Atomic Weight of Thorium | Commission on Isotopic Abundances and Atomic Weights

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head> <title>Atomic Weight of Thorium | Commission on Isotopic Abundances and Atomic Weights</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <link rel="stylesheet" type="text/css" media="all" href="stylesheet.css"><link rel="shortcut icon" href="favicon.ico" /> <link href="css/theme.blue.css" rel="stylesheet" type="text/css"/> <script type="text/javascript" src="js/jquery-1.11.1.min.js"></script> <script type="text/javascript" src="js/jquery.tablesorter.js"></script> <script type="text/javascript" src="js/jquery.tablesorter.min.js"></script> <script type="text/javascript" src="js/jquery.tablesorter.widgets.js"></script> <script language="JavaScript" type="text/javascript"> $(function() { $("#mytable").tablesorter({theme:'blue',headers:{3:{sorter:'brace'},4:{sorter:false}},widgets:['zebra'],widthFixed:true}); }); </script> <script type="text/javascript"> var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-37565923-4']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); </script> </head> <body> <div id="pagewidth"> <div id="header-top" class="clearfix">  <div id="support-navigation"> <ul></ul> </div>   <div id="logo-top"> <a href="http://www.ciaaw.org"><img src="images/ciaaw.png" alt="Logo of the Atomic Weights Commission"></a> <a href="http://www.iupac.org" target="_blank"><img src="images/iupac.png" class="xx" alt="Logo of the International Union of Pure and Applied Chemistry"></a> </div>   <div id="main-navigation"> <ul> <li><a href="index.htm">Home</a></li> <li><a href="atomic-weights.htm">Atomic Weights</a></li> <li><a href="isotopic-abundances.htm">Isotopic Abundances</a></li> <li><a href="reference-materials.htm">Reference Materials</a></li> <li><a href="commission.htm">The Commission</a></li> <li><a href="info.htm">FAQ's</a></li> </ul> </div>  </div id="header-top">  <div id="breadcrumb"> <ul> <li><a href="index.htm">Other elements</a></li> </ul></div> <div id="content"> <div id="main-content"> <h1>Thorium</h1><p><table id="mytable" class="tablesorter"><thead><tr><th>Isotope</th><th>Atomic mass (Da)</th><th>Isotopic abundance (amount fraction)</th></tr></thead> <tbody> <tr><td><sup>230</sup>Th </td><td>230.033 132(8) </td><td>0.0002(2)</td></tr> <tr><td><sup>232</sup>Th </td><td>232.038 05(1) </td><td>0.9998(2)</td></tr> </tbody></table><br> <p> Thorium has been considered a monoisotopic element in the past. However, owing to significant abundance of its minor isotope <sup>232</sup>Th in deep-seawater, in 2013, the Commission recognized thorium as an element with two naturally-occurring isotopes and recommended <i>A</i><sub>r</sub>(Th) = 232.0377(4). </p><p> <sup>232</sup>Th is an α-emitter with a half-life of 1.40(1)×10<sup>10</sup> a, decaying through a branched series to <sup>208</sup>Pb without very long-lived intermediate isotopes. <sup>230</sup>Th is a nuclide in the <sup>238</sup>U decay series. It has a half-life of 7.54(2)×10<sup>4</sup> a, and is formed by α-decay of <sup>234</sup>U. </p><p> By virtue of its long half-life, about 80 % of the <sup>232</sup>Th present when the Earth was formed survives to this time. <sup>230</sup>Th is not generally found in substantial amounts in normal sources of thorium, but it is readily detected in deep-seawater. The <sup>232</sup>Th-<sup>208</sup>Pb decay scheme is of value to geochronology. </p> <h9><font color=red>SOURCE (TEXT)</font><br> <a href="publications.htm#P3">Atomic weights of the elements: Review 2000</a> by John R de Laeter et al. <i>Pure Appl. Chem.</i> 2003 (75) 683-800<br> <a href="publications.htm#P1">Atomic Weights of the Elements 2013</a> by Juris Meija et al. <i>Pure Appl. Chem.</i> 2016 (88) 265-291<br></h9> </h9> </div>  <div id="support-content"> <img src="images/p-table/Th.png"><p class="credit">CIAAW</p> <p class="caption"><strong>Thorium</strong><br> <i>A</i><sub>r</sub>(Th) = 232.0377(4) since 2013<br><br> The name derives from Thor, the Scandinavian god of thunder. It was discovered in the mineral thorite (ThSiO<sub>4</sub>) by the Swedish chemist Jöns Jacob Berzelius in 1828. Thorium was first isolated by the chemists D. Lely, Jr. and L. Hamburger in 1914. </p> </div id="support-content">  </div id="content">  <div id="push"></div></div id="pagewidth">  <div id="footer"> <img src="images/logo.png"><br><br> <a href="privacy.htm">Privacy policy</a>  |  <a href="impressum.htm">Impressum</a>  |  <a href="members.htm">Contact</a>  |  © CIAAW, 2007-2015 <br> </div>  </body></html>

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Atomic Weight of Thorium | Commission on Isotopic Abundances and Atomic Weights