Editing Tantalum (section)

==Characteristics==

===Physical properties===
Tantalum is dark (blue-gray),<ref>{{cite book | chapter = Tantalum | chapter-url = https://books.google.com/books?id=5o3Lr2Swz8sC&pg=PA204 | isbn = 978-0-86516-573-1 | title = Classical Mythology & More: A Reader Workbook | author1 = Colakis, Marianthe | author2 = Masello, Mary Joan | date = 2007-06-30| publisher=Bolchazy-Carducci Publishers }}</ref> dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is highly resistant to [[corrosion]] by [[acid]]s: at temperatures below 150&nbsp;°[[Celsius|C]] tantalum is almost completely immune to attack by the normally aggressive [[aqua regia]]. It can be dissolved with [[hydrofluoric acid]] or acidic solutions containing the [[fluoride]] ion and [[sulfur trioxide]], as well as with molten [[potassium hydroxide]]. Tantalum's high melting point of 3017&nbsp;°C (boiling point 5458&nbsp;°C) is exceeded among the elements only by [[tungsten]], [[rhenium]], and [[osmium]] for metals, and [[carbon]].

Tantalum exists in two crystalline phases, alpha and beta. The alpha phase is stable at all temperatures up to the melting point and has [[body-centered cubic]] structure with lattice constant ''a'' = 0.33029&nbsp;nm at 20&nbsp;°C.<ref name="Arblaster 2018" /> It is relatively [[Ductility|ductile]], has [[Knoop hardness test|Knoop hardness]] 200–400 HN and electrical resistivity 15–60 μΩ⋅cm. The beta phase is hard and brittle; its crystal symmetry is [[tetragonal]] (space group ''P42/mnm'', ''a'' = 1.0194&nbsp;nm, ''c'' = 0.5313&nbsp;nm), Knoop hardness is 1000–1300 HN and electrical resistivity is relatively high at 170–210 μΩ⋅cm. The beta phase is metastable and converts to the alpha phase upon heating to 750–775&nbsp;°C. Bulk tantalum is almost entirely alpha phase, and the beta phase usually exists as thin films<ref>{{cite journal|title=Electronic structure of β-Ta films from X-ray photoelectron spectroscopy and first-principles calculations|date=2019|last1=Magnuson|first1=M.|journal=Applied Surface Science|volume=470|pages=607–612|last2=Greczynski|first2=G.|last3=Eriksson|first3=F.|last4=Hultman|first4=L.|last5=Hogberg|first5=H.|doi=10.1016/j.apsusc.2018.11.096|url=http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-152876|bibcode=2019ApSS..470..607M|s2cid=54079998}}</ref> obtained by magnetron
[[sputtering]], [[chemical vapor deposition]] or [[Electrochemistry|electrochemical deposition]] from a [[Eutectic system|eutectic]] molten salt solution.<ref>{{cite journal|doi=10.1016/j.surfcoat.2003.06.008|title=Texture, structure and phase transformation in sputter beta tantalum coating|date=2004|last1=Lee|first1=S.|journal=Surface and Coatings Technology|volume=177–178|page=44|last2=Doxbeck|first2=M.|last3=Mueller|first3=J.|last4=Cipollo|first4=M.|last5=Cote|first5=P.|url=https://zenodo.org/record/1259369}}</ref>

===Isotopes===
{{Main|Isotopes of tantalum}}

Natural tantalum consists of two stable [[isotope]]s: <sup>180m</sup>Ta (0.012%) and <sup>181</sup>Ta (99.988%). <sup>180m</sup>Ta (''m'' denotes a metastable state) is predicted to decay in three ways: [[isomeric transition]] to the [[ground state]] of <sup>180</sup>Ta, [[beta decay]] to <sup>180</sup>[[Tungsten|W]], or electron capture to <sup>180</sup>[[Hafnium|Hf]]. However, radioactivity of this [[nuclear isomer]] has never been observed, and only a lower limit on its [[half-life]] of 2.9{{e|17}}&nbsp;years has been set.<ref>{{cite journal | author= Majorana Collaboration | title=Constraints on the Decay of <sup>180m</sup>Ta | journal=Physical Review Letters | volume=131 | issue=15 | date=2023-10-11 | page=152501 | issn=0031-9007 | doi=10.1103/PhysRevLett.131.152501| pmid=37897780 | arxiv=2306.01965 }}</ref> The ground state of <sup>180</sup>Ta has a half-life of only 8 hours. <sup>180m</sup>Ta is the only naturally occurring [[nuclear isomer]] (excluding [[radiogenic]] and [[cosmogenic]] short-lived nuclides). It is also the rarest primordial isotope in the Universe, taking into account the elemental abundance of tantalum and isotopic abundance of <sup>180m</sup>Ta in the natural mixture of isotopes (and again excluding radiogenic and cosmogenic short-lived nuclides).<ref name="NUBASE">{{NUBASE 2003}}</ref>

Tantalum has been examined theoretically as a "[[Salted bomb|salting]]" material for [[nuclear weapon]]s ([[cobalt]] is the better-known hypothetical salting material). An external shell of <sup>181</sup>Ta would be irradiated by the intensive high-energy neutron flux from a hypothetical exploding nuclear weapon. This would transmute the tantalum into the radioactive isotope <sup>182</sup>Ta, which has a [[half-life]] of 114.4 days and produces [[gamma ray]]s with approximately 1.12 million electron-volts (MeV) of energy apiece, which would significantly increase the radioactivity of the [[nuclear fallout]] from the explosion for several months. Such "salted" weapons have never been built or tested, as far as is publicly known, and certainly never used as weapons.<ref>{{cite journal|last1=Win|first1=David Tin|last2=Al Masum|first2=Mohammed|title=Weapons of Mass Destruction|date=2003|journal=Assumption University Journal of Technology|volume=6|issue=4|pages=199–219|url=http://www.journal.au.edu/au_techno/2003/apr2003/aujt6-4_article07.pdf}}</ref>

Tantalum can be used as a target material for accelerated proton beams for the production of various short-lived isotopes including <sup>8</sup>Li, <sup>80</sup>Rb, and <sup>160</sup>Yb.<ref>{{cite web |title=Tantalum Target Yields – ISAC Yield Database – TRIUMF: Canada's National Laboratory for Particle and Nuclear Physics |url=https://mis.triumf.ca/science/planning/yield/target/Ta |website=mis.triumf.ca}}</ref>