Editing Terbium (section)

=== Isotopes ===
{{Main|Isotopes of terbium}}
Naturally occurring terbium is composed of its only stable [[isotope]], terbium-159; the element is thus [[mononuclidic element|mononuclidic]] and [[monoisotopic element|monoisotopic]].<ref name="CIAAWterbium"/> Thirty-nine [[radioisotope]]s have been characterized,{{AME2020 II|ref}} with the heaviest being terbium-174 and lightest being terbium-135 (both with unknown exact mass).{{NUBASE2020|ref}} The most stable [[synthetic radioisotope]]s of terbium are terbium-158, with a [[half-life]] of 180 years, and terbium-157, with a half-life of 71 years. All of the remaining [[radioactive]] isotopes have half-lives that are less than three months, and the majority of these have half-lives that are less than half a minute.{{NUBASE2020|ref}} The primary [[decay mode]] before the most abundant stable isotope, {{sup|159}}Tb, is [[electron capture]], which results in production of [[gadolinium]] isotopes, and the primary mode after is [[beta minus decay]], resulting in [[dysprosium]] isotopes.{{NUBASE2020|ref}}

The element also has 31 [[nuclear isomer]]s, with masses of 141–154, 156, 158, 162, and 164–168 (not every mass number corresponds to only one isomer).{{AME2020 II|ref}} The most stable of them are terbium-156m, with a half-life of 24.4 hours, and terbium-156m2, with a half-life of 22.7 hours; this is longer than half-lives of most ground states of radioactive terbium isotopes, except those with mass numbers 155–161.{{NUBASE2020|ref}}

Terbium-149, with a half-life of 4.1 hours, is a promising candidate in [[targeted alpha therapy]] and [[positron emission tomography]].<ref>{{cite journal | last1=Müller | first1=Cristina | last2=Vermeulen | first2=Christiaan | last3=Köster | first3=Ulli | last4=Johnston | first4=Karl | last5=Türler | first5=Andreas | last6=Schibli | first6=Roger | last7=van der Meulen | first7=Nicholas P. | title=Alpha-PET with terbium-149: evidence and perspectives for radiotheragnostics | journal=EJNMMI Radiopharmacy and Chemistry | publisher=Springer Science and Business Media LLC | volume=1 | issue=1 | date=2016-03-28 | page=5 | issn=2365-421X | doi=10.1186/s41181-016-0008-2| pmid=29564382 | pmc=5843804 | doi-access=free }}</ref><ref>{{cite journal | last1=Eychenne | first1=Romain | last2=Chérel | first2=Michel | last3=Haddad | first3=Férid | last4=Guérard | first4=François | last5=Gestin | first5=Jean-François | title=Overview of the Most Promising Radionuclides for Targeted Alpha Therapy: The "Hopeful Eight" | journal=Pharmaceutics | publisher=MDPI AG | volume=13 | issue=6 | date=2021-06-18 | issn=1999-4923 | doi=10.3390/pharmaceutics13060906 | page=906 | pmid=34207408 | pmc=8234975 | doi-access=free }}</ref>