[DOC] [TLE] actinium (Ac) | chemical element | Britannica.com [PAR] Ac radioactive chemical element, in Group 3 (IIIb) of the periodic table, atomic 
number 89. ... The most common isotope of actinium is actinium-227; the others, 
natural and ... has a 21.8-year half-life and in turn decays almost entirely to 
thorium-227, ... resembling the rare-earth lanthanoid elements in its chemical 
properties. [DOC] [TLE] Actinium Textual Description [POP] - ISOTOPE INFO [PAR] Traces of the longest lived radioactive isotope, actinium-227, are produced from 
... products after 185 days, thereafter decaying according to its 21.8 year halflife. [DOC] [TLE] actinium (Ac) - The Worlds of David Darling [PAR] Actinium is a silvery-white, radioactive, metallic element and first member of the 
actinide ... Its most stable isotope, 227Ac, with a half-life of 21.8 years, is a decay
... [DOC] [TLE] Actinium | Article about actinium by The Free Dictionary [PAR] Find out information about actinium. radioactive chemical element; symbol Ac; at. 
no. ... The pure metal can be prepared by reducing its fluoride with lithium vapor 
at ... The longest-lived actinium isotope, 227Ac (half-life T=21.8 years), emits... [DOC] [TLE] actinium series facts, information, pictures | Encyclopedia.com ... [PAR] Neither the element nor its compounds have any important uses. ... A radioactive 
isotope is one that breaks apart and gives off some form of radiation. The half 
lives of actinium-227 and actinium-228 are 21.77 years and 6.13 hours, ... The 
longest-lived isotope has a mass number of 227 and a half-life of 21.8 years. 
Actinium... [DOC] [TLE] Francium - Wikipedia [PAR] Francium is a chemical element with symbol Fr and atomic number 87. It used to 
be known as eka-caesium and actinium K. It is the second-least electronegative 
element, behind only caesium. Francium is a highly radioactive metal that decays 
into astatine, radium, and ... All isotopes of francium decay into astatine, radium, 
or radon. [DOC] [TLE] Chemical Element - "orphan" Elements - Atomic, Weight, Symbol ... [PAR] All isotopes of this element are radioactive; the half-life of its most stable isotope, 
actinium-227, is 21.8 years. Its name is from the Greek aktinos, meaning ray. [DOC] [TLE] Element, chemical - Science in Context - Gale [PAR] All isotopes of this element are radioactive; the half-life of its most stable isotope, 
actinium-227, is 21.8 years. Its name is from the Greek aktinos, meaning ray. [DOC] [TLE] Active actinium : Nature Chemistry : Nature Research [PAR] 4 days ago ... After some discussion, Debierne's actinium (for the Greek aktinos, meaning ray) 
... had the same impact as its freshly discovered radioactive neighbour, Ra. ... 
occurring isotopes of actinium are 227Ac (t1/2 = 21.8 years), which... [DOC] [TLE] Radium-223 - Wikipedia [PAR] Radium-223 (Ra-223, 223Ra) is an isotope of radium with an 11.4-day half-life, 
in contrast to the more common isotope radium-226, discovered by the Curies, 
which has a 1601-year ... Actinium-227 (half-life 21.8 years) in turn decays via 
thorium-227 (half-life 18.7 days) to radium-223. This decay path makes it 
convenient to... [DOC] [TLE] Actinide - Wikipedia [PAR] The actinide /ktnad/ or actinoid /ktnd/ (IUPAC nomenclature) 
series encompasses the 15 metallic chemical elements with atomic numbers 
from 89 to 103, actinium through lawrencium. The actinide series derives its 
name from the first element in the series, actinium. ... The radioactive decay of 
uranium produces transient amounts of actinium... [DOC] [TLE] ACTINIUM (AC/89) & THE ACTINIDE RARE EARTHS - Vectors [PAR] Jun 1, 2016 ... There are dozens of known isotopes of actinium, all radioactive. The most stable 
is Ac<227/89>, with a half-life of 21.8 years. ... years, meaning it's hardly 
radioactive at all, and the second most common isotope -- U<235/92>,... [DOC] [TLE] Actinium - Chemistry Encyclopedia - structure, uses, elements, metal ... [PAR] Actinium has thirty-six isotopes ,

Question: For the radioactive isotope Actinium-227, it's 21.8 years
Answer: Half-life