# Actinium ## 🧊 Actinium · 3D (three.js) <iframe src="https://wikitube-elements.netlify.app/?el=Ac&embed=1" width="100%" height="620" frameborder="0" style="border:0;border-radius:12px;overflow:hidden" allowfullscreen loading="lazy" title="The Elements 3D microsim - Actinium"></iframe> *Actinium in the live three.js Elements explorer — drag to orbit the atom, click any tile to compare, slide the temperature.* · [▶ open full](https://wikitube-elements.netlify.app/?el=Ac) <!-- ELEMENTS_MICROSIM:END --> !Actinium plate.svg *Plate 89 of 118 - animated Bohr shells, stylized per Madelung filling; engraving style per house Arcanity kit.* ## Microsim To Do *Claimable rows, house pattern. Real Wikipedia articles only.* - Actinide - the f-block series and actinium as its first member - Uranium-235 decay chain - actinium-235 as the series parent - Nuclear medicine - actinium isotopes in targeted alpha therapy - [[Half-life|Half-life]] - actinium-227 at 21.77 years and radiometric dating ## Links (Wikipedia order) <!-- injected from _registry/childlinks/Actinium.json (2026-07-30T02:09:12Z) --> `Acetaldehyde` · `Acetate` · `Actin` · `Actinide` · `Actinide_concept` · `Actinium(III)_bromide` · `Actinium(III)_chloride` · `Actinium(III)_fluoride` · `Actinium(III)_hydroxide` · `Actinium(III)_iodide` · `Actinium(III)_nitrate` · `Actinium(III)_oxide` · `Actinium(III)_oxybromide` · `Actinium(III)_phosphate` · `Actinium(III)_sulfide` · `Actinium-225` · `Actinium_compounds` · `Actinium_oxychloride` · `Actinium_oxyfluoride` · `Actium` · `Alkali_metal` · `Alkaline_earth_metal` · [[Alpha_decay]] · [[Alpha_particle]] · [[Aluminium]] · `Aluminium_bromide` · [[Americium]] · `Ammonia` · 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Infobox grounded in [Wikipedia: List of chemical elements](https://en.wikipedia.org/wiki/List_of_chemical_elements), fetched 2026-07-08. Full article: [Wikipedia: Actinium](https://en.wikipedia.org/wiki/Actinium). <!-- ELEMENTS_MICROSIM:BEGIN (auto-managed block - edits inside will be overwritten) --> ## Key facts (infobox) | | | |---|---| | Symbol - Z | Ac - 89 | | Group - Period - Block | f - 7 - f-block | | Atomic weight (Da) | [227] | | Density (g/cm3) | 10 | | Melting - Boiling (K) | 1323 - 3471 | | Electronegativity (Pauling) | 1.1 | | Crustal abundance (mg/kg) | 5.5e-10 | | Origin | from decay | | Phase (STP) | solid | | Name origin | Greek aktis, 'ray' | *Bracketed weights are the mass number of the most stable isotope; values in parentheses are predictions (per the source table).* ## Story Actinium was discovered in 1899 by André-Louis Debierne in the residue left after extracting radium from pitchblende ore. It is rare and radioactive, with the most stable isotope, actinium-227, having a half-life of 21.77 years. Actinium is the first member of the actinides, the f-block series of elements whose chemistry is dominated by the filling of the 5f electron orbitals. The element's name comes from the Greek *aktis*, meaning "ray," reflecting its radioactivity. Actinium is a silvery white metal that is intensely radioactive and highly toxic. It is found primarily as a decay product of uranium-235 (the head of the actinium-235 decay series). Because of its extreme rarity and the difficulty of isolating it in useful quantities, actinium has no significant industrial applications. [model-prior - verify] Some actinium compounds have been studied for medical applications, particularly in targeted radiotherapy where the isotope's decay products can damage cancer cells. In this corpus, actinium stands at the head of the f-block and marks the beginning of the actinide series—a region where the chemistry becomes increasingly dominated by nuclear considerations rather than simple chemical properties. It is a gateway to the transuranium realm. ## Corpus connections Actinium marks the start of the f-block actinides and heads the uranium-235 decay chain. It links the early radioactive elements to the transuranium region. - R.E.A.C.T.I.O.N. - the Chemistry hub - Centers of Excellence Portal - [[Technetium|Technetium - the element made before found]] - the canon's patron - and Technitium, the School - [Actinide](https://en.wikipedia.org/wiki/Actinide) - the f-block series where actinium is the first member - [Uranium-235 decay chain](https://en.wikipedia.org/wiki/Decay_chain) - actinium-235 is the head of this series ## Vocational-Technical Semiotics The element speaks the canon's shared signs: the periodic table cell (Ac, group f, period 7), isotope notation, and hazard pictograms ghs where handling demands it. ## Sources Infobox: [en.wikipedia.org/wiki/List_of_chemical_elements](https://en.wikipedia.org/wiki/List_of_chemical_elements) (fetched 2026-07-08); etymology per the same table's notes. Story sources to be added at enrichment. ## Navigation - Canon: Elements Canon index - neighbors by Z: [[Radium|Radium (88)]] - [[Thorium|Thorium (90)]] - R.E.A.C.T.I.O.N. - Centers of Excellence ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Actinium) : [Wikitube](https://en.wikitube.io/wiki/Actinium) ## Previous hub tags Tree parents: [[Helium]] · [[Hydrogen]] · [[Oxygen]]. Legacy hubs: none. --- *Sources: 1 legacy note. Minted wave 1, 2026-07-30 (v1.6 order).*