Editing Nuclear isomer (section)

==Nearly stable isomers==
Most nuclear excited states are very unstable and "immediately" radiate away the extra energy after existing on the order of 10<sup>−12</sup>&nbsp;seconds. As a result, the characterization "nuclear isomer" is usually applied only to configurations with half-lives of 10<sup>−9</sup>&nbsp;seconds or longer. [[Quantum mechanics]] predicts that certain atomic species should possess isomers with unusually long lifetimes even by this stricter standard and have interesting properties. Some nuclear isomers are so long-lived that they are relatively stable and can be produced and observed in quantity.

The most stable nuclear isomer occurring in nature is [[tantalum-180m|{{nuclide|Ta|180|m}}]], which is present in all [[tantalum]] samples at about 1 part in 8,300. Its half-life is theorized to be at least {{val|2.9|e=17}} years, markedly longer than the [[age of the universe]]. The low excitation energy of the isomeric state causes both gamma de-excitation to the {{SimpleNuclide|Ta|180}} ground state (which itself is radioactive by beta decay, with a half-life of only 8 hours) and direct [[electron capture]] to [[hafnium]] or [[beta decay]] to [[tungsten]] to be suppressed due to spin mismatches. The origin of this isomer is mysterious, though it is believed to have been formed in [[supernova]]e (as are most other heavy elements). Were it to relax to its ground state, it would release a [[photon]] with a [[photon energy]] of 75&nbsp;[[Electronvolt|keV]].

It was first reported in 1988 by C. B. Collins<!--he's not the C. B. Collins with an article, so don't link--><ref>{{cite journal | author=C. B. Collins | title=Depopulation of the isomeric state <sup>180</sup>Ta<sup>m</sup> by the reaction <sup>180</sup>Ta<sup>m</sup>(γ,γ′)<sup>180</sup>Ta | url=http://www.hafniumisomer.org/isomer/180ta.pdf | journal= Physical Review C | volume=37 | pages=2267–2269 | year=1988 | doi=10.1103/PhysRevC.37.2267 | bibcode = 1988PhRvC..37.2267C | issue=5 | pmid=9954706 |display-authors=etal |url-status=dead |archive-url=https://web.archive.org/web/20190121175916/http://www.hafniumisomer.org/isomer/180ta.pdf |archive-date=21 January 2019}}</ref> that theoretically {{SimpleNuclide|Ta|180|m}} can be forced to release its energy by weaker X-rays, although at that time this de-excitation mechanism had never been observed. However, the de-excitation of {{SimpleNuclide|Ta|180|m}} by resonant photo-excitation of intermediate high levels of this nucleus (''E''&nbsp;≈&nbsp;1&nbsp;MeV) was  observed in 1999 by Belic and co-workers in the Stuttgart nuclear physics group.<ref>{{cite journal | author=D. Belic | title=Photoactivation of <sup>180</sup>Ta<sup>m</sup> and Its Implications for the Nucleosynthesis of Nature's Rarest Naturally Occurring Isotope | journal= Physical Review Letters | volume=83 | issue=25 | pages=5242–5245 | year=1999 | doi =10.1103/PhysRevLett.83.5242 | bibcode=1999PhRvL..83.5242B | display-authors=etal}}</ref>

[[hafnium-178|{{nuclide|Hf|178|m2}}]] is another reasonably stable nuclear isomer. It possesses a half-life of 31 years and the highest excitation energy of any comparably long-lived isomer. One [[gram]] of pure {{SimpleNuclide|Hf|178|m2}} contains approximately 1.33 gigajoules of energy, the equivalent of exploding about {{cvt|315|kg|lb|-2}} of [[TNT equivalent|TNT]]. In the natural decay of {{SimpleNuclide|Hf|178|m2}}, the energy is released as gamma rays with a total energy of 2.45&nbsp;MeV. As with {{SimpleNuclide|Ta|180|m}}, there are disputed reports that {{SimpleNuclide|Hf|178|m2}} can be [[stimulated emission|stimulated]] into releasing its energy. Due to this, the substance is being studied as a possible source for [[gamma-ray laser]]s. These reports indicate that the energy is released very quickly, so that {{SimpleNuclide|Hf|178|m2}} can produce extremely high powers (on the order of [[Orders of magnitude (power)|exawatts]]). Other isomers have also been investigated as possible media for [[Induced gamma emission|gamma-ray stimulated emission]].<ref name=Walker/><ref>{{cite web | title=UNH researchers search for stimulated gamma ray emission | url=http://einstein.unh.edu/nuclear/NucNews/graser_news.html | website=UNH Nuclear Physics Group | year=1997 | access-date=1 June 2006 |archive-url = https://web.archive.org/web/20060905160103/http://einstein.unh.edu/nuclear/NucNews/graser_news.html |archive-date = 5 September 2006}}</ref>

[[Holmium]]'s nuclear isomer [[holmium-166|{{nuclide|Holmium|166|m1}}]] has a half-life of 1,200 years, which is nearly the longest half-life of any holmium radionuclide. Only {{SimpleNuclide|Holmium|163}}, with a half-life of 4,570 years, is more stable.

[[thorium-229|{{nuclide|Thorium|229}}]] has a remarkably low-lying metastable isomer only {{val|{{#expr:(2020407384335*6.62607015/1.602176634e12) round 12}}|(8)|u=eV}} above the ground state.<ref name=Tiedau2024>{{Cite journal
| last=Tiedau | first=J.
| last2=Okhapkin | first2=M. V.
| last3=Zhang | first3=K.
| last4=Thielking | first4=J.
| last5=Zitzer | first5=G.
| last6=Peik | first6=E.
| last7=Schaden | first7=F.
| last8=Pronebner | first8=T.
| last9=Morawetz | first9=I.
| last10=De Col | first10=L. Toscani
| last11=Schneider | first11=F.
| last12=Leitner | first12=A.
| last13=Pressler | first13=M.
| last14=Kazakov | first14=G. A.
| last15=Beeks | first15=K.
| date=2024-04-29
| title=Laser Excitation of the Th-229 Nucleus
| url=https://link.aps.org/doi/10.1103/PhysRevLett.132.182501
| journal=Physical Review Letters
| volume=132 | issue=18 | article-number=182501
| doi=10.1103/PhysRevLett.132.182501
| doi-access=free
}}</ref><ref name=Zhang2024>{{cite journal
 |title=Frequency ratio of the <sup>229m</sup>Th nuclear isomeric transition and the <sup>87</sup>Sr atomic clock
 |first1=Chuankun |last1=Zhang  |first2=Tian |last2=Ooi  |first3=Jacob S. |last3=Higgins
 |first4=Jack F. |last4=Doyle  |first5=Lars |last5=von der Wense  |first6=Kjeld |last6=Beeks
 |first7=Adrian |last7=Leitner  |first8=Georgy |last8=Kazakov  |first9=Peng |last9=Li
 |first10=Peter G. |last10=Thirolf  |first11=Thorsten |last11=Schumm  |first12=Jun |last12=Ye |author-link12=Jun Ye
 |journal=[[Nature (journal)|Nature]] |volume=633 |issue=8028 |pages=63–70
 |date=4 September 2024
 |doi=10.1038/s41586-024-07839-6
 |pmid=39232152 |arxiv=2406.18719
 |quote=The transition frequency between the {{math|1=''I'' = 5/2}} ground state and the {{math|1=''I'' = 3/2}} excited state is determined as: {{math|1=
''𝜈''<sub>Th</sub> = {{sfrac|1|6}} (''𝜈''<sub>a</sub> + 2''𝜈''<sub>b</sub> + 2''𝜈''<sub>c</sub> + ''𝜈''<sub>d</sub>) = {{val|2020407384335|(2)|u=kHz}}}}.
}}</ref><ref name=Conover2024>{{cite news
 |title=A nuclear clock prototype hints at ultraprecise timekeeping
 |first=Emily |last=Conover |author-link=Emily Conover 
 |date=4 September 2024
 |journal=[[ScienceNews]]
 |url=https://www.sciencenews.org/article/nuclear-clock-ultraprecise-timekeeping
}}</ref>  This low energy produces "gamma rays" at a wavelength of {{val|{{#expr:(299792458e6/2020407384335) round 10}}|(15)|u=nm}}, in the [[far ultraviolet]], which allows for direct nuclear laser [[spectroscopy]].  Such ultra-precise spectroscopy, however, could not begin without a sufficiently precise initial estimate of the wavelength, something that was only achieved in 2024 after two decades<!--2003 to 2024--> of effort.<ref>{{cite journal 
| journal=[[Nature (journal)|Nature]]
| volume=533 | issue=7601 | pages=47–51
| date=2016-05-05
| title=Direct detection of the <sup>229</sup>Th nuclear clock transition
| first1=Lars | last1=von der Wense
| first2=Benedict | last2=Seiferle
| first3=Mustapha | last3=Laatiaoui
| first4=Jürgen B. | last4=Neumayr
| first5=Hans-Jörg | last5=Maier
| first6=Hans-Friedrich | last6=Wirth
| first7=Christoph | last7=Mokry
| first8=Jörg | last8=Runke
| first9=Klaus | last9=Eberhardt
| first10=Christoph E. | last10=Düllmann
| first11=Norbert G. | last11=Trautmann
| first12=Peter G. | last12=Thirolf
| doi=10.1038/nature17669
| pmid=27147026 | url=http://www.2physics.com/2016/06/direct-detection-of-229-th-nuclear.html
| bibcode=2016Natur.533...47V |arxiv=1710.11398| s2cid=205248786 }}</ref><ref>{{Cite press release
| url=http://www.med.physik.uni-muenchen.de/aktuelles/nature-229-thorium/index.html
| title=Results on <sup>229m</sup>Thorium published in "Nature"
| publisher=[[Ludwig Maximilian University of Munich]]
| date=2016-05-06
| access-date=1 August 2016
| archive-url=https://web.archive.org/web/20160827161042/http://www.med.physik.uni-muenchen.de/aktuelles/nature-229-thorium/index.html
| archive-date=27 August 2016
| url-status=dead
}}</ref><ref>{{cite journal
| last1=Seiferle |first1=B. |last2=von der Wense |first2=L. |last3=Thirolf |first3=P.G.
| title = Lifetime measurement of the <sup>229</sup>Th nuclear isomer  
| journal = Phys. Rev. Lett.
| volume = 118 | issue=4 | article-number = 042501
| date = 2017-01-26
| doi = 10.1103/PhysRevLett.118.042501
|pmid=28186791 | arxiv=1801.05205
|s2cid=37518294 }}</ref><ref>{{cite journal
| last1=Thielking |first1=J.
| last2=Okhapkin |first2=M.V.
| last3=Przemyslaw |first3=G.
| last4=Meier |first4=D.M.
| last5=von der Wense |first5=L.
| last6=Seiferle |first6=B.
| last7=Düllmann |first7=C.E.
| last8=Thirolf |first8=P.G.
| last9=Peik |first9=E.
| title = Laser spectroscopic characterization of the nuclear-clock isomer <sup>229m</sup>Th
| journal = Nature
| volume = 556 | issue=7701 | pages = 321–325
| year = 2018
| doi = 10.1038/s41586-018-0011-8
| pmid=29670266 | arxiv=1709.05325
|s2cid=4990345
}}</ref><ref name="SeiferleEnergy">{{cite journal
| title = Energy of the <sup>229</sup>Th nuclear clock transition
| journal=[[Nature (journal)|Nature]]
| volume=573  | issue=7773 | pages=243–246
| date=2019-09-12
| first1=B. |last1=Seiferle
| first2=L. |last2=von der Wense
| first3=P.V.  |last3=Bilous
| first4=I. |last4=Amersdorffer
| first5=C. |last5=Lemell
| first6=F. |last6=Libisch
| first7=S. |last7=Stellmer
| first8=T. |last8=Schumm
| first9=C.E. |last9=Düllmann
| first10=A. |last10=Pálffy
| first11=P.G. |last11=Thirolf
| doi=10.1038/s41586-019-1533-4
| pmid=31511684
| arxiv=1905.06308
 | s2cid=155090121
}}</ref><ref name=Zhang2024/> The energy is so low that the ionization state of the atom affects its half-life.  Neutral {{nuclide|Thorium|229|m}} decays by [[internal conversion]] with a half-life of {{val|7|1|u=us}}, but because the isomeric energy is less than thorium's second ionization energy of {{val|11.5|u=eV}}, this channel is forbidden in thorium [[cations]] and {{nuclide|Thorium|229|m|charge=+}} decays by gamma emission with a half-life of {{val|1740|50|u=s}}.{{r|Tiedau2024}}  This conveniently moderate lifetime allows the development of a [[nuclear clock]] of unprecedented accuracy.<ref name="Peik2003">{{cite journal
| first1 = Ekkehard 
| last1 = Peik
| first2 = Christian
| last2 = Tamm
| title = Nuclear laser spectroscopy of the 3.5&nbsp;eV transition in <sup>229</sup>Th
| url = http://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_4/4.4_zeit_und_frequenz/pdf/th001.pdf
| journal = Europhysics Letters
| volume = 61
| issue = 2
| pages = 181–186
| date = 2003-01-15
| doi = 10.1209/epl/i2003-00210-x
| bibcode = 2003EL.....61..181P
| s2cid = 250818523
| access-date = 12 September 2019
| archive-url = https://web.archive.org/web/20131216161909/http://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_4/4.4_zeit_und_frequenz/pdf/th001.pdf
| archive-date = 16 December 2013
| url-status = dead
}}</ref><ref name="Campbell2012">{{cite journal
| first1=C.   |last1=Campbell
| first2=A.G. |last2=Radnaev
| first3=A.   |last3=Kuzmich
| first4=V.A. |last4=Dzuba
| first5=V.V. |last5=Flambaum
| first6=A.   |last6=Derevianko
| title = A single ion nuclear clock for metrology at the 19th decimal place
| journal = Phys. Rev. Lett.
| volume = 108 | issue=12
| article-number = 120802
| date = 22 March 2012
| doi = 10.1103/PhysRevLett.108.120802
| pmid=22540568
| arxiv= 1110.2490
| url=https://link.aps.org/accepted/10.1103/PhysRevLett.108.120802
|bibcode=2012PhRvL.108l0802C
|s2cid=40863227
}}</ref><ref name=Conover2024/>