spontaneously. The half-life of a nuclear isomer can even exceed that of the ground state of the same nuclide, as shown by 180m 73Ta as well as 186m 75Re , 192m2 77Ir , 210m 83Bi , 212m 84Po , 242m 95Am and multiple holmium isomers.
Sometimes, the gamma decay from a metastable state is referred to as isomeric transition, but this process typically resembles shorter-lived gamma decays in all external aspects with the exception of the long-lived nature of the meta-stable parent nuclear isomer. The longer lives of nuclear isomers' metastable states are often due to the larger degree of nuclear spin change which must be involved in their gamma emission to reach the ground state. This high spin change causes these decays to be forbidden transitions and delayed. Delays in emission are caused by low or high available decay energy.
The first nuclear isomer and decay-daughter system (uranium X2/uranium Z, now known as 234m 91Pa /234 91Pa ) was discovered by Otto Hahn in 1921.[2]
^Walker, Philip M.; Carroll, James J. (2007). "Nuclear Isomers: Recipes from the Past and Ingredients for the Future" (PDF). Nuclear Physics News. 17 (2): 11–15. doi:10.1080/10506890701404206. S2CID 22342780.
^Hahn, Otto (1921). "Über ein neues radioaktives Zerfallsprodukt im Uran". Die Naturwissenschaften. 9 (5): 84. Bibcode:1921NW......9...84H. doi:10.1007/BF01491321. S2CID 28599831.
A nuclearisomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy excited state (higher energy) levels...
half-lives that are less than ten minutes. One isotope, 229Th, has a nuclearisomer (or metastable state) with a remarkably low excitation energy, recently...
level. The only nuclear state suitable for the development of a nuclear clock using existing technology is thorium-229m, a nuclearisomer of thorium-229...
are a familiar example; they are isomers of carbon. Isomerism refers to the existence or possibility of isomers. Isomers do not necessarily share similar...
emission of gamma rays from excited nuclei, usually involving a specific nuclearisomer. It is analogous to conventional fluorescence, which is defined as the...
'triggering' rapid energy releases, via gamma ray emission, from a nuclearisomer of hafnium, 178m2Hf. Per event the energy release is 5 orders of magnitude...
called isomer shift) is the shift on atomic spectral lines and gamma spectral lines, which occurs as a consequence of replacement of one nuclearisomer by...
longest-lived isomer is 263mRf with a half-life of 8 seconds. mRf – Excited nuclearisomer. ( ) – Uncertainty (1σ) is given in concise form in parentheses after...
Technetium-99 is also produced as a waste product in nuclear medicine from Technetium-99m, a nuclearisomer that decays to its ground state which has no further...
"artificial", + -ium). One short-lived gamma ray-emitting nuclearisomer, technetium-99m, is used in nuclear medicine for a wide variety of tests, such as bone...
but they are as yet hindered by the scarcity and high price of this nuclearisomer. Americium is a relatively soft radioactive metal with silvery appearance...
The most common gamma emitter used in medical applications is the nuclearisomer technetium-99m which emits gamma rays in the same energy range as diagnostic...
gaps) and 2 or 3 known isomers. The longest-lived isotope is 281Ds with a half-life of 14 seconds. mDs – Excited nuclearisomer. ( ) – Uncertainty (1σ)...
to 256Cf and one nuclearisomer, 249mCf. The longest-lived isotope is 251Cf with a half-life of 898 years. mCf – Excited nuclearisomer. ( ) – Uncertainty...
releasing 8.586 MeV. Similar to its parent, it is believed to be a nuclearisomer, copernicium-285b. Due to the low beam energies associated with the...
also known, with atomic masses ranging from 9 to 23, along with three nuclearisomers. All of these radioisotopes are short-lived, the longest-lived being...
may have an even longer half-life of about 690 seconds. mBh – Excited nuclearisomer. ( ) – Uncertainty (1σ) is given in concise form in parentheses after...
design for a pure fusion weapon resulted from the DOE investment". Nuclearisomers provide a possible pathway to fissionless fusion bombs. These are naturally...
the border indicates the half-life of its nuclearisomer state. Some nuclides have multiple nuclearisomers, and this table notes the one with the longest...
longest-lived isomer is 251m1No with a half-life of 1.02 seconds. mNo – Excited nuclearisomer. ( ) – Uncertainty (1σ) is given in concise form in parentheses after...
Much smaller trace amounts of the short-lived protactinium-234 and its nuclearisomer protactinium-234m occur in the decay chain of uranium-238. Protactinium-233...
appended after the mass number to indicate a nuclearisomer, a metastable or energetically excited nuclear state (as opposed to the lowest-energy ground...
There are 39 known isotopes and 17 nuclearisomers of tellurium (52Te), with atomic masses that range from 104 to 142. These are listed in the table below...
decay of this isotope has been registered as of 2016. mHs – Excited nuclearisomer. ( ) – Uncertainty (1σ) is given in concise form in parentheses after...
by the r-process. The longest-lived isomer is 246mCm with a half-life of 1.12 seconds. mCm – Excited nuclearisomer. ( ) – Uncertainty (1σ) is given in...
500(60) yoctoseconds, corresponding to a resonance width of 910(100) keV. mF – Excited nuclearisomer. ( ) – Uncertainty (1σ) is given in concise form in parentheses after...
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