Editing Radium (section)

==Occurrence==
All isotopes of radium have half-lives much shorter than the [[age of the Earth]], so that any primordial radium would have decayed long ago. Radium nevertheless still occurs [[Radium and radon in the environment|in the environment]], as the isotopes {{sup|223}}Ra, {{sup|224}}Ra, {{sup|226}}Ra, and {{sup|228}}Ra are part of the decay chains of natural thorium and uranium isotopes; since thorium and uranium have very long half-lives,{{NUBASE2020|ref}} these [[decay product|daughters]] are continually being regenerated by their decay.{{sfn|Kirby|Salutsky|1964|page=3}} Of these four isotopes, the longest-lived is {{sup|226}}Ra (half-life 1600&nbsp;years), a decay product of natural uranium. Because of its relative longevity, {{sup|226}}Ra is the most common isotope of the element, making up about one [[parts per trillion|part per trillion]] of the Earth's crust; essentially all natural radium is {{sup|226}}Ra.{{sfn|Greenwood|Earnshaw|1997|pages=109-110}} Thus, radium is found in tiny quantities in the uranium ore [[uraninite]] and various other uranium [[minerals]], and in even tinier quantities in thorium minerals. One [[ton]] of [[uraninite|pitchblende]] typically yields about one seventh of a [[gram]] of radium.<ref>[http://periodic.lanl.gov/88.shtml "Radium"] {{Webarchive|url=https://web.archive.org/web/20121115182006/http://periodic.lanl.gov/88.shtml |date=15 November 2012 }}, Los Alamos National Laboratory. Retrieved 5 August 2009.</ref> One kilogram of the [[Earth's crust]] contains about 900&nbsp;[[picogram]]s of radium, and one [[liter]] of [[sea water]] contains about 89&nbsp;[[femtogram]]s of radium.<ref name="Raabundance">Section 14, Geophysics, Astronomy, and Acoustics; Abundance of Elements in the Earth's Crust and in the Sea, in Lide, David R. (ed.), ''[[CRC Handbook of Chemistry and Physics]], 85th Edition''. CRC Press. Boca Raton, Florida (2005).</ref>