Editing Metastability (section)

===Nuclear physics===
Some energetic states of an [[atomic nucleus]] (having distinct spatial mass, charge, spin, [[isospin]] distributions) are much longer-lived than others ([[nuclear isomer#Metastable isomers|nuclear isomers]] of the same [[isotope]]), e.g. [[technetium-99m]].<ref>{{cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/technetium.html|title=Technetium-99m |publisher=Hyperphysics}}</ref> The isotope [[isotopes of tantalum#Tantalum-180m|tantalum-180m]], although being a metastable excited state, is long-lived enough that it has never been observed to decay, with a half-life calculated to be least {{val|4.5|e=16}} years,<ref>{{cite web|url=https://www.sciencenews.org/article/rarest-nucleus-reluctant-decay|title=Rarest nucleus reluctant to decay|last=Conover|first=Emily|date=2016-10-03 |website=Science News |access-date=2016-10-05}}</ref><ref>{{cite journal|last1=Lehnert|first1=Björn|last2=Hult|first2=Mikael|last3=Lutter|first3=Guillaume|last4=Zuber|first4=Kai|year=2017|title=Search for the decay of nature's rarest isotope <sup>180m</sup>Ta|arxiv=1609.03725|doi=10.1103/PhysRevC.95.044306|volume=95|pages=044306|journal=Physical Review C|issue=4 |bibcode=2017PhRvC..95d4306L|s2cid=118497863 }}</ref> over 3 million times the current [[age of the universe]].