Editing Radium (section)

==Isotopes==
{{main|Isotopes of radium}}
[[File:Decay chain(4n+2, Uranium series).svg|thumb|upright=1.25|left|[[Decay chain]] of {{sup|238}}U, the primordial [[progenitor]] of {{sup|226}}Ra]]
Radium has 33&nbsp;known isotopes with [[mass number]]s from 202 to 234, all of which are [[radioactive]].{{NUBASE2020|ref}} Four of these – [[radium-223|{{sup|223}}Ra]] ([[half-life]] 11.4&nbsp;days), {{sup|224}}Ra (3.64&nbsp;days), {{sup|226}}Ra (1600&nbsp;years), and {{sup|228}}Ra (5.75&nbsp;years) – occur naturally in the [[decay chain]]s of primordial [[thorium-232]], [[uranium-235]], and [[uranium-238]] ({{sup|223}}Ra from uranium-235, {{sup|226}}Ra from uranium-238, and the other two from thorium-232). These isotopes nevertheless still have [[half-lives]] too short to be [[primordial nuclide|primordial radionuclides]], and only exist in nature from these decay chains.{{sfn|Kirby|Salutsky|1964|page=3}}
Together with the mostly [[synthetic radioisotope|artificial]] {{sup|225}}Ra (15&nbsp;d), which occurs in nature only as a decay product of minute traces of [[neptunium-237]],<ref name="4n1">
{{cite journal
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 |last3=Gray    |first3=P.R.     |last4=Mech  |first4=J.F
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 |title=Occurrence of the (4{{mvar|n}} + 1) series in nature
 |journal=[[Journal of the American Chemical Society]]
 |volume=74 |issue=23 |pages=6081–6084
 |doi=10.1021/ja01143a074
 |bibcode=1952JAChS..74.6081P |url=https://digital.library.unt.edu/ark:/67531/metadc172698/
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 |archive-date=28 July 2019
}}
</ref>
these are the five most stable isotopes of radium.{{NUBASE2020|ref}} All other 27&nbsp;known radium isotopes have half-lives under two hours, and the majority have half-lives under a minute.{{NUBASE2020|ref}} Of these, {{sup|221}}Ra (half-life 28&nbsp;s) also occurs as a {{sup|237}}Np daughter, and {{sup|220}}Ra and {{sup|222}}Ra would be produced by the still-unobserved [[double beta decay]] of natural [[Isotopes of radon | radon isotopes]].<ref name="Tretyak2002">{{Cite journal
 |last1=Tretyak |first1=V.I. 
 |last2=Zdesenko |first2=Yu.G. 
 |year=2002
 |title=Tables of Double Beta Decay Data — An Update
 |journal=[[At. Data Nucl. Data Tables]] |volume=80 |issue=1 |pages=83–116
 |doi=10.1006/adnd.2001.0873
|bibcode=2002ADNDT..80...83T }}</ref> At least 12&nbsp;[[nuclear isomer]]s have been reported, the most stable of which is radium-205m with a half-life between 130~230&nbsp;milliseconds; this is still shorter than twenty-four [[ground state|ground-state]] radium isotopes.{{NUBASE2020|ref}}

{{sup|226}}Ra is the most stable isotope of radium and is the last isotope in the {{nobr|(4{{mvar|n}} + 2)}} decay chain of uranium-238 with a half-life of over a millennium; it makes up almost all of natural radium. Its immediate decay product is the dense radioactive [[noble gas]] [[radon]] (specifically the isotope [[radon-222|{{sup|222}}Rn]]), which is responsible for much of the danger of environmental radium.<ref name=epa/>{{efn | See [[radon mitigation]].}} It is 2.7&nbsp;million times more radioactive than the same [[amount of substance|molar amount]] of natural [[uranium]] (mostly uranium-238), due to its proportionally shorter half-life.<ref>
{{cite book
 | last = Soddy  | first = Frederick
 | date = 25 August 2004
 | title = The Interpretation of Radium
 | isbn = 978-0-486-43877-1
 | page = 139&nbsp;ff
 | publisher = Courier Corporation
 | url = https://books.google.com/books?id=ojaelt2o7AQC&pg=PA139
 | access-date = 27 June 2015  | url-status = live  | via = Google Books
 | archive-url = https://web.archive.org/web/20150905172755/https://books.google.com/books?id=ojaelt2o7AQC&pg=PA139
 | archive-date = 5 September 2015
}}
</ref><ref>
{{cite book
 | last1 = Malley | first1 = Marjorie C.
 | year = 2011
 | title = Radioactivity
 | publisher = Oxford University Press
 | isbn = 978-0-19-983178-4
 | url = https://archive.org/details/radioactivityhis0000mall
 | url-access = registration  | access-date = 27 June 2015  | via = Internet Archive (archive.org)
 | page = [https://archive.org/details/radioactivityhis0000mall/page/115 115&nbsp;ff]
}}</ref>

A sample of radium metal maintains itself at a higher [[temperature]] than its surroundings because of the radiation it emits. Natural radium (which is mostly {{sup|226}}Ra) emits mostly [[alpha particles]], but other steps in its decay chain (the [[Decay chain#Uranium series|uranium or radium series]]) emit alpha or [[beta particles]], and almost all particle emissions are accompanied by [[gamma rays]].<ref>{{cite book | url = https://books.google.com/books?id=alC0vvE-ZUwC&pg=PA133 | page = 133 | title = The Becquerel Rays and the Properties of Radium | isbn = 978-0-486-43875-7 | last1 = Strutt | first1 = R.J. | date = 7 September 2004 | publisher = Courier Corporation | access-date = 27 June 2015 | archive-url = https://web.archive.org/web/20150905174214/https://books.google.com/books?id=alC0vvE-ZUwC&pg=PA133 | archive-date = 5 September 2015 | url-status = live }}</ref>

Experimental nuclear physics studies have shown that nuclei of several radium isotopes, such as  {{sup|222}}Ra, {{sup|224}}Ra and {{sup|226}}Ra, have reflection-asymmetric ("pear-like") shapes.<ref>{{cite journal|title=Pear-shaped atomic nuclei|last1 = Butler| first1 = P. A.|journal = Proceedings of the Royal Society A|date=2020 | volume = 476| issue = 2239|page=20200202|doi=10.1098/rspa.2020.0202 |pmid=32821242 |bibcode=2020RSPSA.47600202B |pmc=7426035}}.</ref> In particular, this experimental information on radium-224
has been obtained at [[ISOLDE]] using a technique called [[Coulomb excitation]].<ref>{{cite web|url=https://home.cern/about/updates/2013/05/first-observations-short-lived-pear-shaped-atomic-nuclei|title=First observations of short-lived pear-shaped atomic nuclei – CERN|website=home.cern|access-date=8 June 2018|archive-url=https://web.archive.org/web/20180612145136/https://home.cern/about/updates/2013/05/first-observations-short-lived-pear-shaped-atomic-nuclei|archive-date=12 June 2018|url-status=live}}</ref><ref name=":0">{{cite journal| title = Studies of pear-shaped nuclei using accelerated radioactive beams| year = 2013| last1 = Gaffney| first1 = L. P.| last2 = Butler| first2 = P. A.| last3 = Scheck| first3 = M.| display-authors = etal | journal = Nature| volume = 497| issue = 7448| pages = 199–204| doi = 10.1038/nature12073| pmid = 23657348| bibcode = 2013Natur.497..199G| s2cid = 4380776| url = https://lirias.kuleuven.be/handle/123456789/400663}}</ref>